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  Subjects -> PHYSICS (Total: 797 journals)
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PHYSICS (580 journals)            First | 1 2 3 | Last

Showing 201 - 400 of 741 Journals sorted alphabetically
International Journal of Mechanical Sciences     Hybrid Journal   (Followers: 11)
International Journal of Mechanics and Materials in Design     Hybrid Journal   (Followers: 5)
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology     Open Access   (Followers: 5)
International Journal of Micro-Nano Scale Transport     Full-text available via subscription   (Followers: 2)
International Journal of Microstructure and Materials Properties     Hybrid Journal   (Followers: 8)
International Journal of Microwave Science and Technology     Open Access   (Followers: 4)
International Journal of Modeling, Simulation, and Scientific Computing     Hybrid Journal   (Followers: 1)
International Journal of Modern Physics A     Hybrid Journal   (Followers: 16)
International Journal of Modern Physics B     Hybrid Journal   (Followers: 13)
International Journal of Modern Physics C     Hybrid Journal   (Followers: 15)
International Journal of Modern Physics D     Hybrid Journal   (Followers: 13)
International Journal of Modern Physics E     Hybrid Journal   (Followers: 16)
International Journal of Nanomanufacturing     Hybrid Journal  
International Journal of Nanoscience     Hybrid Journal   (Followers: 2)
International Journal of Nanotechnology     Hybrid Journal   (Followers: 5)
International Journal of Non-Linear Mechanics     Hybrid Journal   (Followers: 6)
International Journal of Physical Sciences     Open Access  
International Journal of Physics     Open Access   (Followers: 12)
International Journal of PIXE     Hybrid Journal   (Followers: 1)
International Journal of Plasticity     Hybrid Journal   (Followers: 6)
International Journal of Quantum Information     Hybrid Journal   (Followers: 2)
International Journal of Self-Propagating High-Temperature Synthesis     Hybrid Journal   (Followers: 2)
International Journal of Solids and Structures     Hybrid Journal   (Followers: 14)
International Journal of Surface Science and Engineering     Hybrid Journal   (Followers: 7)
International Journal of Theoretical and Applied Multiscale Mechanics     Hybrid Journal   (Followers: 2)
International Journal of Theoretical and Mathematical Physics     Open Access   (Followers: 13)
International Journal of Theoretical Physics     Hybrid Journal   (Followers: 17)
International Journal of Thermal Sciences     Hybrid Journal   (Followers: 13)
International Letters of Chemistry, Physics and Astronomy     Open Access   (Followers: 8)
International Materials Reviews     Hybrid Journal   (Followers: 12)
Inverse Problems     Hybrid Journal   (Followers: 2)
IOP Conference Series: Materials Science and Engineering     Open Access   (Followers: 6)
Iranian Journal of Medical Physics     Open Access  
Ironmaking & Steelmaking     Hybrid Journal   (Followers: 5)
Izvestiya Atmospheric and Oceanic Physics     Hybrid Journal   (Followers: 3)
Izvestiya, Physics of the Solid Earth     Hybrid Journal   (Followers: 2)
Japanese Journal of Applied Physics     Full-text available via subscription   (Followers: 3)
JCP : BioChemical Physics     Hybrid Journal   (Followers: 1)
JETP Letters     Hybrid Journal   (Followers: 4)
Journal of Adhesion Science and Technology     Hybrid Journal   (Followers: 7)
Journal of Advanced Physics     Full-text available via subscription   (Followers: 16)
Journal of Applied Mathematics and Mechanics     Full-text available via subscription   (Followers: 5)
Journal of Applied Mathematics and Physics     Open Access   (Followers: 8)
Journal of Applied Mechanics and Technical Physics     Hybrid Journal   (Followers: 5)
Journal of Applied Physics     Hybrid Journal   (Followers: 76)
Journal of Applied Remote Sensing     Hybrid Journal   (Followers: 50)
Journal of Applied Spectroscopy     Hybrid Journal   (Followers: 9)
Journal of Astrophysics     Open Access   (Followers: 40)
Journal of Astrophysics and Astronomy     Open Access   (Followers: 57)
Journal of Basic and Applied Physics     Open Access   (Followers: 3)
Journal of Building Physics     Hybrid Journal   (Followers: 1)
Journal of Chromatographic Science     Hybrid Journal   (Followers: 19)
Journal of Complex Networks     Hybrid Journal   (Followers: 1)
Journal of Composite Materials     Hybrid Journal   (Followers: 242)
Journal of Computational Physics     Hybrid Journal   (Followers: 65)
Journal of Contemporary Physics (Armenian Academy of Sciences)     Hybrid Journal   (Followers: 12)
Journal of Dynamic Systems, Measurement, and Control     Full-text available via subscription   (Followers: 13)
Journal of Elasticity     Hybrid Journal   (Followers: 5)
Journal of Electrical Bioimpedance     Full-text available via subscription   (Followers: 2)
Journal of Electron Spectroscopy and Related Phenomena     Hybrid Journal   (Followers: 3)
Journal of Electronic Materials     Hybrid Journal   (Followers: 3)
Journal of Electronics Cooling and Thermal Control     Open Access   (Followers: 4)
Journal of Engineering Materials and Technology     Full-text available via subscription   (Followers: 15)
Journal of Engineering Physics and Thermophysics     Hybrid Journal   (Followers: 1)
Journal of Experimental and Theoretical Physics     Hybrid Journal   (Followers: 4)
Journal of Fire Sciences     Hybrid Journal   (Followers: 4)
Journal of Geometry and Physics     Full-text available via subscription  
Journal of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 111)
Journal of Gravity     Open Access   (Followers: 2)
Journal of High Energy Astrophysics     Full-text available via subscription   (Followers: 38)
Journal of High Energy Physics     Hybrid Journal   (Followers: 19)
Journal of Hydrogels     Full-text available via subscription  
Journal of Hyperspectral Remote Sensing     Open Access   (Followers: 16)
Journal of Imaging     Open Access   (Followers: 2)
Journal of Information Display     Hybrid Journal  
Journal of Intelligent Material Systems and Structures     Hybrid Journal   (Followers: 3)
Journal of Lightwave Technology     Hybrid Journal   (Followers: 8)
Journal of Low Frequency Noise, Vibration and Active Control     Full-text available via subscription   (Followers: 6)
Journal of Luminescence     Hybrid Journal   (Followers: 3)
Journal of Materials Engineering and Performance     Hybrid Journal   (Followers: 24)
Journal of Materials Physics and Chemistry     Open Access   (Followers: 1)
Journal of Materials Science     Hybrid Journal   (Followers: 19)
Journal of Materials Science : Materials in Electronics     Hybrid Journal   (Followers: 3)
Journal of Materials Science : Materials in Medicine     Hybrid Journal   (Followers: 5)
Journal of Mathematical Fluid Mechanics     Hybrid Journal   (Followers: 5)
Journal of Mathematical Physics     Hybrid Journal   (Followers: 15)
Journal of Medical Imaging and Health Informatics     Full-text available via subscription  
Journal of Medical Ultrasonics     Hybrid Journal   (Followers: 2)
Journal of Micro/Nanolithography MEMS and MOEMS     Hybrid Journal   (Followers: 10)
Journal of Modern Physics     Open Access   (Followers: 8)
Journal of Molecular Spectroscopy     Hybrid Journal   (Followers: 8)
Journal of Motor Behavior     Hybrid Journal   (Followers: 10)
Journal of Multiscale Modeling     Hybrid Journal  
Journal of Nanophotonics     Hybrid Journal   (Followers: 4)
Journal of Nepal Physical Society     Open Access  
Journal of Nondestructive Evaluation     Hybrid Journal   (Followers: 9)
Journal of Nonlinear Dynamics     Open Access   (Followers: 1)
Journal of Nonlinear Mathematical Physics     Hybrid Journal   (Followers: 1)
Journal of Nuclear Physics, Material Sciences, Radiation and Applications     Open Access   (Followers: 1)
Journal of Optics     Hybrid Journal   (Followers: 8)
Journal of Physical and Chemical Reference Data     Hybrid Journal   (Followers: 4)
Journal of Physical Chemistry B     Full-text available via subscription   (Followers: 36)
Journal of Physical Chemistry C     Full-text available via subscription   (Followers: 27)
Journal of Physical Oceanography     Full-text available via subscription   (Followers: 10)
Journal of Physical Organic Chemistry     Hybrid Journal   (Followers: 7)
Journal of Physics A : Mathematical and Theoretical     Hybrid Journal   (Followers: 21)
Journal of Physics and Chemistry of Solids     Hybrid Journal   (Followers: 5)
Journal of Physics D : Applied Physics     Hybrid Journal   (Followers: 11)
Journal of Physics: Condensed Matter     Hybrid Journal   (Followers: 6)
Journal of Physics: Conference Series     Open Access   (Followers: 2)
Journal of Polymer Science Part B: Polymer Physics     Hybrid Journal   (Followers: 23)
Journal of Porous Materials     Hybrid Journal   (Followers: 3)
Journal of Porphyrins and Phthalocyanines     Hybrid Journal   (Followers: 1)
Journal of Quantitative Spectroscopy and Radiative Transfer     Hybrid Journal   (Followers: 1)
Journal of Reinforced Plastics and Composites     Hybrid Journal   (Followers: 30)
Journal of Research in Physics     Open Access   (Followers: 15)
Journal of Rheology     Full-text available via subscription   (Followers: 4)
Journal of Sandwich Structures and Materials     Hybrid Journal   (Followers: 3)
Journal of Scientific Research     Open Access  
Journal of Semiconductors     Full-text available via subscription   (Followers: 2)
Journal of Sensors     Open Access   (Followers: 18)
Journal of Sol-Gel Science and Technology     Hybrid Journal  
Journal of Solid State Lighting     Open Access  
Journal of Spectroscopy     Open Access   (Followers: 7)
Journal of Superconductivity and Novel Magnetism     Partially Free  
Journal of Synchrotron Radiation     Hybrid Journal   (Followers: 4)
Journal of Testing and Evaluation     Full-text available via subscription   (Followers: 19)
Journal of the American Society for Mass Spectrometry     Hybrid Journal   (Followers: 24)
Journal of the Brazilian Society of Mechanical Sciences     Open Access   (Followers: 2)
Journal of the ICRU     Hybrid Journal  
Journal of the Korean Physical Society     Partially Free  
Journal of Theoretical and Applied Physics     Open Access   (Followers: 8)
Journal of Tissue Engineering     Open Access   (Followers: 6)
Journal of Ultrasound in Medicine     Full-text available via subscription   (Followers: 10)
Journal of Vibration and Control     Hybrid Journal   (Followers: 38)
Journal of Visualization     Hybrid Journal   (Followers: 2)
Journal of Zhejiang University SCIENCE A     Hybrid Journal  
Jurnal Fisika     Open Access  
Jurnal NEUTRINO     Open Access  
Jurnal Pendidikan Fisika     Open Access   (Followers: 1)
Jurnal Pendidikan Fisika Indonesia (Indonesian Journal of Physics Education)     Open Access   (Followers: 1)
Jurnal Penelitian Sains (JPS)     Open Access  
Karbala International Journal of Modern Science     Open Access   (Followers: 3)
Lasers in Surgery and Medicine     Hybrid Journal   (Followers: 1)
Latvian Journal of Physics and Technical Sciences     Open Access  
Learning Technologies, IEEE Transactions on     Hybrid Journal   (Followers: 14)
Les Houches Summer School Proceedings     Full-text available via subscription   (Followers: 1)
Letters in Mathematical Physics     Hybrid Journal   (Followers: 4)
Light : Science & Applications     Open Access  
Living Reviews in Relativity     Open Access  
Living Reviews in Solar Physics     Open Access   (Followers: 1)
Lubrication Science     Hybrid Journal   (Followers: 1)
Macalester Journal of Physics and Astronomy     Open Access   (Followers: 3)
Machining Science and Technology: An International Journal     Hybrid Journal   (Followers: 3)
Magnetic Resonance Materials in Physics, Biology and Medicine     Hybrid Journal   (Followers: 2)
Magnetics Letters, IEEE     Hybrid Journal   (Followers: 6)
MAPAN     Hybrid Journal  
Mass Spectrometry Reviews     Hybrid Journal   (Followers: 29)
Matéria (Rio de Janeiro)     Open Access   (Followers: 1)
Materials & Design     Hybrid Journal   (Followers: 39)
Materials at High Temperatures     Full-text available via subscription   (Followers: 5)
Materials Chemistry and Physics     Full-text available via subscription   (Followers: 14)
Materials Research     Open Access   (Followers: 8)
Materials Research Bulletin     Hybrid Journal   (Followers: 22)
Materials Research Innovations     Hybrid Journal   (Followers: 1)
Materials Science     Hybrid Journal   (Followers: 8)
Materials Science and Engineering: A     Hybrid Journal   (Followers: 41)
Materials Science and Engineering: B     Hybrid Journal   (Followers: 19)
Materials Science and Engineering: C     Hybrid Journal   (Followers: 19)
Materials Science and Engineering: R: Reports     Hybrid Journal   (Followers: 16)
Materials Science and Technology     Hybrid Journal   (Followers: 41)
Matériaux & Techniques     Full-text available via subscription   (Followers: 2)
Mathematical Physics, Analysis and Geometry     Hybrid Journal   (Followers: 1)
Mathematics and Mechanics of Solids     Hybrid Journal   (Followers: 2)
Matter and Radiation at Extremes     Open Access  
Meccanica     Hybrid Journal  
Mechanics of Advanced Materials and Structures     Hybrid Journal   (Followers: 4)
Mechanics of Materials     Hybrid Journal   (Followers: 19)
Mechanics of Time-Dependent Materials     Hybrid Journal   (Followers: 1)
Mechanics Research Communications     Hybrid Journal   (Followers: 2)
Metamaterials     Hybrid Journal   (Followers: 2)
Micro and Nano Systems Letters     Open Access   (Followers: 5)
Microfluidics and Nanofluidics     Hybrid Journal   (Followers: 10)
Microporous and Mesoporous Materials     Hybrid Journal   (Followers: 6)
Modern Instrumentation     Open Access   (Followers: 27)
Modern Physics Letters A     Hybrid Journal   (Followers: 15)
Modern Physics Letters B     Hybrid Journal   (Followers: 11)
Molecular Astrophysics     Full-text available via subscription  
Molecular Diversity     Hybrid Journal  
Moscow University Physics Bulletin     Hybrid Journal  
Multibody System Dynamics     Hybrid Journal   (Followers: 1)
NANO     Hybrid Journal   (Followers: 6)
Nano Letters     Full-text available via subscription   (Followers: 57)
Nano Reviews & Experiments     Open Access   (Followers: 12)
Nano-Micro Letters     Open Access   (Followers: 1)
NanoBioImaging     Open Access  
Nanomechanics     Open Access  
Nanoscale and Microscale Thermophysical Engineering     Hybrid Journal   (Followers: 3)
Nanoscale Research Letters     Open Access   (Followers: 3)
Nanospectroscopy     Open Access  

  First | 1 2 3 | Last

Journal Cover Geochemistry, Geophysics, Geosystems
  [SJR: 2.439]   [H-I: 91]   [25 followers]  Follow
   Full-text available via subscription Subscription journal
   ISSN (Online) 1525-2027
   Published by AGU Homepage  [17 journals]
  • Porosity and fluid budget of a water-rich megathrust revealed with
           electromagnetic data at the Middle America Trench
    • Authors: Samer Naif; Kerry Key, Steven Constable, Rob L. Evans
      Abstract: At convergent margins, the distribution of fluids released from the downgoing slab modulates the state of stress and seismic coupling at the megathrust plate interface. However, existing geophysical data are unable to quantify the porosity along this interface. Here, we use controlled-source electromagnetic data collected across the Middle America Trench offshore Nicaragua to image the electrical conductivity structure of the outer forearc. Our results detect a highly conductive channel, inferred to be the region around the décollement, showing the entire section of water-rich seafloor sediments underthrust with the subducting lithosphere. We use an empirical model of the electrical conductivity of porous media to quantify the channel porosity. Our estimates are consistent with sediment compaction studies, showing a rapid decay of 65% to 10% porosity from the trench to 25 km landward. We constrain the channel thickness and use the porosity estimates to determine the water budget, which represents the fraction taken up by fluid. The porosity and water budget estimates show significant lateral variations that we attribute to changes in subducted sediment thickness caused by outer rise bending faults. Between 18-23 km from the trench the conductive channel broadens greatly to 1.5-2 km thick, possibly due to concentrated blind faults or sediment underplating, which suggests a sudden change in hydrogeologic structure at the plate interface. The impact of the anomalous conductor on the seismic coupling and mechanical properties of the megathrust are potentially related to the discrepancy in estimated fault slip between seismic and tsunami source inversions for the 1992 Nicaragua tsunami earthquake. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-27T03:35:33.95596-05:0
      DOI: 10.1002/2016GC006556
  • The Campi Flegrei Deep Drilling Project (CFDDP): New insight on caldera
           structure, evolution and hazard implications for the Naples area (Southern
    • Authors: Giuseppe De Natale; Claudia Troise, Darren Mark, Angela Mormone, Monica Piochi, Mauro Antonio Di Vito, Roberto Isaia, Stefano Carlino, Diana Barra, Renato Somma
      Abstract: The 501m-deep hole of the Campi Flegrei Deep Drilling Project, located west of the Naples metropolitan area and inside the Campi Flegrei caldera, gives new insight to reconstruct the volcano-tectonic evolution of this highly populated volcano. It is one of the highest risk volcanic areas in the world, but its tectonic structure, eruptive history and size of the largest eruptions are intensely debated in literature. New stratigraphic and 40Ar/39Ar geochronological dating allow us to determine, for the first time, the age of intra-caldera deposits belonging to the two highest magnitude caldera-forming eruptions (i.e. Campanian Ignimbrite, CI, 39 ka, and Neapolitan Yellow Tuff, NYT, 14.9 ka) and to estimate the amount of collapse. Tuffs from 439 m of depth yield the first 40Ar/39Ar age of c. 39 ka within the caldera, consistent with the CI. Volcanic rocks from the NYT were, moreover, detected between 250 m and 160 m. Our findings highlight: i) a reduction of the area affected by caldera collapse, which appears to not include the city of Naples; ii) a small volume of the infilling caldera deposits, particularly for the CI and iii) the need for reassessment of the collapse amounts and mechanisms related to larger eruptions. Our results also imply a revaluation of volcanic risk for the eastern caldera area, including the city of Naples. The results of this study point out that large calderas are characterized by complex collapse mechanisms and dynamics, whose understanding needs more robust constraints, which can be obtained from scientific drilling. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-27T03:30:29.546041-05:
      DOI: 10.1002/2015GC006183
  • Dating kimberlite emplacement with zircon and perovskite (U-Th)/He
    • Authors: Jessica R. Stanley; Rebecca M. Flowers
      Abstract: Kimberlites provide rich information about the composition and evolution of cratonic lithosphere. Accurate geochronology of these eruptions is key for discerning spatiotemporal trends in lithospheric evolution, but kimberlites can sometimes be difficult to date with available methods. We explored whether (U-Th)/He dating of zircon and perovskite can serve as reliable techniques for determining kimberlite emplacement ages. We obtained zircon and/or perovskite (U-Th)/He (ZHe, PHe) dates from sixteen southern African kimberlites. Most samples with abundant zircon yielded reproducible ZHe dates (≤15% dispersion) that are in good agreement with published eruption ages. The majority of dated zircon were xenocrystic. Zircons with reproducible dates were fully reset during eruption or resided at temperatures above the ZHe closure temperature prior to entrainment in the kimberlite magma. Not dating hazy and radiation damaged grains can help avoid anomalous results for more shallowly sourced zircons that underwent incomplete damage annealing and/or partial He loss during the eruptive process. All seven kimberlites dated with PHe yielded reproducible (≤15% dispersion) and reasonable results. We conducted two preliminary perovskite 4He diffusion experiments, which suggest a PHe closure temperature of >300°C. Perovskite in kimberlites is unlikely to be xenocrystic and its relatively high temperature sensitivity suggests that PHe dates will typically record emplacement rather than post-emplacement processes. ZHe and PHe geochronology can effectively date kimberlite emplacement and provide useful complements to existing techniques. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-27T03:30:22.639386-05:
      DOI: 10.1002/2016GC006519
  • High-precision U-Pb geochronology of the Jurassic Yanliao Biota from
           Jianchang (western Liaoning Province, China): Age constraints on the rise
           of feathered dinosaurs and eutherian mammals
    • Authors: Zhuyin Chu; Huaiyu He, Jahandar Ramezani, Samuel A. Bowring, Dongyu Hu, Lijun Zhang, Shaolin Zheng, Xiaolin Wang, Zhonghe Zhou, Chenglong Deng, Jinghui Guo
      Abstract: The Yanliao Biota of northeastern China comprises the oldest feathered dinosaurs, transitional pterosaurs, as well as the earliest eutherian mammals, multituberculate mammals, and new euharamiyidan species that are key elements of the Mesozoic biotic record. Recent discovery of the Yanliao Biota in the Daxishan section near the town of Linglongta, Jianchang County in western Liaoning Province have greatly enhanced our knowledge of the transition from dinosaurs to birds, primitive to derived pterosaurs, and the early evolution of mammals. Nevertheless, fundamental questions regarding the correlation of fossil-bearing strata, rates of dinosaur and mammalian evolution, and their relationship to environmental change in deep time remain unresolved due to the paucity of precise and accurate temporal constraints. These limitations underscore the importance of placing the rich fossil record of Jianchang within a high-resolution chronostratigraphic framework that has thus far been hampered by the relatively low precision of in situ radioisotopic dating techniques. Here we present high-precision U-Pb zircon geochronology by the chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) from three interstratified ash beds previously dated by secondary-ion mass spectrometry (SIMS) technique. The results constrain the key fossil horizons of the Daxishan section to an interval spanning 160.89 to 160.25 Ma with 2σ analytical uncertainties that range from ±46 to ±69 kyr. These data place the Yanliao Biota from Jianchang in the Oxfordian Stage of the Late Jurassic, and mark the Daxishan section as the site of Earth's oldest precisely dated feathered dinosaurs and eutherian mammals.
      PubDate: 2016-10-22T19:05:50.289375-05:
      DOI: 10.1002/2016GC006529
  • Precessional control on ocean productivity in the Western Pacific Warm
           Pool for the last 400 kyr: Insight from biogenic magnetite
    • Authors: Toshitsugu Yamazaki; Kazuho Horiuchi
      Abstract: The Western Pacific Warm Pool plays a significant role in large-scale atmospheric circulation and global hydrology. We conducted an environmental magnetic study of two late Pleistocene sediment cores from the western equatorial Pacific Ocean offshore of New Guinea in order to better constrain climatic and oceanographic variability, particularly spatiotemporal ocean productivity variations. Magnetic property measurements and transmission electron microscopy reveal that the magnetic mineral assemblages in the studied sediments are a mixture of biogenic and terrigenous magnetite. Variations in the acid soluble sediment component, interpreted as carbonate content, and the proportion of biogenic to terrigenous magnetite estimated from the ratio of anhysteretic to saturation remanent magnetizations are in-phase with northern hemisphere summer insolation variations. We interpret that ocean productivity increased during insolation maxima, which induced higher populations of magnetotactic bacteria through a larger nutrient supply to the seafloor. This interpretation assumes that magnetotactic bacterial populations are greatest in sediments just below the seafloor. Precessional frequencies in magnetic mineral concentration variations are suppressed after correction for carbonate dilution, whereas cyclic changes with a ∼100 kyr periodicity remain in carbonate-free magnetic concentration variations. Glacial/interglacial changes in bottom water currents may have influenced transportation and deposition of magnetic minerals. We demonstrate the usefulness of magnetic proxies for paleoceanographic studies, particularly of biogenic magnetite proxies for estimating paleoproductivity variations. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-22T10:35:27.811126-05:
      DOI: 10.1002/2016GC006446
  • Influence of continental growth on mid-ocean ridge depth
    • Authors: Shi Sim; Dave R. Stegman, Nicolas Coltice
      Abstract: The interconnectedness of life, water, and plate tectonics is strikingly apparent along mid-ocean ridges (MOR) where communities of organisms flourish off the disequilibrium of chemical potentials created by circulation of hydrothermal fluids driven by Earth's heat [Nisbet and Sleep, 2001; Staudigel et al., 2004]. Moreover, submarine hydrothermal environments may be critical for the emergence of life on Earth [Nisbet and Sleep, 2001]. Oceans were likely present in the Hadean [Valley et al., 2002; Harrison, 2009] but questions remain about early Earth's global tectonics [Van Hunen and Moyen, 2012], including when seafloor spreading began and whether mid-oceanic ridges were deep enough for maximum hydrothermal activities [Kasting et al., 2006]. For example, plate tectonics influences global sea level by driving secular variations in the volume of ocean basins due to continental growth [Flament et al., 2008]. Similarly, variations in the distribution of seafloor age and associated subsidence [Flament et al., 2008], due to assembly and dispersal of supercontinents [Coltice et al., 2012], explains the largest sea level variation over the past 140 Myr [Müller et al., 2008]. Using synthetic plate configurations derived from numerical models of mantle convection [Coltice et al., 2012, 2014] appropriate for early Earth, we show that MOR has remained submerged and its depths potentially constant over geologic time. Thus, conditions in the early Earth existed for hydrothermal vents at similar depths as today, providing environments conducive for the development of life and allowing for processes such as hydrothermal alteration of oceanic crust to influence the mantle's geochemical evolution This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-20T20:55:21.238348-05:
      DOI: 10.1002/2016GC006629
  • 3-D high-speed imaging of volcanic bomb trajectory in basaltic explosive
    • Authors: D. Gaudin; J. Taddeucci, B. F. Houghton, T. R. Orr, D. Andronico, E. Del Bello, U. Kueppers, T. Ricci, P. Scarlato
      Abstract: Imaging, in general, and high speed imaging in particular are important emerging tools for the study of explosive volcanic eruptions. However, traditional 2-D video observations cannot measure volcanic ejecta motion toward and away from the camera, strongly hindering our capability to fully determine crucial hazard-related parameters such as explosion directionality and pyroclasts' absolute velocity. In this paper, we use up to three synchronized high-speed cameras to reconstruct pyroclasts trajectories in three dimensions. Classical stereographic techniques are adapted to overcome the difficult observation conditions of active volcanic vents, including the large number of overlapping pyroclasts which may change shape in flight, variable lighting and clouding conditions, and lack of direct access to the target. In particular, we use a laser rangefinder to measure the geometry of the filming setup and manually track pyroclasts on the videos. This method reduces uncertainties to 10° in azimuth and dip angle of the pyroclasts, and down to 20% in the absolute velocity estimation. We demonstrate the potential of this approach by three examples: the development of an explosion at Stromboli, a bubble burst at Halema'uma'u lava lake, and an in-flight collision between two bombs at Stromboli.
      PubDate: 2016-10-20T02:05:27.918099-05:
      DOI: 10.1002/2016GC006560
  • Application of the probabilistic model BET_UNREST during a volcanic unrest
           simulation exercise in Dominica, Lesser Antilles
    • Authors: Robert Constantinescu; Richard Robertson, Jan M. Lindsay, Roberto Tonini, Laura Sandri, Dmitri Rouwet, Patrick Smith, Roderick Stewart
      Abstract: We report on the first ‘real-time' application of the BET_UNREST (Bayesian Event Tree for Volcanic Unrest) probabilistic model, during a VUELCO Simulation Exercise carried out on the island of Dominica, Lesser Antilles, in May 2015. Dominica has a concentration of nine potentially active volcanic centers and frequent volcanic earthquake swarms at shallow depths, intense geothermal activity and recent phreatic explosions (1997) indicate the region is still active. The exercise scenario was developed in secret by a team of scientists from University of West Indies (Trinidad and Tobago) and University of Auckland (New Zealand). The simulated unrest activity was provided to the exercise's Scientific Team in three ‘phases' through exercise injects comprising processed monitoring data. We applied the newly created BET_UNREST model through its software implementation PyBetUnrest, to estimate the probabilities of having i) unrest of ii) magmatic, hydrothermal or tectonic origin, which may or may not lead to iii) an eruption. The probabilities obtained for each simulated phase raised controversy and intense deliberations among the members of the scientific team. The results were often considered to be ‘too high', and were not included in any of the reports presented to ODM (Office for Disaster Management) revealing interesting crisis communication challenges. We concluded that the PyBetUnrest application itself was successful and brought the tool one step closer to a full implementation. However, as with any newly proposed method it needs more testing, and in order to be able to use it in the future we make a series of recommendations for future applications. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-19T10:20:25.392151-05:
      DOI: 10.1002/2016GC006485
  • 3-D density model of the upper mantle of Asia based on inversion of
           gravity and seismic tomography data
    • Authors: Mikhail K. Kaban; Ward Stolk, Magdala Tesauro, Sami El Khrepy, Nassir Al-Arifi, Fred Beekman, Sierd A.P.L. Cloetingh
      Abstract: We construct a new-generation 3D density model of the upper mantle of Asia and its surrounding areas based on a joint interpretation of several datasets. A recent model of the crust combining nearly all available seismic data is employed to calculate the impact of the crust on the gravity anomalies and observed topography and to estimate the residual mantle anomalies and residual topography. These fields are jointly inverted to calculate the density variations in the lithosphere and upper mantle down to 325 km. As an initial approximation, we estimate density variations using a seismic tomography model. Seismic velocity variations are converted into temperatures and then to density variations based on mineral physics constraints. In the Occam-type inversion, we fit both the residual mantle gravity anomalies and residual topography by finding deviations to the initial model. The obtained corrections improve the resolution of the initial model and reflect important features of the mantle structure that are not well resolved by the seismic tomography. The most significant negative corrections of the upper mantle density, found in the Siberian and East European cratons, can be associated with depleted mantle material. The most pronounced positive density anomalies are found beneath the Tarim and South Caspian basins, Barents Sea, and Bay of Bengal. We attribute these anomalies to eclogites in the uppermost mantle, which have substantially affected the evolution of the basins. Furthermore, the obtained results provide evidence for the presence of eclogites in the oceanic subducting mantle lithosphere. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-17T10:40:30.199619-05:
      DOI: 10.1002/2016GC006458
  • Present-day stress states underneath the Kumano basin to 2 km below
           seafloor based on borehole wall failures at IODP Site C0002, Nankai
           accretionary wedge
    • Authors: Chandong Chang; Insun Song
      Abstract: We constrain the state of stress to 2 km below seafloor in the Nankai accretionary prism at the Integrated Ocean Drilling Program (IODP) site C0002F, southwest Japan, based on borehole wall failures and rock strengths. The logging-while-drilling resistivity images from 872.5 to 2005.5 meters below seafloor show that drilling-mud control in riser drilling worked properly to minimize borehole wall failures. Available breakouts indicate a consistent maximum compression orientation subparallel to the subducting plate margin. Breakout analysis with drill logs suggests that breakouts occurred only when borehole pressure was slightly lowered and time lag between hole cutting and image logging was several hours. This indicates that the observed breakouts are not immediate stress-induced failure, but brought up into shape gradually with time due to other mechanisms. Laboratory investigations on deformation and failure of the cores suggest that the time-delayed breakout might be a result of progressive rock spall-out in borehole wall damage zones that occur at a stress level close to failure condition. We constrain stress magnitudes assuming that the stress state is sufficient to bring about the damage zones at the borehole wall. An integrated method utilizing breakouts, drilling-induced tensile fractures, and a leak-off test suggests that the stress states are on the boundary between strike-slip faulting and normal faulting stress regimes, and somewhat variable depending on depth. The stress magnitudes in the accretionary wedge appear to be controlled by frictional strength of the rock, such that the differential stresses are constrained by the laboratory determined frictional coefficients. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-17T10:40:26.835074-05:
      DOI: 10.1002/2016GC006562
  • Submarine groundwater discharge into typical tropical lagoons: A case
           study in Eastern Hainan Island, China
    • Authors: Xilong Wang; Jinzhou Du
      Abstract: Assessing submarine groundwater discharge (SGD) into lagoons and bays can be helpful to understand biogeochemical processes, especially nutrient dynamics. In the present paper, radium (Ra) isotopes were used to quantify SGD in two typical tropical lagoons (Laoye Lagoon (LY Lagoon) and Xiaohai Lagoon (XH Lagoon)) of Eastern Hainan Island, China. The Ra mass balance model provided evidence that SGD plays an important role in the hydrology of the LY Lagoon and the XH Lagoon, delivering average SGD fluxes of 1.7 × 106 (94 L m−2 d−1) and 1.8 × 106 (41 L m−2 d−1) m3 d−1, respectively. Tidal pumping was one of the important driving forces for SGD fluxes in the LY and the XH Lagoons. Tidal-driven SGD into the tidal channels of both lagoons can account for approximately 10% of the total SGD flux into the lagoons. In addition, the dissolved inorganic nutrient budgets were reassessed in the LY Lagoon and the XH Lagoon, which showed that SGD was the major source of nutrients entering the LY Lagoon and that the LY Lagoon behaved as a source for dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) and as a sink for dissolved silicate (DSi). Nutrient loads in the XH Lagoon were mainly derived from riverine inputs and SGD, and the XH Lagoon behaved as a source for DIP, but a sink for DIN and DSi. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-17T10:40:24.126333-05:
      DOI: 10.1002/2016GC006502
  • Asian monsoon modulation of nonsteady state diagenesis in hemipelagic
           marine sediments offshore of Japan
    • Authors: Liao Chang; Clara T. Bolton, Mark J. Dekkers, Akira Hayashida, David Heslop, Wout Krijgsman, Kazuto Kodama, Greig A. Paterson, Andrew P. Roberts, Eelco J. Rohling, Yuhji Yamamoto, Xiang Zhao
      Abstract: We have identified millennial-scale variations in magnetic mineral diagenesis from Pacific Ocean sediments offshore of Japan that we correlate with changes in organic carbon burial that were likely driven by Asian monsoon fluctuations. The correlation was determined by identifying offsets between the positions of fossil diagenetic fronts and climatically induced variations in organic carbon burial inferred from magnetic and geochemical analyses. Episodes of intense monsoon activity and attendant sediment magnetic mineral diagenesis also appear to correlate with Heinrich events, which supports the existence of climatic telecommunications between Asia and the North Atlantic region. Several lines of evidence support our conclusions: (1) fluctuations in down-core magnetic properties and diagenetic pyrite precipitation are approximately coeval; (2) localized stratigraphic intervals with relatively stronger magnetic mineral dissolution are linked to enhanced sedimentary organic carbon contents that gave rise to non-steady state diagenesis; (3) down-core variations in elemental S content provide a proxy for non-steady state diagenesis that correlate with key records of Asian monsoon variations; and (4) relict titanomagnetite that is preserved as inclusions within silicate particles, rather than secondary authigenic phases (e.g., greigite), dominates the strongly diagenetically altered sediment intervals and are protected against sulfidic dissolution. We suggest that such millennial-scale environmental modulation of non-steady state diagenesis (that creates a temporal diagenetic filter and relict magnetic mineral signatures) is likely to be common in organic-rich hemipelagic sedimentary settings with rapidly varying depositional conditions. Our work also demonstrates the usefulness of magnetic mineral inclusions for recording important environmental magnetic signals. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-17T10:35:22.606372-05:
      DOI: 10.1002/2016GC006344
  • Eruptive activity at Turrialba volcano (Costa Rica): Inferences from
           3He/4He in fumarole gases and chemistry of the products ejected during
           2014 and 2015
    • Authors: Andrea Luca Rizzo; Andrea Di Piazza, J. Maarten de Moor, Guillermo E. Alvarado, Geoffroy Avard, Maria Luisa Carapezza, Mauricio M. Mora
      Abstract: A new period of eruptive activity started at Turrialba volcano, Costa Rica, in 2010 after almost 150 years of quiescence. This activity has been characterized by sporadic explosions whose frequency clearly increased since October 2014. This study aimed to identify the mechanisms that triggered the resumption of this eruptive activity and characterize the evolution of the phenomena over the past 2 years. We integrate 3He/4He data available on fumarole gases collected in the summit area of Turrialba between 1999 and 2011 with new measurements made on samples collected between September 2014 and February 2016. The results of a petrological investigation of the products that erupted between October 2014 and May 2015 are also presented. We infer that the resumption of eruptive activity in 2010 was triggered by a replenishment of the plumbing system of Turrialba by a new batch of magma. This is supported by the increase in 3He/4He values observed since 2005 at the crater fumaroles and by comparable high values in September 2014, just before the onset of the new eruptive phase. The presence of a number of fresh and juvenile glassy shards in the erupted products increased between October 2014 and May 2015, suggesting the involvement of new magma with a composition similar to that erupted in 1864–1866. We conclude that the increase in 3He/4He at the summit fumaroles since October 2015 represents strong evidence of a new phase of magma replenishment, which implies that the level of activity remains high at the volcano. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-17T10:30:23.510383-05:
      DOI: 10.1002/2016GC006525
  • Miocene high-elevation landscape of the eastern Tibetan Plateau
    • Authors: Qiang Xu; Xiaohui Liu, Lin Ding
      Abstract: The high topography of central Asia is the most distinctive expression of the India-Asia collision, yet a broad understanding of the timing and processes involved in the development of the Tibetan Plateau remains elusive. Here, we investigate the Neogene Songpan Basin located on the eastern margin of the plateau using oxygen isotope paleoaltimetry to determine when the steep Longmen Shan margin obtained its present elevations. Hydrologically open lacustrine and fluvial-alluvial authigenic carbonates from the basin record the paleoelevations of the eastern Tibetan Plateau and suggest that the area had attained near-present elevations of ∼3000 m by the late Miocene. This reconstruction is consistent with the results from the comparison of pollen fossil to their nearest living relatives in this area (2750-3050 m). We propose that the eastern Tibetan Plateau may have attained significant elevations prior to the late Miocene through an uplift scenario involving eastward growth of the plateau between the Eocene and the Miocene. Two tectonic processes, either crustal shortening in the Oligocene-Miocene or eastward propagation of weakened lower crust starting in the Eocene, most likely thickened the crust and raised the surface of the eastern Tibetan Plateau to its present elevation by the late Miocene. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-13T03:26:07.102905-05:
      DOI: 10.1002/2016GC006437
  • Subsea ice-bearing permafrost on the U.S. Beaufort Margin: 2. Borehole
    • Authors: C. Ruppel; B. Herman, L. Brothers, P. Hart
      Abstract: Borehole logging data from legacy wells directly constrain the contemporary distribution of subsea permafrost in the sedimentary section at discrete locations on the US Beaufort Margin and complement recent regional analyses of exploration seismic data to delineate the permafrost's offshore extent. Most usable borehole data were acquired on a ∼500 km stretch of the margin and within 30 km of the contemporary coastline from north of Lake Teshekpuk to nearly the US-Canada border. Relying primarily on deep resistivity logs that should be largely unaffected by drilling fluids and hole conditions, the analysis reveals the persistence of several hundred vertical meters of ice-bonded permafrost in nearshore wells near Prudhoe Bay and Foggy Island Bay, with less permafrost detected to the east and west. Permafrost is inferred beneath many barrier islands and in some nearshore and lagoonal (back-barrier) wells. The analysis of borehole logs confirms the offshore pattern of ice-bearing subsea permafrost distribution determined based on regional seismic analyses and reveals that ice content generally diminishes with distance from the coastline. Lacking better well distribution, it is not possible to determine the absolute seaward extent of ice-bearing permafrost, nor the distribution of permafrost beneath the present-day continental shelf at the end of the Pleistocene. However, the recovery of gas hydrate from an outer shelf well (Belcher) and previous delineation of a log signature possibly indicating gas hydrate in an inner shelf well (Hammerhead 2) imply that permafrost may once have extended across much of the shelf offshore Camden Bay. (248 words) This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-11T08:36:07.168739-05:
      DOI: 10.1002/2016GC006582
  • Subsea ice-bearing permafrost on the U.S. Beaufort Margin: 1. Minimum
           seaward extent defined from multichannel seismic reflection data
    • Authors: Laura L. Brothers; Bruce M. Herman, Patrick E. Hart, Carolyn D. Ruppel
      Abstract: Subsea ice-bearing permafrost (IBPF) and associated gas hydrate in the Arctic have been subject to a warming climate and saline intrusion since the last transgression at the end of the Pleistocene. The consequent degradation of IBPF is potentially associated with significant degassing of dissociating gas hydrate deposits. Previous studies interpreted the distribution of subsea permafrost on the US Beaufort continental shelf based on geographically sparse datasets and modeling of expected thermal history. The most cited work projects subsea permafrost to the shelf edge (∼100-m isobath). This study uses a compilation of stacking velocity analyses from ∼100,000 line-km of industry-collected multichannel seismic reflection data acquired over 57,000 km2 of the US Beaufort shelf to delineate continuous subsea IBPF. Gridded average velocities of the uppermost 750 ms two-way travel time range from 1475 to 3110 m s−1. The monotonic, cross-shore pattern in velocity distribution suggests that the seaward extent of continuous IBPF is within 37 km of the modern shoreline at water depths 
      PubDate: 2016-10-11T08:30:51.0019-05:00
      DOI: 10.1002/2016GC006584
  • Magnetic and geochemical signatures of flood layers in a lake system
    • Authors: Eivind W. N. Støren; Øyvind Paasche, Ann M. Hirt, Monika Kumari
      Abstract: River floods holds the capasity to erode and transport sediments that are deposited whenever the discharge is redused. In catchments that are subjected to repeated flooding, downstream lakes can therefore contain a record of past events across multiple timescales. High-resolution core scanning analyses such as X-ray fluorescence (XRF) scanning and magnetic susceptibility (MS) provide data that are frequently used to detect flood layers in soft sediment archives such as lakes, fjords and ocean basins. Deposits of past floods also can potentially reveal information about the evolution of flood events as well as source area. Here we explore ways in which subtle variability in high-resolution data can be utilized and subsequently vetted by high-precision measurements in order to delineate the copious information that can be extracted from soft sediment records. By combining magnetic hysteresis measurements and first-order reversal curves (FORCs) with inductively coupled plasma optical emission spectrometer (ICP-OES) measurements of chemical elements on 36 samples, questions about flood dynamics and variability are raised, and also sources of noise in high-resolution scanning techniques are discussed. Specifically, we show that a lake flood record from Southern Norway containing 92 floods distributed over 10,000 years can be sub-divided into two groups of floods that were generated either by spring snow melting, intense summer rainstorms, or a combination of both. The temporal evolution of this pattern shows a marked shift towards spring floods around 2000 years ago compared to the earlier part of the record. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-11T08:30:45.466588-05:
      DOI: 10.1002/2016GC006540
  • The change in contact angle at unsaturated CO2-water conditions:
           Implication on geological carbon dioxide sequestration
    • Authors: Mohammad Jafari; Jongwon Jung
      Abstract: The performance of a geologic carbon storage site strongly depends on the capillary pressure of sealing rock and formations. While wettability of minerals is a key factor in capillary pressure, published contact angles are inconsistent. This study explores the discrepancy of published contact angles in order to reduce the uncertainty of measured laboratory contact angles, and understand the variation of contact angles at unsaturated CO2-water conditions. A ratio of droplet dimension and triple line (or contact line) are used to explain the observed wide range of contact angles and the variation of contact angle at unsaturated conditions. Results show that the shape factor has a good agreement with contact angle change during CO2 dissolution in water. Silica substrate has clear two pinned and slip stages of triple line during CO2 droplet dissolution, which cause contact angle on silica substrate to increase from 34.5º to 42.1º. However, mica substrate has the repeated pinned and slip stages due to the heterogeneity of mica surface, which cause contact angle to increase dramatically from 25.4º to 68.1º. Thus, both the impact of the unsaturated CO2-water conditions on the wide range of contact angle and the heterogeneity of mineral surface should be considered when one estimates capillary pressure based on contact angle in geological CO2 sequestration. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-04T10:21:34.43699-05:0
      DOI: 10.1002/2016GC006510
  • Tectonic structure of the mid-Atlantic Ridge near 16°30'N
    • Authors: Ross Parnell-Turner; Hans Schouten, Deborah K. Smith
      Abstract: The 16°30'N area of the Mid-Atlantic Ridge represents an area of present-day detachment faulting. Here we present shipboard bathymetric, magnetic and gravity data acquired up to 65 km from the ridge axis that reveal a varied tectonic history of this region. Magnetic data are used to calculate spreading rates and examine spreading rate variability along and across the axis. Bathymetric and gravity data are used to infer the crustal structure. A central magnetic anomaly 40% narrower than expected is observed along much of the study area. Misalignment between modern-day spreading center and magnetic anomalies indicates tectonic reorganization of the axis within the past 780 ka. Observed magnetic anomalies show a pattern of anomalous skewness consistent with rotation of magnetic vectors probably associated with detachment faulting. Relatively thin crust north of a small (∼7 km) non-transform offset coincides with a weakly magmatic spreading axis. In contrast, to the south a robust axial volcanic ridge is underlain by thicker crust. Variations in crustal structure perpendicular to the axis occur over tens of kilometers, indicating processes which occur over timescales of 1-2 Ma. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-04T10:21:33.434126-05:
      DOI: 10.1002/2016GC006514
  • Hydrothermal fluid venting in the offshore sector of Campi Flegrei
           caldera: A geochemical, geophysical, and volcanological study
    • Authors: R. Di Napoli; A. Aiuppa, A. Sulli, S. Caliro, G. Chiodini, V. Acocella, G. Ciraolo, M.A. Di Vito, F. Interbartolo, C. Nasello, M. Valenza
      Abstract: The ongoing unrest at the Campi Flegrei caldera (CFc) in southern Italy is prompting exploration of its poorly studied offshore sector. We report on a multidisciplinary investigation of the Secca delle Fumose (SdF), a submarine relief known since antiquity as the largest degassing structure of the offshore sector of CFc. We combined high-resolution morpho-bathymetric and seismo-stratigraphic data with onshore geological information to propose that the present-day SdF morphology and structure developed during the initial stages of the last CFc eruption at Monte Nuovo in AD 1538. We suggest that the SdF relief stands on the eastern uplifted border of a N-S-trending graben-like structure formed during the shallow emplacement of the Monte Nuovo feeding dike. We also infer that the high-angle bordering faults that generated the SdF relief now preferentially allow the ascent of hot brines (with an equilibrium temperature of 179°C), thereby sustaining hydrothermal degassing on the seafloor. Systematic vertical seawater profiling shows that hydrothermal seafloor venting generates a sizeable CO2, pH, and temperature anomaly in the overlying seawater column. Data for the seawater vertical profile can be used to estimate the CO2 and energy (heat) outputs from the SdF area at ∼50 tons/day (∼0.53 kg/s) and ∼80MW, respectively. In view of the cause-effect relationship with the Monte Nuovo eruption, and the substantial gas and energy outputs, we consider that the SdF hydrothermal system needs to be included in monitoring programs of the ongoing CFc unrest. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-04T10:21:31.573388-05:
      DOI: 10.1002/2016GC006494
  • Origin of ultrarear-arc magmatism at Rishiri Volcano, Kuril Arc
    • Authors: Takeshi Kuritani; Mitsuhiro Nakagawa
      Abstract: The Rishiri Volcano is located at the very rear of the Kuril Arc at its junction with the NE Japan Arc, and its 300 km depth to the slab surface is one of the deepest among the active arc volcanoes in the world. In this study, the origin of this ultra rear-arc magmatism was investigated by analyzing the basaltic lavas from the volcano. The lavas consist of low-K and high-K groups, with the low-K lavas predating the high-K lavas. Since it is unlikely that the high-K magmas are derivatives of the low-K magmas, the two magmas are thought to be derived from different source mantle materials. Analyses using multicomponent thermodynamics suggest that these magmas were both generated through the ∼2% melting of a source mantle with 0.04–0.11 wt.% H2O at 1280–1330°C and ∼2.3 GPa. The temperatures at the surface of the subducting Pacific slab, from which the slab fluids were released, were estimated to be 860–960°C for the low-K magmas and 930–1040°C for the high-K magmas. These temperatures of the slab surface are remarkably higher than those predicted by thermal models. The estimated high temperatures of the slab surface and the latest detailed seismic tomography results suggest that the low-K and high-K magmatism resulted from the progressive production of fluids at the slab surface due to heating by the injection of hot mantle materials into a relatively large-scale fracture in the distorted portion of the subducting Pacific plate. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-04T10:21:27.39338-05:0
      DOI: 10.1002/2016GC006594
  • Spawning superplumes from the midmantle: The impact of spin transitions in
           the mantle
    • Authors: M. H. Shahnas; R.N. Pysklywec, D. A. Yuen
      Abstract: The formation of large scale upwellings with lateral extents of several hundreds of kilometers, reaching up to ∼10000 km or more, still remains a hotly debated topic. Some seismic imaging studies based on high resolution data suggest that the main superplumes underneath Africa and South-central Pacific are clusters, composed of several individual plumes rather than being a single large mantle upwelling. The iron spin transition in the lower mantle minerals may present a new idea on the origin and the formation of such superplumes, notably sourcing such features in the mid-mantle. Stagnation of both cold sinking slabs and hot rising plumes can be caused by density and viscosity variation due to the spin transition in iron in ferropericlase (Fp) and a possible spin-dependent bulk modulus hardening in bridgmanite silicate perovskite (Pv). This process produces intermittent downward spin transition-induced mid-mantle avalanches (SIMMA) of the cold sinking flow as well as upward spin transition-induced mid-mantle superplume avalanches (SIMMSA) of the rising hot plumes, triggered at the spin transition-induced thermal boundary layer at around 1600 km depth. Our high resolution axi-symmetric models reveal that the hot upwellings, trapped below ∼1600 km depth, can suddenly penetrate into the upper levels in the mantle and spread laterally for hundreds of kilometres. Owing to the upward penetration of the mid-mantle rooted superplumes, as broad as ∼1500 km across, a large amount of heat can be delivered to the upper mantle and base of the lithosphere with implications for large volcanic episodes. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-04T10:21:01.575037-05:
      DOI: 10.1002/2016GC006509
  • Reconciling mantle wedge thermal structure with arc lava thermobarometric
           determinations in oceanic subduction zones
    • Authors: Alexander Perrin; Saskia Goes, Julie Prytulak, D Rhodri Davies, Cian Wilson, Stephan Kramer
      Abstract: Subduction zone mantle wedge temperatures impact plate interaction, melt generation, and chemical recycling. However, it has been challenging to reconcile geophysical and geochemical constraints on wedge thermal structure. Here we chemically determine the equilibration pressures and temperatures of primitive arc lavas from worldwide intra-oceanic subduction zones and compare them to kinematically driven thermal wedge models. We find that equilibration pressures are typically located in the lithosphere, starting just below the Moho, and spanning a wide depth range of ∼25 km. Equilibration temperatures are high for these depths, averaging ∼1300°C. We test for correlations with subduction parameters and find that equilibration pressures correlate with upper plate age, indicating overriding lithosphere thickness plays a role in magma equilibration. We suggest that most, if not all, thermobarometric pressure and temperature conditions reflect magmatic re-equilibration at a mechanical boundary, rather than reflecting the conditions of major melt generation. The magma re-equilibration conditions are difficult to reconcile, to a first order, with any of the conditions predicted by our dynamic models, with the exception of subduction zones with very young, thin upper plates. For most zones, a mechanism for substantially thinning the overriding plate is required. Most likely thinning is localised below the arc, as kinematic thinning above the wedge corner would lead to a hot forearc, incompatible with forearc surface heat flow and seismic properties. Localised sub-arc thermal erosion is consistent with seismic imaging and exhumed arc structures. Furthermore, such thermal erosion can serve as a weakness zone and affect subsequent plate evolution. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-04T10:20:55.837532-05:
      DOI: 10.1002/2016GC006527
  • Time-scales of foam stability in shallow conduits: Insights from analogue
    • Authors: L. Spina; B. Scheu, C. Cimarelli, A. Arciniega-Ceballos, D.B. Dingwell
      Abstract: Volcanic systems can exhibit periodical trends in degassing activity, characterized by a wide range of time-scales. Understanding the dynamics that control such periodic behavior can provide a picture of the processes occurring in the feeding system. Towards this end, we analyzed the periodicity of outgassing in a series of decompression experiments performed on analogue material (argon-saturated silicone oil plus glass beads/fibers) scaled to serve as models of basaltic magma. To define the effects of liquid viscosity and crystal content on the time-scale of outgassing we investigated both: 1) pure liquid systems, at differing viscosities (100 and 1000 Pa s), 2) particle-bearing suspensions (diluted and semi-diluted). The results indicate that under dynamic conditions (e.g. decompressive bubble growth, fluid ascent within the conduit), the periodicity of foam disruption may be up to several orders of magnitude less than estimates based on the analysis of static conditions. This difference in foam disruption time-scale is inferred to result from the contribution of bubble shear and bubble growth to inter-bubble film thinning. The presence of particles in the semi-diluted regime is further linked to shorter bubble bursting times, likely resulting from contributions of the presence of a solid network and coalescence processes to the relative increase in bubble break-up rates. Finally, it is argued that these experiments represent a good analogue of gas-piston activity (i.e., the periodical rise-and-fall of a basaltic lava lake surface), implying a dominant role for shallow foam accumulation as a source process for these phenomena. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-04T10:15:42.639335-05:
      DOI: 10.1002/2016GC006455
  • Sources and turnover of organic carbon and methane in fjord and shelf
           sediments off Northern Norway
    • Authors: Simone Sauer; Wei-Li Hong, Jochen Knies, Aivo Lepland, Matthias Forwick, Martin Klug, Florian Eichinger, Soma Baranwal, Antoine Crémière, Shyam Chand, Carsten J. Schubert
      Abstract: To better understand the present and past carbon cycling and transformation processes in methane influenced fjord and shelf areas of Northern Norway we compared two sediment cores from the Hola trough and from Ullsfjorden. We investigated (1) the organic matter composition and sedimentological characteristics to study the sources of organic carbon (Corg) and the factors influencing Corg burial, (2) pore water geochemistry to determine the contribution of organoclastic sulfate reduction and methanogenesis to total organic carbon turnover, and (3) the carbon isotopic signature of hydrocarbons to identify the carbon transformation processes and gas sources.High sedimentation and Corg accumulation rates in Ullsfjorden support the notion that fjords are important Corg sinks. The depth of the sulfate-methane-transition (SMT) in the fjord is controlled by the supply of predominantly marine organic matter to the sediment. Organoclastic sulfate reduction accounts for 60% of the total depth-integrated sulfate reduction in the fjord. In spite of the presence of ethane, propane and butane, we suggest a purely microbial origin of light hydrocarbons in the sediments based on their low δ13C values.In the Hola trough, sedimentation and Corg accumulation rates changed during the deglacial-to-post-glacial transition from approximately 80 cm ka−1 to erosion at present. Thus, Corg burial in this part of the shelf is presently absent. Low organic matter content in the sediment and low rates of organoclastic sulfate reduction (only 3% of total depth-integrated sulfate reduction) entail that the shallow depth of the SMT is controlled mostly by ascending thermogenic methane from deeper sources. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-04T10:11:36.496836-05:
      DOI: 10.1002/2016GC006296
  • Structure of magma reservoirs beneath Merapi and surrounding volcanic
           centers of Central Java modeled from ambient noise tomography
    • Authors: Ivan Koulakov; Gulzhamal Maksotova, Kayrly Jaxybulatov, Ekaterina Kasatkina, Nikolai M. Shapiro, Birger-G. Luehr, Sami El Khrepy, Nassir Al-Arifi
      Abstract: We present a three-dimensional model of the distribution of S-wave velocity in the upper crust to a depth of 20 km beneath Central Java based on the analysis of seismic ambient noise data recorded by more than 100 seismic stations in 2004 associated with the MERAMEX project. To invert the Rayleigh wave dispersion curves to construct 2D group-velocity maps and 3D distributions of S-wave velocity, we have used a new tomographic algorithm based on iterative linearized inversion. We have performed a series of synthetic tests that demonstrate significantly higher resolution in the upper crust with this model compared to the local earthquake travel-time tomography (LET) model previously applied for the same station network. Beneath the southern flank of Merapi, we identify a large low-velocity anomaly that can be split into two layers. The upper layer reflects the ∼ 1 km thick sedimentary cover of volcanoclastic deposits. The deeper anomaly at depths of ∼ 4–8 km may represent a magma reservoir with partially molten rock that feeds several volcanoes in Central Java. Beneath the Merapi summit, we observe another low-velocity anomaly as deep as 8 km that may be associated with the active magma reservoir that feeds the eruptive activity of Merapi. In the southern portion of the study area, in the lower crust, we identify a low-velocity anomaly that may represent the top of the pathways of volatiles and melts ascending from the slab that was previously inferred from the LET model results. We observe that this anomaly is clearly separate from the felsic magma reservoirs in the upper crust. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-04T10:11:29.017074-05:
      DOI: 10.1002/2016GC006442
  • Preglacial to glacial sediment thickness grids for the southern Pacific
           Margin of West Antarctica
    • Authors: Ansa Lindeque; Karsten Gohl, Florian Wobbe, Gabriele Uenzelmann-Neben
      Abstract: Circum-Antarctic sediment thickness grids provide constraints for basin evolution and paleotopographic reconstructions, which are important for paleo-ice sheet formation histories. By compiling old and new seismic data, we identify sequences representing pre-glacial, transitional and full glacial deposition processes along the Pacific margin of West Antarctica. The pre-glacial sediment grid depicts 1.3 to 4.0 km thick depocenters, relatively evenly distributed along the margin. The depocenters change markedly in the transitional phase at, or after, the Eocene/Oligocene boundary, when the first major ice sheets reached the shelf. Full glacial sequences, starting in the middle Miocene, indicate new depocenter formation North of the Amundsen Sea Embayment and localized eastward shifts in the Bellingshausen Sea and Antarctic Peninsula basins. Using present-day drainage paths and source areas on the continent, our calculations indicate an estimated observed total sedimentary volume of ∼10 x 106 km3 was eroded from West Antarctica since the separation of New Zealand in the Late Cretaceous. Of this 4.9 x 106 km3 predates the onset of glaciation and need to be considered for a paleotopography reconstruction of 34 Ma. Whereas 5.1 x 106 km3 postdate the onset of glaciation, of which 2.5 x 106 km3 were deposited in post mid-Miocene full glacial conditions. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-03T04:11:49.208516-05:
      DOI: 10.1002/2016GC006401
  • Effect of melt/mantle interactions on MORB chemistry at the easternmost
           Southwest Indian Ridge (61 to 67°E)
    • Authors: M. Paquet; M. Cannat, D. Brunelli, C. Hamelin, E. Humler
      Abstract: The easternmost part of the Southwest Indian Ridge (61°-67°E) is an end-member of the global ridge system in terms of very low magma supply. As such, it is a good laboratory to investigate the effect of melt/mantle interactions on the composition of erupted basalts: for a given volume of erupted basaltic melt, the volume of reacted mantle is potentially greater than at more magmatically robust ridges. We analyzed major, trace element and isotopic compositions in three groups of rocks: plagioclase-bearing ultramafic and gabbroic rocks dredged in nearly amagmatic spreading corridors; basalts from the sparse volcanic cover of these corridors (“ultramafic seafloor basalts”); and basalts dredged from the intervening, more volcanically active domains (“volcanic seafloor basalts”). Ultramafic seafloor basalts have significantly lower CaO and Al2O3 contents at a given MgO than most volcanic seafloor basalts. We propose that both types of basalts are derived from similar parental melts, but that the ultramafic seafloor basalts are more affected by reactions between these parent melts and the mantle rocks in the lithosphere below the ridge. We infer that these reactions occur in the walls of conduits that allow the aggregated melts extracted from the melting mantle to rise through the axial lithosphere and to the eruption sites. The principal effect of these reactions is to enrich the asthenospheric melts in MgO through olivine dissolution. This effect is not expected to be as noticeable, but could still play a role in basalt petrogenesis at more magmatic regions of the global slow-spreading MOR system. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-03T04:07:14.459134-05:
      DOI: 10.1002/2016GC006385
  • Exploring the potential of clumped isotope thermometry on coccolith‐rich
           sediments as a sea surface temperature proxy
    • Authors: Anna Joy Drury; Cédric M. John
      Abstract: Understanding past changes in sea surface temperatures (SSTs) is crucial; however, existing proxies for reconstructing past SSTs are hindered by unknown ancient seawater composition (foraminiferal Mg/Ca and δ18O), or reflect subsurface temperatures (TEX86) or have a limited applicable temperature range (Uk'37). We examine clumped isotope (Δ47) thermometry to fossil coccolith‐rich material as an SST proxy, as clumped isotopes are independent of original seawater composition and applicable to a wide temperature range and coccolithophores are widespread and dissolution resistant. The Δ47‐derived temperatures from
      PubDate: 2016-09-29T04:11:02.355559-05:
      DOI: 10.1002/2016GC006459
  • The Fina Nagu Volcanic Complex: Unusual submarine arc volcanism in the
           rapidly deforming southern Mariana margin
    • Authors: Maryjo N. Brounce; Katherine A. Kelley, Robert Stern, Fernando Martinez, Elizabeth Cottrell
      Abstract: In the Mariana convergent margin, large arc volcanoes disappear south of Guam even though the Pacific plate continues to subduct and instead, small cones scatter on the seafloor. These small cones could form either due to decompression melting accompanying back‐arc extension or flux melting, as expected for arc volcanoes, or as a result of both processes. Here, we report the major, trace, and volatile element compositions, as well as the oxidation state of Fe, in recently‐dredged, fresh pillow lavas from the Fina Nagu volcanic chain, an unusual alignment of small, closely‐spaced submarine calderas and cones southwest of Guam. We show that Fina Nagu magmas are the consequence of mantle melting due to infiltrating aqueous fluids and sediment melts sourced from the subducting Pacific plate into a depleted mantle wedge, similar in extent of melting to accepted models for arc melts. Fina Nagu magmas are not as oxidized as magmas elsewhere along the Mariana arc, suggesting that the subduction component responsible for producing arc magmas is either different or not present in the zone of melt generation for Fina Nagu, and that amphibole or serpentine mineral destabilization reactions are key in producing oxidized arc magmas. Individual Fina Nagu volcanic structures are smaller in volume than Mariana arc volcanoes, although the estimated cumulative volume of the volcanic chain is similar to nearby submarine arc volcanoes. We conclude that melt generation under the Fina Nagu chain occurs by similar mechanisms as under Mariana arc volcanoes, but that complex lithospheric deformation in the region distributes the melts among several small edifices that get younger to the northeast. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-29T03:47:32.643149-05:
      DOI: 10.1002/2016GC006457
  • Influence of microscale weak zones on bulk strength
    • Authors: Christopher Gerbi; Scott E. Johnson, Deborah Shulman, Keith Klepeis
      Abstract: Shear zones have different rheological properties than the surrounding rocks, indicating that the bulk strength of regions containing shear zone networks cannot be determined by considering the the host rock rheology alone. We demonstrate the value of this concept at the microscale. We first consider the phase arrangements in naturally deformed rocks and document that weak phases exhibit little interconnection within a microstructure. Rather, three‐dimensional weak zones, analogous to viscous shear zones, can interconnect or bridge weak phases. These zones typically form at high stress sites, comprise multiple minerals, and deform by mechanisms independent of those in the surrounding minerals. The presence of weak zones strongly affects the bulk strength of the rock, disproportionate to the mode of the weak zones. For example, the development of 1% mode of a weak zone at a high stress site can reduce the bulk strength of the rock nearly an order of magnitude. Calculation of the bulk strength of the rock by some averaging algorithm of the deformation mechanisms operating outside the weak zones will overestimate strength. Instead, accurate calculations and predictions of bulk strength require accounting for the presence and geometry of weak zones. For this reason, we advocate use of the scale‐independent conceptual rheological model of interconnected weak zones or layers rather than that of interconnected weak phases. More generally, the way forward in improving quantification of the mechanical properties of the lithosphere requires recognizing and explicitly accounting for the spatial and temporal distribution of deformation mechanisms operating throughout a rock. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-29T03:47:11.596491-05:
      DOI: 10.1002/2016GC006551
  • Late Cenozoic tephrostratigraphy offshore the southern Central American
           Volcanic Arc: 2. Implications for magma production rates and subduction
    • Authors: J.C. Schindlbeck; S. Kutterolf, A. Freundt, S.M. Straub, P. Vannucchi, G.E. Alvarado
      Abstract: Pacific drill sites offshore Central America provide the unique opportunity to study the evolution of large explosive volcanism and the geotectonic evolution of the continental margin back into the Neogene. The temporal distribution of tephra layers established by tephrochonostratigraphy in Part 1 indicates a nearly continuous highly explosive eruption record for the Costa Rican and the Nicaraguan volcanic arc within the last 8 M.y.The widely distributed marine tephra layers comprise the major fraction of the respective erupted tephra volumes and masses thus providing insights into regional and temporal variations of large‐magnitude explosive eruptions along the southern Central American Volcanic Arc (CAVA). We observe three pulses of enhanced explosive magmatism between 0‐1 Ma at the Cordillera Central, between 1‐2 Ma at the Guanacaste and at >3 Ma at the Western Nicaragua segments. Averaged over the long‐term the minimum erupted magma flux (per unit arc length) is ∼0.017 g/ms.Tephra ages, constrained by Ar‐Ar dating and by correlation with dated terrestrial tephras, yield time‐variable accumulation rates of the intercalated pelagic sediments with four prominent phases of peak sedimentation rates that relate to tectonic processes of subduction erosion. The peak rate at >2.3 Ma near Osa particularly relates to initial Cocos Ridge subduction which began at 2.91±0.23 Ma as inferred by the 1.5 M.y. delayed appearance of the OIB geochemical signal in tephras from Barva volcano at 1.42 Ma. Subsequent tectonic re‐arrangements probably involved crustal extension on the Guanacaste segment that favored the 2‐1 Ma period of unusually massive rhyolite production. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-27T01:32:10.005754-05:
      DOI: 10.1002/2016GC006504
  • The crustal structure of the Arizona Transition Zone and southern Colorado
           Plateau from multiobservable probabilistic inversion
    • Authors: Mehdi Tork Qashqai; Juan Carlos Afonso, Yingjie Yang
      Abstract: The Arizona Transition Zone is a narrow band that separates two of the main and most contrasting tectonic provinces in western US, namely the southern Colorado Plateau and the southern Basin and Range provinces. As such, the internal crustal structure and physical state of this transitional zone hold clues for understanding i) the amalgamation of these provinces, ii) the partitioning of deformation due to both past and present‐day stress fields and iii) the role of thermal versus compositional effects in controlling surface observables. Here we employ and expand a novel multi‐observable probabilistic inversion method [Afonso et al., 2013a,b] and jointly invert fundamental mode Rayleigh phase velocities, receiver functions, surface heat flow, geoid height and absolute elevation to obtain an internally‐consistent 3D model of the temperature, density, Vs and Vp of the Arizona Transition Zone and the southern portions of the Colorado Plateau and Basin and Range. Our results confirm a significant crustal thickening from ∼ 28 km in the SW of the Arizona Transition Zone and southern Basin and Range to ∼ 48 km beneath the southern Colorado Plateau. Inverted temperatures agree well with the location of recent volcanism and indicate that the lithosphere‐asthenosphere boundary is not deeper than ∼ 70 km in most of the region. We find that major pre‐Cambrian surface structures and/or shear zones separate crustal domains with distinct bulk properties, suggesting that the juxtaposed crustal blocks still retain, at least in part, their original characteristics. However, widespread intrusions of significant volumes of mafic magmas have affected these blocks at different depths, locally overprinting their original compositions and creating highly heterogeneous crustal sections. A dominant and large‐scale internal crustal pattern of SW dipping planes/structures is evident in our models, coinciding with the orientation of deep faults previously inferred from earthquake focal mechanisms. While we cannot categorically corroborate the presence of melt or aqueous fluids within the crust, our results are compatible with these scenarios beneath some parts of the Basin and Range, the Mogollon‐Datil and Springerville volcanic fields. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-27T01:27:08.103307-05:
      DOI: 10.1002/2016GC006463
  • High‐resolution carbon cycle and seawater temperature evolution during
           the Early Jurassic (Sinemurian–Early Pliensbachian)
    • Authors: Gregory D. Price; Sarah J. Baker, Justin VanDeVelde, Marie‐Emilie Clémence
      Abstract: The Early Jurassic was marked by a progressive recovery from the end‐Triassic mass extinction and punctuated by recurring episodes of anoxia. These changes, associated with fluctuations in carbon isotope composition of marine carbonates, remain incompletely understood. Here we present a high‐resolution carbon and oxygen isotope record for the Early Jurassic based on well‐preserved marine mollusks (belemnites) from Dorset, UK. Our new data show a number of δ13C excursions, starting with a negative excursion at the Sinemurian–Pliensbachian boundary Event followed by lesser negative excursions showing in the Polymorphous, Jamesoni and Masseanum‐Valdani Subzones. The recognition of the Sinemurian–Pliensbachian boundary Event in this study and elsewhere suggests that observed carbon‐isotope trends are likely to represent a supra regional perturbation of the carbon cycle. A prominent positive carbon isotope event is also seen within the Pliensbachian Ibex Zone. This event is also clearly evident in the data from belemnites from Spain. This carbon isotope excursion is not, however, coincident with inferred peak temperatures. The oxygen isotope and Mg/Ca data allows the determination of a number of pronounced Pliensbachian cool events. From the low point in the Brevispina Subzone, oxygen isotopes become more negative coupled with an increase in Mg/Ca values culminating in an Early Pliensbachian thermal maximum during the Davoei Zone. Taken with existing data it appears that the Pliensbachian is characterized by 2 major warmings, firstly within the Davoei Zone followed by warming beginning in the latest Pliensbachian and peaking in the Early Toarcian. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-27T01:27:03.48118-05:0
      DOI: 10.1002/2016GC006541
  • REEBOX PRO: A forward model simulating melting of thermally and
           lithologically variable upwelling mantle
    • Authors: Eric L. Brown; Charles E. Lesher
      Abstract: The compositions and volumes of basalts erupted in divergent margin environments provide a record of the thermal, chemical, and dynamical state of their mantle source regions. To relate basalt compositions and volumes to the underlying thermochemical and dynamical state of their mantle source regions, we have developed REEBOX PRO, a compiled stand‐alone application that simulates adiabatic decompression melting of passively or actively upwelling mantle containing up to five distinct lithologies. The model calculates melt compositions using thermodynamic and experimental constraints on the melting behaviors and mineral‐melt partitioning behavior of homogeneous and lithologically heterogeneous mantle sources containing anhydrous peridotite, hydrous peridotite, harzburgite, and/or silica‐saturated/–undersaturated pyroxenite. Key model outputs include the mean composition and crustal thickness for the bulk basaltic crust, calculated for passive and active upwelling scenarios. Here, we present the mathematical formulations underlying the model and benchmark it against existing hydrous melting models and models for mid‐ocean ridge basalt formation. We show that the hydrous and anhydrous peridotite melting models incorporated in REEBOX PRO capture the essential differences in basalt composition and volume demonstrated by previous models, and constrain the ambient mantle beneath the global spreading ridge system to be between 1319 and 1366°C, depending on the relative fertility and/or water content of the mid‐ocean ridge mantle source. We also show how model outputs may be manipulated outside of the modeling program to calculate non‐traditional melt mixing scenarios. These examples highlight the flexibility of REEBOX PRO for simulating melt generation within a range of geodynamical contexts. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-26T02:58:07.808111-05:
      DOI: 10.1002/2016GC006579
  • Thermochronological evidence of a low‐angle, midcrustal detachment plane
           beneath the central South Island, New Zealand
    • Authors: Emily Warren‐Smith; Simon Lamb, Diane Seward, Euan Smith, Frédéric Herman, Tim Stern
      Abstract: Oblique continental convergence and uplift in the Southern Alps, New Zealand is largely accommodated by dextral transpression on the Alpine Fault. However, towards the south of the orogen the Alpine Fault becomes increasingly strike‐slip, despite evidence for high exhumation rates in the Pacific plate. Here, we present 41 new apatite and zircon fission‐track ages to investigate the role of the southern Alpine Fault in Pacific plate exhumation since the Miocene. Through development of a new, maximum likelihood fission‐track age calculation method (to overcome extremely low (< 0.1 ppm) 238U concentrations in apatites) we estimate the width of the fully reset apatite zone (ages 
      PubDate: 2016-09-21T11:10:35.52932-05:0
      DOI: 10.1002/2016GC006402
  • Effect of melt composition on crustal carbonate assimilation: Implications
           for the transition from calcite consumption to skarnification and
           associated CO2 degassing
    • Authors: L. B. Carter; R. Dasgupta
      Abstract: Skarns are residue of relatively low‐temperature magma‐induced decarbonation in the crust largely associated with silicic plutons. Mafic magmatic intrusions are also capable of releasing excess CO2 due to carbonate assimilation. However, the effect of mafic to silicic melt evolution on the decarbonation processes, in addition to temperature controls on carbonate‐intrusive magmatic systems, particularly at continental arcs, remains unclear. In this study, experiments performed in a piston cylinder apparatus at mid‐crustal depth (0.5 GPa) at supersolidus temperatures (900 to 1200°C) document calcite interaction with andesite and dacite melts at equilibrium under closed‐system conditions at calcite saturation in a 1:1 melt‐calcite ratio by weight. With increasing silica content in the starting melt, at similar melt fractions and identical pressure, assimilation decreases drastically (≤65% andesite‐calcite to ≤18% dacite‐calcite). In conjunction, the CaO/SiO2 ratio in melts resulting from calcite assimilation in andesitic starting material is >1, but ≤0.3 in those formed from dacite‐calcite interaction. With increasing silica‐content in the starting melt skarn mineralogy, particularly wollastonite, increases in modal abundance while diopsidic clinopyroxene decreases slightly. More CO2 is released with andesite‐calcite reaction (≤2.9 × 1011 g/y) than with more skarn‐like dacite‐calcite interaction (≤8.1 × 1010 g/y, at one volcano assuming respective calcite‐free‐superliquidus conditions and a magma flux of 1012 g/y). Our experimental results thus suggest that calcite assimilation in more mafic magmas may have first degassed a significant amount of crustal carbon before the melt evolves to more silicic compositions, producing skarn. Crustal decarbonation in long‐lived magmatic systems may hence deliver significant albeit diminishing amounts of carbon to the atmosphere and contribute to long‐term climate change. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-20T18:50:21.881601-05:
      DOI: 10.1002/2016GC006444
  • Experimental constraints on the relationship between clay abundance, clay
           fabric, and frictional behavior for the Central Deforming Zone of the San
           Andreas Fault
    • Authors: Jasmaria Wojatschke; Marco M. Scuderi, Laurence N. Warr, Brett M. Carpenter, Demian Saffer, Chris Marone
      Abstract: The presence of smectite (saponite) in fault gouge from the Central Deforming Zone of the San Andreas Fault at Parkfield, CA has been linked to low mechanical strength and aseismic slip. However, the precise relationship between clay mineral structure, fabric development, fault strength, and the stability of frictional sliding is not well understood. We address these questions through the integration of laboratory friction tests and FIB‐SEM analysis of fault rock recovered from the San Andreas Fault Observatory at Depth (SAFOD) borehole. Intact fault rock was compared with experimentally sheared fault gouge and different proportions of either quartz clasts or SAFOD clasts extracted from the sample. Nano‐textural measurements show the development of localized clay particle alignment along shear folia developed within synthetic gouges; such slip planes have multiples of random distribution (MRD) values of 3.0‐4.9. The MRD values measured are higher than previous estimates (MRD 1.5) that show lower degrees of shear localization and clay alignment averaged over larger volumes. The intact fault rock exhibits less well‐developed nano‐clay fabrics than the experimentally sheared materials, and MRD values decrease with smectite content. We show that the abundance, strength, and shape of clasts all influence fabric evolution via strain localization: quartz clasts yield more strongly developed clay fabrics than serpentine‐dominated SAFOD clasts. Our results suggest that: 1) both clay abundance and the development of nano‐scale fabrics play a role in fault zone weakening and 2) aseismic creep is promoted by slip along clay shears with >20 wt% smectite content and MRD values ≥2.7. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-19T18:55:33.539017-05:
      DOI: 10.1002/2016GC006500
  • Tidally controlled gas bubble emissions: A comprehensive study using
           long‐term monitoring data from the NEPTUNE cabled observatory offshore
           Vancouver Island
    • Authors: Miriam Römer; Michael Riedel, Martin Scherwath, Martin Heesemann, George Spence
      Abstract: Long‐term monitoring over one year revealed high temporal variability of gas emissions at a cold seep in 1250 m water depth offshore Vancouver Island, British Columbia. Data from the North East Pacific Time series Underwater Networked Experiment observatory operated by Ocean Networks Canada were used. The site is equipped with a 260 kHz Imagenex sonar collecting hourly data, conductivity‐temperature‐depth sensors, bottom pressure recorders, current meter, and an ocean bottom seismograph. This enables correlation of the data and analyzing trigger mechanisms and regulating criteria of gas discharge activity. Three periods of gas emission activity were observed: (a) short activity phases of few hours lasting several months, (b) alternating activity and inactivity of up to several day‐long phases each, and (c) a period of several weeks of permanent activity. These periods can neither be explained by oceanographic conditions nor initiated by earthquakes. However, we found a clear correlation of gas emission with bottom pressure changes controlled by tides. Gas bubbles start emanating during decreasing tidal pressure. Tidally induced pressure changes also influence the subbottom fluid system by shifting the methane solubility resulting in exsolution of gas during falling tides. These pressure changes affect the equilibrium of forces allowing free gas in sediments to emanate into the water column at decreased hydrostatic load. We propose a model for the fluid system at the seep, fueled by a constant sub‐surface methane flux and a frequent tidally controlled discharge of gas bubbles into the ocean, transferable to other gas emission sites in the world's oceans. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-15T08:30:51.74655-05:0
      DOI: 10.1002/2016GC006528
  • Large‐scale tectonic cycles in Europe revealed by distinct Pb
           isotope provinces
    • Authors: Janne Blichert‐Toft; Hugo Delile, Cin‐Ty Lee, Zofia Stos‐Gale, Kjell Billström, Tom Andersen, Huhma Hannu, Francis Albarède
      Abstract: Lead isotopic systematics of U‐poor minerals, such as sulfides and feldspars, can provide unique insights into the origin and evolution of continents because these minerals ‘freeze in' the Pb isotopic composition of the crust during major tectonothermal events, allowing the history of a continent to be told through Pb isotopes. Lead model ages constrain the timing of crust formation while time‐integrated U/Pb, Th/Pb, and Th/U ratios shed light onto key geochemical processes associated with continent formation. Using ∼6800 Pb isotope measurements of primarily lead ores and minor K‐feldspar, we mapped out the Pb isotope systematics across Europe and the Mediterranean. Lead model ages define spatially distinct age provinces, consistent with major tectonic events ranging from the Paleozoic to the Proterozoic and latest Archean. However, the regions defined by time‐integrated U/Pb and Th/Pb ratios cut across the boundaries of age provinces, with high U/Pb systematics characterizing most of southern Europe. Magmatic influx, followed by segregation of dense sulfide‐rich mafic cumulates, resulted in foundering of U‐ and Th‐poor lower crust, thereby changing the bulk composition of the continental crust and leading to distinct time‐integrated U‐Th/Pb provinces. We show that the tectonic assembly of small crustal fragments leaves the crust largely undifferentiated, whereas the formation of supercontinents results in fundamental changes in the composition of the crust, identifiable in time and space by means of Pb isotope systematics. Observations based on Pb isotopes open up a new perspective on possible relationships between crustal thickness and geodynamic processes, in particular the role of crustal foundering into the mantle and the mechanisms responsible for the existence of cratons. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-15T08:25:33.51387-05:0
      DOI: 10.1002/2016GC006524
  • Unusually low 234Th in a hydrothermal effluent plume over the Southwest
           Indian Ridge
    • Authors: Weifeng Yang; Xinxing Zhang, Min Chen, Yusheng Qiu
      Abstract: Particle dynamics in hydrothermal plumes are crucial to understanding the cycling of carbon and trace elements in the global oceans, but this subject area has been poorly studied. We investigated radioactive 234Th in a hydrothermal plume of a recently discovered vent over the Southwest Indian Ridge (SWIR). Above the plume, total 234Th was in equilibrium with 238U, showing the typical characteristic of general deep water. However, there was a 234Th deficit within the plume, with 234Th/238U ratios in the 0.77‐0.91 range. Particulate 234Th accounted for ∼10% of the total 234Th, contrasting with 4% in the overlying water. On average, the scavenging and removal rates of 234Th were 17.5±2.5 dpm m−3 d−1 and 11.8±2.5 dpm m−3 d−1. The residence time of dissolved 234Th (avg. 108±8 d) was much higher than particulate 234Th (avg. 19±1 d), indicating that scavenging of 234Th from dissolved to particulate phase dominated its residence timescale. Particulate organic carbon (POC) increased 15% within the plume, compared with the overlying water. Combining the removal of 234Th and the ratio of POC to particulate 234Th, the POC removal flux was 9.3±0.6 mmol m−2 d−1. Similarly, 2.2±0.6 mmol m−2 of particulate nitrogen (PN) was removed per day from the plume. The magnitude of POC and PN removal implied an important role of the hydrothermal plume in delivering organic matter to the seafloor. This study thus reveals the different particle dynamic characteristics within the hydrothermal plume over the SWIR compared to the ordinary deep oceans. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-15T08:25:29.751443-05:
      DOI: 10.1002/2016GC006580
  • Brucite chimney formation and carbonate alteration at the Shinkai Seep
           Field, a serpentinite‐hosted vent system in the Southern Mariana Forearc
    • Authors: T. Okumura; Y. Ohara, R. J. Stern, T. Yamanaka, Y. Onishi, H. Watanabe, C. Chen, S. H. Bloomer, I. Pujana, S. Sakai, T. Ishii, K. Takai
      Abstract: Brucite‐carbonate chimneys were discovered from the deepest known (∼5700 m depth) serpentinite‐hosted ecosystem – the Shinkai Seep Field (SSF) in the southern Mariana forearc. Textural observations and geochemical analysis reveal three types (I‐III) of chimneys formed by the precipitation and dissolution of constitutive minerals. Type I chimneys are bright white to light yellow, have a spiky crystalline and wrinkled surface with microbial mat and contain more brucite; these formed as a result of rapid precipitation under high fluid discharge conditions. Type II chimneys exhibit white to dull brown coloration, tuberous textures like vascular bundles, and are covered with grayish microbial mats and dense colonies of Phyllochaetopterus. This type of chimney is characterized by inner brucite‐rich and outer carbonate rich zones and is thought to have precipitated from lower fluid discharge conditions than type I chimneys. Type III chimneys are ivory colored, have surface depressions and lack living microbial mats or animals. This type of chimney mainly consists of carbonate, and is in a dissolution stage. Stable carbon isotope compositions of carbonates in the two types (I and II) of active chimneys are extremely 13C‐enriched (up to +24.1‰), which may reflect biological 12C consumption under extremely low dissolved inorganic carbon concentration in alkaline fluid. Type III chimneys have 13C compositions indicating re‐equilibration with seawater. Our findings demonstrate for the first time that carbonate chimneys can be form below carbonate compensation depth and provide new insights about linked geologic, hydrologic, and biological processes of the global deep‐sea serpentinite‐hosted vent systems. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-10T10:21:17.262518-05:
      DOI: 10.1002/2016GC006449
  • Dependence of seismic coupling on normal fault style along the Northern
           Mid‐Atlantic Ridge
    • Authors: Jean‐Arthur Olive; Javier Escartín
      Abstract: While normal faults are essential in shaping the seafloor formed at slow‐spreading mid‐ocean ridges, information on their behavior on short (seismic cycle) time scales is limited. Here we combine catalogs of hydro‐acoustically and teleseismically recorded earthquakes to characterize the state of seismic coupling along the Northern Mid‐Atlantic Ridge (MAR) between 12 and 35ºN. Along this portion of the MAR axis, tectonic extension is either taken up by steep conjugate faults that outline well‐defined ridge‐parallel abyssal hills, or dominantly by a large‐offset detachment fault on one side of the axis.We investigate variations in seismicity and seismic moment release rates across thirty ridge sections that can be clearly characterized either as abyssal hill or detachment bearing. We find that detachment‐bearing sections are associated with significantly greater seismicity and moment release rates than abyssal hill bearing sections, but show variability that may reflect the along‐axis extent of individual detachment faults. Overall, the measured seismic moment release rates fail to account for the long‐term fault slip rates. This apparent seismic deficit could indicate a mixed‐mode of fault slip where earthquakes only account for ∼10–30% of offset build‐up at abyssal hill faults, while the rest is accommodated by some form of transient aseismic creep. We find this seismic coupling fraction to be significantly greater (∼40–60%) at individual detachment systems, which is somewhat at odds with the common inference that detachment faults can sustain long‐lived localized strain because they are weak. We therefore propose alternative interpretations for seismic coupling based on dynamic friction theory. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-10T10:05:32.020298-05:
      DOI: 10.1002/2016GC006460
  • Lithium isotopic systematics of submarine vent fluids from arc and
           back‐arc hydrothermal systems in the western Pacific
    • Authors: Daisuke Araoka; Yoshiro Nishio, Toshitaka Gamo, Kyoko Yamaoka, Hodaka Kawahata
      Abstract: The Li concentration and isotopic composition (δ7Li) in submarine vent fluids are important for oceanic Li budget and potentially useful for investigating hydrothermal systems deep under the seafloor because hydrothermal vent fluids are highly enriched in Li relative to seawater. Although Li isotopic geochemistry has been studied at mid‐ocean‐ridge (MOR) hydrothermal sites, in arc and back‐arc settings Li isotopic composition has not been systematically investigated. Here, we determined the δ7Li and 87Sr/86Sr values of 11 end‐member fluids from 5 arc and back‐arc hydrothermal systems in the western Pacific and examined Li behavior during high‐temperature water–rock interactions in different geological settings. In sediment‐starved hydrothermal systems (Manus Basin, Izu‐Bonin Arc, Mariana Trough, and North Fiji Basin), the Li concentrations (0.23–1.30 mmol/kg) and δ7Li values (+4.3‰ to +7.2‰) of the end‐member fluids are explained mainly by dissolution‐precipitation model during high‐temperature seawater–rock interactions at steady state. Low Li concentrations are attributable to temperature‐related apportioning of Li in rock into the fluid phase and phase separation process. Small variation in Li among MOR sites is probably caused by low‐temperature alteration process by diffusive hydrothermal fluids under the seafloor. In contrast, the highest Li concentrations (3.40 − 5.98 mmol/kg) and lowest δ7Li values (+1.6‰ to +2.4‰) of end‐member fluids from the Okinawa Trough demonstrate that the Li is predominantly derived from marine sediments. The variation of Li in sediment‐hosted sites can be explained by the differences in degree of hydrothermal fluid–sediment interactions associated with the thickness of the marine sediment overlying these hydrothermal sites. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-10T10:05:23.387838-05:
      DOI: 10.1002/2016GC006355
  • Ultra‐high Sensitivity Moment Magnetometry of Geological Samples
           Using Magnetic Microscopy
    • Authors: Eduardo A. Lima; Benjamin P. Weiss
      Abstract: Useful paleomagnetic information is expected to be recorded by samples with moments up to three orders of magnitude below the detection limit of standard superconducting rock magnetometers. Such samples are now detectable using recently developed magnetic microscopes, which map the magnetic fields above room‐temperature samples with unprecedented spatial resolutions and field sensitivities. However, realizing this potential requires the development of techniques for retrieving sample moments from magnetic microscopy data. With this goal, we developed a technique for uniquely obtaining the net magnetic moment of geological samples from magnetic microscopy maps of unresolved or nearly unresolved magnetization. This technique is particularly powerful for analyzing small, weakly magnetized samples such as meteoritic chondrules and terrestrial silicate crystals like zircons. We validated this technique by applying it to field maps generated from synthetic sources and also to field maps measured using a superconducting quantum interference device (SQUID) microscope above geological samples with moments down to 10−15 Am2. For the most magnetic rock samples, the net moments estimated from the SQUID microscope data are within error of independent moment measurements acquired using lower sensitivity standard rock magnetometers. In addition to its superior moment sensitivity, SQUID microscope net moment magnetometry also enables the identification and isolation of magnetic contamination and background sources, which is critical for improving accuracy in paleomagnetic studies of weakly magnetic samples. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-08T04:05:42.038885-05:
      DOI: 10.1002/2016GC006487
  • A comparison of Thellier‐type and multispecimen paleointensity
           determinations on Pleistocene and historical lava flows from Lanzarote
           (Canary Islands, Spain)
    • Authors: Manuel Calvo‐Rathert; Juan Morales‐Contreras, Ángel Carrancho, Avto Gogichaishvili
      Abstract: Sixteen Miocene, Pleistocene and historic lava flows have been sampled in Lanzarote (Canary Islands) for paleointensity analysis with both the Coe and multispecimen methods. Besides obtaining new data, the main goal of the study was the comparison of paleointensity results determined with two different techniques. Characteristic Remanent Magnetization (ChRM) directions were obtained in 15 flows and 12 were chosen for paleointensity determination. In Thellier‐type experiments a selection of reliable paleointensity determinations (43 of 78 studied samples) was performed using sets of criteria of different stringency, trying to relate the quality of results to the strictness of the chosen criteria. Uncorrected and fraction and domain‐state corrected multispecimen paleointensity results were obtained in all flows. Results with the Coe method on historical flows either agree with the expected values or show moderately lower ones, but multispecimen determinations display a large deviation from the expected result in one case. No relation can be detected between correct or anomalous results and paleointensity determination quality or rock‐magnetic properties. However, results on historical flows suggest that agreement between both methods could be a good indicator of correct determinations. Comparison of results obtained with both methods on seven Pleistocene flows yields an excellent agreement in four and disagreements in three cases. Pleistocene determinations were only accepted if either results from both methods agreed or a result was based on a sufficiently large number (n>4) of individual Thellier type determinations. In most Pleistocene flows a VADM around 5·1022Am2 was observed, although two flows displayed higher values around 9·1022Am2. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-02T10:50:29.385384-05:
      DOI: 10.1002/2016GC006396
  • The role of symbiotic algae in the formation of the coral polyp skeleton:
           3‐D morphological study based on X‐ray micro‐computed tomography
    • Authors: Shinya Iwasaki; Mayuri Inoue, Atsushi Suzuki, Osamu Sasaki, Harumasa Kano, Akira Iguchi, Kazuhiko Sakai, Hodaka Kawahata
      Abstract: Symbiotic algae of primary polyps play an important role in calcification of coral skeletons. However, the function of the symbiotic algae, including the way they influence the physical features of their host skeleton under various conditions, is not well understood. We used X‐ray micro‐computed tomography to observe skeletal shape characteristics in symbiotic and aposymbiotic primary polyps of Acropora digitifera that were cultured at various temperature and pCO2 levels (temperature 27, 29, 33 °C; pCO2 400, 800, 1000 µatm). Symbiotic polyps had a basal plate with a well‐developed folding margin supporting the branched skeleton, whereas aposymbiotic ones did not. The features of the folding margin suggest that it might be the initial growth stage of the epitheca. In addition, three‐dimensional (3‐D) morphological measurements made by X‐ray micro‐computed tomography show that the branched skeletons of symbiotic primary polyps were taller than those of aposymbiotic ones, suggesting that zooxanthellae in coral primary polyps play a critical role in the height growth of skeletal branches. Furthermore, results of the temperature‐ and pCO2‐controlled experiments suggest that global warming might greatly affect the activity of zooxanthellae, whereas ocean acidification might reduce calcification by damaging the coral host itself. Our findings provide new knowledge about the role of zooxanthellae in coral calcification. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-31T20:55:22.97819-05:0
      DOI: 10.1002/2016GC006536
  • Synchrotron X‐ray computed microtomography study on gas hydrate
           decomposition in a sedimentary matrix
    • Authors: Lei Yang; Andrzej Falenty, Marwen Chaouachi, David Haberthür, Werner F. Kuhs
      Abstract: In‐situ synchrotron X‐ray computed microtomography with sub‐micrometer voxel size was used to study the decomposition of gas hydrates in a sedimentary matrix. Xenon‐hydrate was used instead of methane hydrate to enhance the absorption contrast. The microstructural features of the decomposition process were elucidated indicating that the decomposition starts at the hydrate‐gas interface; it does not proceed at the contacts with quartz grains. Melt water accumulates at retreating hydrate surface. The decomposition is not homogeneous and the decomposition rates depend on the distance of the hydrate surface to the gas phase indicating a diffusion‐limitation of the gas transport through the water phase. Gas is found to be metastably enriched in the water phase with a concentration decreasing away from the hydrate‐water interface. The initial decomposition process facilitates redistribution of fluid phases in the pore space and local re‐formation of gas hydrates. The observations allow also rationalizing earlier conjectures from experiments with low spatial resolutions and suggest that the hydrate‐sediment assemblies remain intact until the hydrate spacers between sediment grains finally collapse; possible effects on mechanical stability and permeability are discussed. The resulting time resolved characteristics of gas hydrate decomposition and the influence of melt water on the reaction rate are of importance for a suggested gas recovery from marine sediments by depressurization. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-29T09:25:24.163631-05:
      DOI: 10.1002/2016GC006521
  • Determining the flux of methane into Hudson Canyon at the edge of methane
           clathrate hydrate stability
    • Authors: Alexander Weinstein; Luis Navarrete, Carolyn Ruppel, Thomas C. Weber, Mihai Leonte, Matthias Kellermann, Eleanor Arrington, David L. Valentine, Mary I. Scranton, John D. Kessler
      Abstract: Methane seeps were investigated in Hudson Canyon, the largest shelf‐break canyon on the northern US Atlantic Margin. The seeps investigated are located at or updip of the nominal limit of methane clathrate hydrate stability. The acoustic identification of bubble streams was used to guide water column sampling in a 32 km2 region within the canyon's thalweg. By incorporating measurements of dissolved methane concentration with methane oxidation rates and current velocity into a steady‐state box model, the total emission of methane to the water column in this region was estimated to be 12 kmol methane per day (range: 6 – 24 kmol methane per day). These analyses suggest this methane is largely retained inside the canyon walls below 300 m water depth, and that it is aerobically oxidized to near completion within the larger extent of Hudson Canyon. Based on estimated methane emissions and measured oxidation rates, the oxidation of this methane to dissolved CO2 is expected to have minimal influences on seawater pH. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-29T09:20:23.123763-05:
      DOI: 10.1002/2016GC006421
  • Mass transfer in the lower crust: Evidence for incipient melt assisted
           flow along grain boundaries in the deep arc granulites of Fiordland, New
    • Authors: Catherine A. Stuart; Sandra Piazolo, Nathan R. Daczko
      Abstract: Knowledge of mass transfer is critical in improving our understanding of crustal evolution, however mass transfer mechanisms are debated, especially in arc environments. The Pembroke Granulite is a gabbroic gneiss, passively exhumed from depths of > 45 km from the arc root of Fiordland, New Zealand. Here, enstatite and diopside grains are replaced by coronas of pargasite and quartz, which may be asymmetric, recording hydration of the gabbroic gneiss. The coronas contain microstructures indicative of the former presence of melt, supported by pseudosection modeling consistent with the reaction having occurred near the solidus of the rock (630–710°C, 8.8–12.4kbar). Homogeneous mineral chemistry in reaction products indicates an open system, despite limited metasomatism at the hand sample scale. We propose the partial replacement microstructures are a result of a reaction involving an externally‐derived hydrous, silicate melt and the relatively anhydrous, high‐grade assemblage. Trace element mapping reveals a correlation between reaction microstructure development and bands of high‐Sr plagioclase, recording pathways of the reactant melt along grain boundaries. Replacement microstructures record pathways of diffuse porous melt flow at a kilometer scale within the lower crust, which was assisted by small proportions of incipient melt providing a permeable network. This work recognizes melt flux through the lower crust in the absence of significant metasomatism, which may be more common than is currently recognized. As similar microstructures are found elsewhere within the exposed Fiordland lower crustal arc rocks, mass transfer of melt by diffuse porous flow may have fluxed an area > 10,000 km2. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-29T09:20:22.299032-05:
      DOI: 10.1002/2015GC006236
  • An experimental study of the role of subsurface plumbing on geothermal
    • Authors: Atsuko Namiki; Yoshinori Ueno, Shaul Hurwitz, Michael Manga, Carolina Munoz‐Saez, Fred Murphy
      Abstract: In order to better understand the diverse discharge styles and eruption intervals observed at geothermal features, we performed three series of laboratory experiments with differing plumbing geometries. A single, straight conduit that connects a hot water bath (flask) to a vent (funnel) can originate geyser‐like periodic eruptions, continuous discharge like a boiling spring, and fumarole‐like steam discharge, depending on the conduit length and radius. The balance between the heat loss from the conduit walls and the heat supplied from the bottom determines whether and where water can condense which in turn controls discharge style. Next, we connected the conduit to a cold water reservoir through a branch, simulating the inflow from an external water source. Colder water located at a higher place than a branching point can flow into the conduit to stop the boiling in the flask, controlling the periodicity of the eruption. When an additional branch is connected to a second cold water reservoir, the two cold reservoirs can interact. Our experiments show that branching allows new processes to occur, such as recharge of colder water and escape of steam from side channels, leading to greater variation in discharge styles and eruption intervals. This model is consistent with the fact that eruption duration is not controlled by emptying reservoirs. We show how differences in plumbing geometries can explain various discharge styles and eruption intervals observed in El Tatio, Chile and Yellowstone, USA. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-25T19:20:35.86327-05:0
      DOI: 10.1002/2016GC006472
  • Automated paleomagnetic and rock magnetic data acquisition with an
           in‐line horizontal ‘2G' system
    • Authors: Tom A.T. Mullender; Thomas Frederichs, Christian Hilgenfeldt, Lennart V. de Groot, Karl Fabian, Mark J. Dekkers
      Abstract: Today's paleomagnetic and magnetic proxy studies involve processing of large sample collections while simultaneously demanding high quality data and high reproducibility. Here we describe a fully automated interface based on a commercial horizontal pass‐through ‘2G' DC‐SQUID magnetometer. This system is operational at the universities of Bremen (Germany) and Utrecht (Netherlands) since 1998 and 2006, respectively, while a system is currently being built at NGU Trondheim (Norway). The magnetometers are equipped with ‘in‐line' alternating field (AF) demagnetization, a direct‐current bias field coil along the co‐axial AF demagnetization coil for the acquisition of anhysteretic remanent magnetization (ARM) and a long pulse‐field coil for the acquisition of isothermal remanent magnetization (IRM). Samples are contained in dedicated low magnetization perspex holders that are manipulated by a pneumatic pick‐and‐place‐unit. Upon desire samples can be measured in several positions considerably enhancing data quality in particular for magnetically weak samples. In the Bremen system, the peak of the IRM pulse fields is actively measured which reduces the discrepancy between the set field and the field that is actually applied. Techniques for quantifying and removing gyroremanent overprints and for measuring the viscosity of IRM further extend the range of applications of the system. Typically c. 300 paleomagnetic samples can be AF demagnetized per week (15 levels) in the three‐position protocol. The versatility of the system is illustrated by several examples of paleomagnetic and rock magnetic data processing. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-19T09:45:32.50452-05:0
      DOI: 10.1002/2016GC006436
  • Strain localization in polycrystalline material with second phase
           particles: Numerical modeling with application to ice mixtures
    • Authors: D. Cyprych; S. Brune, S. Piazolo, J. Quinteros
      Abstract: We use a centimeter‐scale 2D numerical model to investigate the effect of the presence of a second phase with various volume percent, shape and orientation on strain localization in a visco‐elastic matrix. In addition, the evolution of bulk rheological behavior of aggregates during uniaxial compression is analyzed. The rheological effect of dynamic recrystallization processes in the matrix is reproduced by viscous strain softening. We show that the presence of hard particles strengthens the aggregate, but also causes strain localization and the formation of ductile shear zones in the matrix. The presence of soft particles weakens the aggregate, while strain localizes within the particles and matrix between particles. The shape and the orientation of second phases controls the orientation, geometry and connectivity of ductile shear zones. We propose an analytical scaling method that translates the bulk stress measurements of our 2D simulations to 3D experiments. Comparing our model to the laboratory uniaxial compression experiments on ice cylinders with hard second phases allows the analysis of transient and steady‐state strain distribution in ice matrix, and strain partitioning between ice and second phases through empirical calibration of viscous softening parameters. We find that the ice matrix in two‐phase aggregates accommodates more strain than the applied bulk strain, while at faster strain rates some of the load is transferred into hard particles. Our study illustrates that dynamic recrystallization processes in the matrix are markedly influenced by the presence of a second phase. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-19T09:40:32.130934-05:
      DOI: 10.1002/2016GC006471
  • Radial anisotropy beneath northeast Tibet, implications for lithosphere
           deformation at a restraining bend in the Kunlun fault and its vicinity
    • Authors: Lun Li; Aibing Li, Michael A. Murphy, Yuanyuan V. Fu
      Abstract: Three‐dimensional shear wave velocity and radial anisotropy models of the crust and upper mantle beneath the NE Tibetan plateau are constructed from new measurements of Love wave dispersions (20‐77s) and previously obtained Rayleigh wave dispersions (20‐87s) using a two‐plane‐wave method. The mid‐lower crust is characterized with positive anisotropy (VSH>VSV) with large strength beneath the Qinling and Qilian Mountains and relative weak values beneath the Anyemaqen Mountain. The large positive anisotropy can be explained by horizontal alignment of anisotropic minerals in the mid‐lower crust due to crustal flow. The mantle lithosphere above 90 km is largely isotropic while weak positive anisotropy appears beneath 90 km, which probably marks the lithosphere‐asthenosphere boundary (LAB). A low shear wave velocity anomaly and relatively negative radial anisotropy are imaged in the entire lithosphere beneath the restraining bend in the eastern Kunlun fault, consistent with a weak lithosphere experiencing vertical thickening under horizontal compression. The asthenosphere at the restraining bend is characterized by significant low velocity and positive radial anisotropy, reflecting that the asthenosphere here is probably hotter, has more melts, and deforms more easily than the surrounding region. We propose that the lithosphere at the restraining bend was vertically thickened and subsequently delaminated locally, and induced asthenosphere upwelling. This model explains the observations of velocity and anisotropy anomalies in the lithosphere and asthenosphere as well as geological observations of rapid rock uplift at the restraining bend of the Kunlun fault. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-19T09:40:29.281344-05:
      DOI: 10.1002/2016GC006366
  • Shear wave anisotropy in northwestern South America and its link to the
           Caribbean and Nazca subduction geodynamics
    • Authors: J. Idárraga‐García; J. ‐M. Kendall, C. A. Vargas
      Abstract: To investigate the subduction dynamics in northwestern South America, we measured SKS and slab‐related local S splitting at 38 seismic stations. Comparison between the delay times of both phases shows that most of the SKS splitting is due to entrained mantle flow beneath the subducting Nazca and Caribbean slabs. On the other hand, the fast polarizations of local S‐waves are consistently aligned with regional faults, which implies the existence of a lithosphere‐confined anisotropy in the overriding plate, and that the mantle wedge is not contributing significantly to the splitting. Also, we identified a clear change in SKS fast directions at the trace of the Caldas Tear (∼5°N), which represents a variation in the subduction style. To the north of ∼5°N fast directions are consistently parallel to the flat subduction of the Caribbean plate‐Panama arc beneath South America, while to the south fast polarizations are subparallel to the Nazca‐South America subduction direction. A new change in the SKS splitting pattern is detected at ∼2.8ºN, which is related to another variation in the subduction geometry marked by the presence of a lithosphere‐scale tearing structure, named here as Malpelo Tear; in this region, NE‐SW‐oriented SKS fast directions are consistent with the general dip direction of the underthrusting of the Carnegie Ridge beneath South America. Further inland, this NE‐SW‐trending mantle flow continues beneath the Eastern Cordillera of Colombia and Merida Andes of Venezuela. Finally, our results suggest that the sub‐slab mantle flow in northwestern South America is strongly controlled by the presence of lithospheric tearing structures. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-19T09:40:25.436529-05:
      DOI: 10.1002/2016GC006323
  • Permeability of oceanic crustal rock samples from IODP Hole 1256D
    • Authors: L.A. Gilbert; M.L. Bona
      Abstract: Permeability is an important parameter of oceanic crust: it controls hydrothermal circulation and influences the exchange of heat and chemicals between seawater and the crust. Using the most complete section of intact, in situ normal oceanic crust, this paper presents the first permeability measurements of samples from Integrated Ocean Drilling Program (IODP) Hole 1256D in a relatively undisturbed section through lavas, dikes, and into gabbros. At in situ pressures, saturated gabbro from Hole 1256D is about half as permeable as basalt (2.4 × 10−20 m2 and 4.0 × 10−20 m2, respectively). Although fresh basalt samples have higher permeabilities, the basalts at Hole 1256D contain saponite, an alteration mineral which drastically reduces permeability. These measurements represent an opportunity for comparison to models that predict permeability at IODP Hole 1256D. Similar to model predictions, sample permeability generally decreases with depth. However, even after applying the scaling rule, models predict higher permeabilities than exhibited by the samples, suggesting large‐scale cracks still control permeability in the 15 My old crust at Hole 1256D. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-17T10:30:27.704821-05:
      DOI: 10.1002/2016GC006467
  • Horizontal compressive stress regime on the northern Cascadia margin
           inferred from borehole breakouts
    • Authors: M. Riedel; A. Malinverno, K. Wang, D. Goldberg, G. Guerin
      Abstract: During Integrated Ocean Drilling Program Expedition 311 five boreholes were drilled across the accretionary prism of the northern Cascadia subduction zone. Logging‐while‐drilling borehole images are utilized to determine breakout orientations to define maximum horizontal compressive stress orientations. Additionally, wireline logging data at two of these sites and from Site 889 of Ocean Drilling Program Leg 146 are used to define breakouts from differences in the aperture of caliper arms. At most sites, the maximum horizontal compressive stress SHmax is margin‐normal, consistent with plate convergence. Deviations from this trend reflect local structural perturbations. Our results do not constrain stress magnitudes. If the margin‐normal compressional stress is greater than the vertical stress, the margin‐normal SHmax direction we observe may reflect current locking of a velocity‐weakening shallow megathrust and thus potential for trench‐breaching, tsunamigenic rupture in a future megathrust earthquake. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-17T10:30:27.475412-05:
      DOI: 10.1002/2016GC006443
  • Large fluctuations of shallow seas in low‐lying Southeast Asia
           driven by mantle flow
    • Authors: Sabin Zahirovic; Nicolas Flament, R Dietmar Müller, Maria Seton, Michael Gurnis
      Abstract: The Sundaland continental promontory, as the core of Southeast Asia, is one of the lowest lying continental regions, with half of the continental area presently inundated by a shallow sea. The role of mantle convection in driving long‐wavelength topography and vertical motion of the lithosphere in this region has often been ignored when interpreting regional stratigraphy, including a widespread Late Cretaceous‐Eocene unconformity, despite a consensus that Southeast Asia is presently situated over a large‐amplitude, dynamic topography low resulting from long‐term post‐Pangea subduction. We use forward numerical models to link mantle flow with surface tectonics, and compare predicted trends of dynamic topography with eustasy and regional paleogeography to determine the influence of mantle convection on regional basin histories. A Late Cretaceous collision of Gondwana‐derived terranes with Sundaland choked the active margin, leading to slab breakoff and a ∼10‐15 Myr‐long subduction hiatus. Slab breakoff likely resulted in several hundred meters of dynamic uplift and emergence of Sundaland between ∼80 and 60 Ma, and may explain the absence of a Late Cretaceous‐Eocene sedimentary record. Renewed subduction from ∼60 Ma reinitiated dynamic subsidence of Sundaland, leading to submergence from ∼40 Ma despite falling long‐term global sea levels. Our results highlight a complete ‘down‐up‐down' dynamic topography cycle experienced by Sundaland, with transient dynamic topography manifesting as a major regional unconformity in sedimentary basins. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-12T10:10:26.185406-05:
      DOI: 10.1002/2016GC006434
  • Segment‐scale variations in seafloor volcanic and tectonic processes
           from multibeam sonar imaging, mid‐Atlantic Ridge Rainbow region
    • Authors: Deborah E. Eason; Robert A. Dunn, J. Pablo Canales, Robert Sohn
      Abstract: Along‐axis variations in melt supply and thermal structure can lead to significant variations in the mode of crustal accretion at mid‐ocean ridges. We examine variations in seafloor volcanic and tectonic processes on the scale of individual ridge segments in a region of the slow‐spreading Mid‐Atlantic Ridge (35º45'‐36º35'N) centered on the Rainbow non‐transform discontinuity (NTD). We use multibeam sonar backscatter amplitude data, taking advantage of multifold and multi‐directional coverage from the MARINER geophysical study to create a gridded compilation of seafloor reflectivity, and interpret the sonar image within the context of other data to examine seafloor properties and identify volcanic flow fields and tectonic features. Along the spreading segments, differences in volcanic productivity, faulting, eruption style and frequency correlate with inferred magma supply. Regions of low magma supply are associated with more widely spaced faults, and larger volcanic flow fields that are more easily identified in the backscatter image. Identified flow fields with the highest backscatter occur near the ends of ridge segments. Their relatively smooth topography contrasts with the more hummocky, cone‐dominated terrain that dominates most of the neovolcanic zone. Patches of seafloor with high, moderately high, and low backscatter intensity across the Rainbow massif are spatially correlated with observations of basalt, gabbro and serpentinized peridotite, and sediment respectively. Large detachment faults have repeatedly formed along the inside corners of the Rainbow NTD, producing a series of oceanic core complexes along the wake of the NTD. A new detachment fault is currently forming in the ridge segment just north of the now inactive Rainbow massif. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-09T04:32:15.970129-05:
      DOI: 10.1002/2016GC006433
  • Correction algorithm for on‐line continuous flow δ13C and δ18O
           carbonate and cellulose stable isotope analyses
    • Authors: M. N. Evans; K. J. Selmer, B. T. Breeden, A. S. Lopatka, R. E. Plummer
      Abstract: We describe an algorithm to correct for scale compression, runtime drift, and amplitude effects in carbonate and cellulose oxygen and carbon isotopic analyses made on two online continuous flow isotope ratio mass spectrometry (CF‐IRMS) systems using gas chromatographic (GC) separation. We validate the algorithm by correcting measurements of samples of known isotopic composition which are not used to estimate the corrections. For carbonate δ13C (δ18O) data, median precision of validation estimates for two reference materials and two calibrated working standards is 0.05% (0.07%); median bias is 0.04% (0.02%) over a range of 49.2% (24.3%). For α‐cellulose δ13C (δ18O) data, median precision of validation estimates for one reference material and five working standards is 0.11% (0.27%); median bias is 0.13% (‐0.10%) over a range of 16.1% (19.1%). These results are within the 5th‐95th percentile range of subsequent routine runtime validation exercises in which one working standard is used to calibrate the other. Analysis of the relative importance of correction steps suggests that drift and scale‐compression corrections are most reliable and valuable. If validation precisions are not already small, routine cross‐validated precision estimates are improved by up to 50% (80%). The results suggest that correction for systematic error may enable these particular CF‐IRMS systems to produce δ13C and δ18O carbonate and cellulose isotopic analyses with higher validated precision, accuracy and throughput than is typically reported for these systems. The correction scheme may be used in support of replication‐intensive research projects in paleoclimatology and other data‐intensive applications within the geosciences. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-08T05:18:17.18164-05:0
      DOI: 10.1002/2016GC006469
  • Issue Information
    • Pages: 3527 - 3528
      PubDate: 2016-10-27T02:29:29.385174-05:
      DOI: 10.1002/ggge.20836
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