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PHYSICS (576 journals)            First | 1 2 3 | Last

Showing 201 - 400 of 741 Journals sorted alphabetically
International Journal of Mechanics and Materials in Design     Hybrid Journal   (Followers: 6)
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology     Open Access   (Followers: 7)
International Journal of Microstructure and Materials Properties     Hybrid Journal   (Followers: 8)
International Journal of Microwave Science and Technology     Open Access   (Followers: 3)
International Journal of Modeling, Simulation, and Scientific Computing     Hybrid Journal   (Followers: 1)
International Journal of Modern Physics A     Hybrid Journal   (Followers: 14)
International Journal of Modern Physics B     Hybrid Journal   (Followers: 11)
International Journal of Modern Physics C     Hybrid Journal   (Followers: 14)
International Journal of Modern Physics D     Hybrid Journal   (Followers: 12)
International Journal of Modern Physics E     Hybrid Journal   (Followers: 14)
International Journal of Nanomanufacturing     Hybrid Journal  
International Journal of Nanoscience     Hybrid Journal   (Followers: 1)
International Journal of Nanotechnology     Hybrid Journal   (Followers: 7)
International Journal of Non-Linear Mechanics     Hybrid Journal   (Followers: 7)
International Journal of Nonlinear Dynamics and Control     Hybrid Journal  
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: 7)
International Journal of Quantum Information     Hybrid Journal   (Followers: 3)
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: 6)
International Journal of Theoretical and Applied Multiscale Mechanics     Hybrid Journal   (Followers: 3)
International Journal of Theoretical and Mathematical Physics     Open Access   (Followers: 12)
International Journal of Theoretical Physics     Hybrid Journal   (Followers: 18)
International Journal of Thermal Sciences     Hybrid Journal   (Followers: 16)
International Letters of Chemistry, Physics and Astronomy     Open Access   (Followers: 12)
International Materials Reviews     Hybrid Journal   (Followers: 14)
Inverse Problems     Hybrid Journal   (Followers: 3)
IOP Conference Series: Materials Science and Engineering     Open Access   (Followers: 8)
Iranian Journal of Medical Physics     Open Access  
Ironmaking & Steelmaking     Hybrid Journal   (Followers: 6)
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: 5)
JETP Letters     Hybrid Journal   (Followers: 4)
Journal of Adhesion Science and Technology     Hybrid Journal   (Followers: 10)
Journal of Advanced Physics     Full-text available via subscription   (Followers: 14)
Journal of Advances in Physics     Open Access   (Followers: 20)
Journal of Applied Mathematics and Mechanics     Full-text available via subscription   (Followers: 7)
Journal of Applied Mathematics and Physics     Open Access   (Followers: 8)
Journal of Applied Mechanics and Technical Physics     Hybrid Journal   (Followers: 7)
Journal of Applied Physics     Hybrid Journal   (Followers: 78)
Journal of Applied Remote Sensing     Hybrid Journal   (Followers: 62)
Journal of Applied Spectroscopy     Hybrid Journal   (Followers: 9)
Journal of Astrophysics and Astronomy     Open Access   (Followers: 40)
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: 16)
Journal of Complex Networks     Hybrid Journal   (Followers: 1)
Journal of Composite Materials     Hybrid Journal   (Followers: 299)
Journal of Computational Physics     Hybrid Journal   (Followers: 64)
Journal of Contemporary Physics (Armenian Academy of Sciences)     Hybrid Journal   (Followers: 11)
Journal of Dynamic Systems, Measurement, and Control     Full-text available via subscription   (Followers: 13)
Journal of Elasticity     Hybrid Journal   (Followers: 6)
Journal of Electrical Bioimpedance     Open Access   (Followers: 2)
Journal of Electron Spectroscopy and Related Phenomena     Hybrid Journal   (Followers: 3)
Journal of Electronic Materials     Hybrid Journal   (Followers: 5)
Journal of Electronics Cooling and Thermal Control     Open Access   (Followers: 5)
Journal of Engineering Materials and Technology     Full-text available via subscription   (Followers: 19)
Journal of Engineering Physics and Thermophysics     Hybrid Journal   (Followers: 1)
Journal of Experimental and Theoretical Physics     Hybrid Journal   (Followers: 3)
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: 131)
Journal of High Energy Astrophysics     Full-text available via subscription   (Followers: 24)
Journal of High Energy Physics     Hybrid Journal   (Followers: 18)
Journal of Hydrogels     Full-text available via subscription  
Journal of Hyperspectral Remote Sensing     Open Access   (Followers: 18)
Journal of Imaging     Open Access   (Followers: 3)
Journal of Information Display     Hybrid Journal   (Followers: 1)
Journal of Intelligent Material Systems and Structures     Hybrid Journal   (Followers: 6)
Journal of Lightwave Technology     Hybrid Journal   (Followers: 11)
Journal of Low Frequency Noise, Vibration and Active Control     Open Access   (Followers: 8)
Journal of Luminescence     Hybrid Journal   (Followers: 4)
Journal of Materials Engineering and Performance     Hybrid Journal   (Followers: 23)
Journal of Materials Physics and Chemistry     Open Access   (Followers: 2)
Journal of Materials Science     Hybrid Journal   (Followers: 21)
Journal of Materials Science : Materials in Electronics     Hybrid Journal   (Followers: 5)
Journal of Materials Science : Materials in Medicine     Hybrid Journal   (Followers: 5)
Journal of Mathematical Fluid Mechanics     Hybrid Journal   (Followers: 8)
Journal of Mathematical Physics     Hybrid Journal   (Followers: 25)
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: 13)
Journal of Modern Physics     Open Access   (Followers: 7)
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: 9)
Journal of Nepal Physical Society     Open Access  
Journal of Nondestructive Evaluation     Hybrid Journal   (Followers: 11)
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: 7)
Journal of Physical and Chemical Reference Data     Hybrid Journal   (Followers: 4)
Journal of Physical Chemistry B     Full-text available via subscription   (Followers: 38)
Journal of Physical Chemistry C     Full-text available via subscription   (Followers: 31)
Journal of Physical Oceanography     Full-text available via subscription   (Followers: 12)
Journal of Physical Organic Chemistry     Hybrid Journal   (Followers: 9)
Journal of Physics A : Mathematical and Theoretical     Hybrid Journal   (Followers: 20)
Journal of Physics and Chemistry of Solids     Hybrid Journal   (Followers: 5)
Journal of Physics D : Applied Physics     Hybrid Journal   (Followers: 14)
Journal of Physics: Condensed Matter     Hybrid Journal   (Followers: 6)
Journal of Physics: Conference Series     Open Access   (Followers: 2)
Journal of Plasma Physics     Hybrid Journal   (Followers: 20)
Journal of Polymer Science Part B: Polymer Physics     Hybrid Journal   (Followers: 23)
Journal of Porous Materials     Hybrid Journal   (Followers: 4)
Journal of Porphyrins and Phthalocyanines     Hybrid Journal   (Followers: 2)
Journal of Quantitative Spectroscopy and Radiative Transfer     Hybrid Journal   (Followers: 3)
Journal of Reinforced Plastics and Composites     Hybrid Journal   (Followers: 30)
Journal of Research in Physics     Open Access   (Followers: 13)
Journal of Rheology     Full-text available via subscription   (Followers: 5)
Journal of Romance Studies     Full-text available via subscription   (Followers: 2)
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: 4)
Journal of Sensors     Open Access   (Followers: 23)
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   (Followers: 1)
Journal of Synchrotron Radiation     Hybrid Journal   (Followers: 4)
Journal of Testing and Evaluation     Full-text available via subscription   (Followers: 20)
Journal of the American Society for Mass Spectrometry     Hybrid Journal   (Followers: 30)
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: 11)
Journal of Vibration and Control     Hybrid Journal   (Followers: 41)
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: 3)
Jurnal Pendidikan Fisika     Open Access  
Jurnal Pendidikan Fisika Indonesia (Indonesian Journal of Physics Education)     Open Access   (Followers: 2)
Jurnal Penelitian Fisika dan Aplikasinya     Open Access  
Jurnal Penelitian Sains (JPS)     Open Access  
Jurnal Sains dan Pendidikan Fisika     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: 2)
Lubrication Science     Hybrid Journal   (Followers: 2)
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: 3)
Magnetics Letters, IEEE     Hybrid Journal   (Followers: 7)
MAPAN     Hybrid Journal  
Mass Spectrometry Reviews     Hybrid Journal   (Followers: 31)
Matéria (Rio de Janeiro)     Open Access   (Followers: 1)
Materials & Design     Hybrid Journal   (Followers: 42)
Materials at High Temperatures     Full-text available via subscription   (Followers: 6)
Materials Chemistry and Physics     Full-text available via subscription   (Followers: 16)
Materials Research     Open Access   (Followers: 8)
Materials Research Bulletin     Hybrid Journal   (Followers: 26)
Materials Research Innovations     Hybrid Journal   (Followers: 1)
Materials Science     Hybrid Journal   (Followers: 9)
Materials Science and Engineering: A     Hybrid Journal   (Followers: 42)
Materials Science and Engineering: B     Hybrid Journal   (Followers: 20)
Materials Science and Engineering: C     Hybrid Journal   (Followers: 19)
Materials Science and Engineering: R: Reports     Hybrid Journal   (Followers: 17)
Materials Science and Technology     Hybrid Journal   (Followers: 42)
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: 3)
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: 22)
Mechanics of Time-Dependent Materials     Hybrid Journal   (Followers: 2)
Mechanics Research Communications     Hybrid Journal   (Followers: 2)
Metamaterials     Hybrid Journal   (Followers: 3)
Micro and Nano Systems Letters     Open Access   (Followers: 5)
Microfluidics and Nanofluidics     Hybrid Journal   (Followers: 10)
Microporous and Mesoporous Materials     Hybrid Journal   (Followers: 9)
Modern Instrumentation     Open Access   (Followers: 30)
Modern Physics Letters A     Hybrid Journal   (Followers: 15)
Modern Physics Letters B     Hybrid Journal   (Followers: 10)
Molecular Astrophysics     Full-text available via subscription  
Molecular Diversity     Hybrid Journal  
Moscow University Physics Bulletin     Hybrid Journal  
Multibody System Dynamics     Hybrid Journal   (Followers: 2)
NANO     Hybrid Journal   (Followers: 5)
Nano Letters     Full-text available via subscription   (Followers: 60)
Nano Reviews & Experiments     Open Access   (Followers: 13)
Nano-Micro Letters     Open Access   (Followers: 2)
NanoBioImaging     Open Access  
Nanomechanics     Open Access  
Nanoscale and Microscale Thermophysical Engineering     Hybrid Journal   (Followers: 3)
Nanoscale Research Letters     Open Access   (Followers: 5)

  First | 1 2 3 | Last

Journal Cover Geochemistry, Geophysics, Geosystems
  [SJR: 2.439]   [H-I: 91]   [30 followers]  Follow
   Full-text available via subscription Subscription journal
   ISSN (Online) 1525-2027
   Published by AGU Homepage  [17 journals]
  • MeBo70 Seabed Drilling on a Polar Continental Shelf: Operational Report
           and Lessons From Drilling in the Amundsen Sea Embayment of West Antarctica
    • Authors: K. Gohl; T. Freudenthal, C.-D. Hillenbrand, J. Klages, R. Larter, T. Bickert, S. Bohaty, W. Ehrmann, O. Esper, T. Frederichs, C. Gebhardt, K. Küssner, G. Kuhn, H. Pälike, T. Ronge, P. Simões Pereira, J. Smith, G. Uenzelmann-Neben, C. van de Flierdt,
      Abstract: A multi-barrel seabed drill rig was used for the first time to drill unconsolidated sediments and consolidated sedimentary rocks from an Antarctic shelf with core recoveries between 7 and 76%. We deployed the MARUM-MeBo70 drill device at nine drill sites in the Amundsen Sea Embayment. Three sites were located on the inner shelf of Pine Island Bay from which soft sediments, presumably deposited at high sedimentation rates in isolated small basins, were recovered from drill depths of up to 36 m below seafloor. Six sites were located on the middle shelf of the eastern and western embayment. Drilling at five of these sites recovered consolidated sediments and sedimentary rocks from dipping strata spanning ages from Late Cretaceous to Miocene. This report describes the initial coring results, the challenges posed by drifting icebergs and sea ice, and technical issues related to deployment of the MeBo70. We also present recommendations for similar future drilling campaigns on polar continental shelves.
      PubDate: 2017-10-16T01:17:07.314434-05:
      DOI: 10.1002/2017GC007081
  • Understanding Copper Isotope Behavior in the High Temperature
           Magmatic-Hydrothermal Porphyry Environment
    • Authors: Melissa J. Gregory; Ryan Mathur
      Abstract: Copper stable isotope geochemistry has the potential to constrain aspects of ore deposit formation once variations in the isotopic data can be related to the physiochemical conditions during metal deposition. This study presents Cu isotope ratios for copper sulfides from samples from the Pebble porphyry Cu-Au-Mo deposit in Alaska. The δ65Cu values range from -2.09 to 1.11 ‰ and show a series of linear correlations with the δ18O isotope ratios calculated for the fluid in equilibrium with the hydrothermal alteration in each sample. Samples with sodic-potassic, potassic and illite alteration display a negative linear correlation between the Cu and O isotope results. This suggests that fractionation of Cu isotopes between the fluid and precipitating chalcopyrite is positive as the hydrothermal fluid is evolving from magmatic to mixed magmatic-meteoric compositions. Samples with advanced argillic alteration display a weak positive linear correlation between Cu and O isotope results consistent with small negative fluid-chalcopyrite Cu isotope fractionation during fluid evolution. The hydrothermal fluids that formed sodic-potassic, potassic and illite alteration likely transported Cu as CuHS0. Hydrothermal fluids that resulted in advanced argillic alteration likely transport Cu as CuCl2-. The pH conditions also control Cu isotope fractionation, consistent with previous experimental work. Larger fractionation factors were found between fluids and chalcopyrite precipitating under neutral conditions contrasting with small fractionation factors calculated between fluids and chalcopyrite precipitating under acidic conditions. Therefore, this study proposes that hydrothermal fluid compositions and pH conditions are related to Cu isotope variations in high temperature magmatic-hydrothermal deposits.
      PubDate: 2017-10-16T01:16:33.667356-05:
      DOI: 10.1002/2017GC007026
  • Possible Icelandic Tephra Found in European Colle Gnifetti Glacier
    • Authors: M. T. Luongo; A. V. Kurbatov, T. Erhardt, P. A. Mayewski, M. McCormick, A. F. More, N. E. Spaulding, S. D. Wheatley, M. G. Yates, P. D. Bohleber
      Abstract: Volcanic ash (tephra) provides unique time markers (isochrons) that are often used as an independent age-control tool for stratigraphic correlations of paleoclimate archives from ice cores. However, little credence has been given to the notion of finding tephra in ice cores collected in the European Alps because of the relatively large distance from volcanic sources and the presumed nature of regional atmospheric circulation patterns. We filtered particles from melted ice core drilling chips gathered roughly every meter during a 2013 drilling operation at Colle Gnifetti glacier in the Swiss-Italian Alps (45°55.74′N, 7°52.58′E, 4450 m asl). One filter, preliminarily dated to the nineteenth century by annual layer counting, contained a group of six visually similar tephra particles. Analyzing their chemistry using a scanning electron microscope equipped with an energy-dispersive x-ray spectrometer established that the six particles were volcanic in origin and are very similar in composition (a distinctive geochemical signature), pointing to a single volcanic eruption source. We proposed that one of several massive nineteenth century Eastern Icelandic eruptions is a potential source given eruption timing, size, tephra dispersion area, and similarities in chemical composition. This first finding of tephra in an Alpine ice core contributes to a regional tephrochronological framework that can be adapted for future correlation among different paleoclimate sequences.
      PubDate: 2017-10-16T01:11:50.482623-05:
      DOI: 10.1002/2017GC007022
  • Registration of Precession Signal in the Last Interglacial Paleosol (S1)
           on the Chinese Loess Plateau
    • Authors: Long Ma; Ying Li, Xingxing Liu, Youbin Sun
      Abstract: Solar insolation plays an essential role in driving orbital-scale East Asian Monsoon (EAM) variability. Unlike Chinese speleothem δ18O records characterized by dominant precessional cycles, many loess proxies from the Chinese Loess Plateau (CLP) usually display damped precessional-scale variability. To reconcile the precessional monsoon variability recorded in two classic archives, it's critical to investigate which factors can significantly affect the sensitivity of loess proxies to precessional forcing. In this study, we synthesize grain size (GS) and magnetic susceptibility (χ) results of eighteen paleosol (S1) profiles over the CLP, with effort to evaluating the relative impacts of sedimentation rate (SR) and pedogenesis on the precessional signal intensity (PSI) during the last interglaciation. Based on unified grain-size age models, amplitude contrast between normalized GS and χ variations of five substages of the last interglaciation is employed to infer the PSI. The results indicate that precessional signals are evident in the GS/χ records of the high-SR loess profiles on the northern and western CLP. Comparison of the PSI variations with the SR and mean annual precipitation (MAP) changes suggests that the GS-PSI is positively correlated to the SR changes, whilst the χ-PSI is negatively/positively related to the SR/MAP changes. Our results confirm that distinct precessional cycles in high-resolution loess proxies permit a plausible reconciliation of monsoon variability recorded in Chinese loess and speleothem.
      PubDate: 2017-10-16T01:11:35.805163-05:
      DOI: 10.1002/2017GC006964
  • Reconstructing the Evolution of the Submarine Monterey Canyon System From
           Os, Nd, and Pb Isotopes in Hydrogenetic Fe-Mn Crusts
    • Authors: T. A. Conrad; S. G. Nielsen, B. Peucker-Ehrenbrink, J. Blusztajn, D. Winslow, J. R. Hein, A. Paytan
      Abstract: The sources of terrestrial material delivered to the California margin over the past 7 Myr were assessed using 187Os/188Os, Nd, and Pb isotopes in hydrogenetic ferromanganese crusts from three seamounts along the central and southern California margin. From 6.8 to 4.5 (± 0.5) Ma, all three isotope systems show more radiogenic values at Davidson Seamount, located near the base of the Monterey Canyon System, than in Fe-Mn crusts from the more remote Taney and Hoss seamounts. At the Taney seamounts, approximately 225 km farther offshore from Davidson Seamount, 187Os/188Os values, but not Pb and Nd isotope ratios, also deviate from the Cenozoic seawater curve towards more radiogenic values from 6.8 to 4.5 (± 0.5) Ma. However, none of the isotope systems in Fe-Mn crusts deviate from seawater at Hoss Seamount located approximately 450 km to the south. The regional gradients in isotope ratios indicate that substantial input of dissolved and particulate terrestrial material into the Monterey Canyon System is responsible for the local deviations in the seawater Nd, Pb, and Os isotope compositions from 6.8 to 4.5 (± 0.5) Ma. The isotope ratios recorded in Fe-Mn crusts are consistent with a southern Sierra Nevada or western Basin and Range provenance of the terrestrial material which was delivered by rivers to the canyon. The exhumation of the modern Monterey Canyon must have begun between 10 and 6.8 ± 0.5 Ma, as indicated by our data, the age of incised strata, and paleo-location of the Monterey Canyon relative to the paleo-coastline.
      PubDate: 2017-10-16T01:11:13.978882-05:
      DOI: 10.1002/2017GC007071
  • Using Detrital Zircon Geochronology to Constrain Paleogene Provenance and
           its Relationship to Rifting in the Zhu 1 Depression, Pearl River Mouth
           Basin, South China Sea
    • Authors: Wei Wang; Jiaren Ye, Tandis Bidgoli, Xianghua Yang, Hesheng Shi, Yu Shu
      Abstract: Paleogene syn-rift successions in the South China Sea are poorly understood and systematic provenance analysis, which could provide clues to their history, is lacking. Here we report 409 new concordant U-Pb ages from detrital zircons separated from the Paleogene Wenchang, Enping, and Zhuhai formations in the Zhu 1 depression, Pearl River Mouth Basin. The new data, combined with the published age data from the region, document changes in the provenance of syn-rift successions. Detrital zircons from the Eocene Wenchang Formation are unimodal, with Jurassic-Cretaceous (180-80 Ma) ages making up>80% of grains. The ages are consistent with the geochronology of intrabasinal highs, dominated by igneous rocks emplaced during the Yanshanian orogeny, and suggest local provenance. By contrast, detrital zircons from the upper Eocene to lower Oligocene Enping Formation form three well-recognized age-clusters, with peaks at 150 Ma, 254 Ma, and 438 Ma that match documented tectonomagmatism in South China Block (SCB). Combined with increasing numbers of Precambrian zircons, the data suggest increasing influence of regional provenance of the SCB. Similar age peaks are also recognized from the limited number of zircons analyzed from the upper Oligocene Zhuhai Formation and comparability with modern shelf and river sediment indicates the unit was mainly sourced from the SCB and likely transported by a paleo-Pearl River. We infer that the change in provenance, from local uplifts within the Zhu 1 to the SCB, is related to distinct phases of PRMB rift development; however, later changes are best explained by SCB drainage evolution.
      PubDate: 2017-10-15T19:40:26.968814-05:
      DOI: 10.1002/2017GC007110
  • 3-D Seismic Imaging of Ancient Submarine Lava Flows: An Example From the
           Southern Australian Margin
    • Authors: P. Reynolds; S. Holford, N. Schofield, A. Ross
      Abstract: Submarine lava flows are the most common surficial igneous rock on the Earth. However, they are inherently more difficult to study than their subaerial counterparts due to their inaccessibility. In this study we use newly-acquired 3D (three-dimensional) seismic reflection data to document the distribution and morphology of 26 ancient, buried lava flows within the Middle Eocene-aged Bight Basin Igneous Complex, offshore southern Australia. Many of these lava flows are associated with volcanoes that vary from 60 − 625 m in height and 0.3 − 10 km in diameter. Well data and seismic-stratigraphic relationships suggest that the lava flows and volcanoes were emplaced offshore in water depths of
      PubDate: 2017-10-03T10:30:57.403555-05:
      DOI: 10.1002/2017GC007178
  • A Hybrid Approach to Data Assimilation for Reconstructing the Evolution of
           Mantle Dynamics
    • Authors: Quan Zhou; Lijun Liu
      Abstract: Quantifying past mantle dynamic processes represents a major challenge in understanding the temporal evolution of the solid earth. Mantle convection modeling with data assimilation is one of the most powerful tools to investigate the dynamics of plate subduction and mantle convection. Although various data assimilation methods, both forward and inverse, have been created, these methods all have limitations in their capabilities to represent the real earth. Pure forward models tend to miss important mantle structures due to the incorrect initial condition and thus may lead to incorrect mantle evolution. In contrast, pure tomography-based models cannot effectively resolve the fine slab structure and would fail to predict important subduction-zone dynamic processes. Here we propose a hybrid data assimilation approach that combines the unique power of the sequential and adjoint algorithms, which can properly capture the detailed evolution of the downgoing slab and the tomographically constrained mantle structures, respectively. We apply this new method to reconstructing mantle dynamics below the western U.S. while considering large lateral viscosity variations. By comparing this result with those from several existing data assimilation methods, we demonstrate that the hybrid modeling approach recovers the realistic 4-D mantle dynamics the best.
      PubDate: 2017-10-03T10:30:42.067151-05:
      DOI: 10.1002/2017GC007116
  • Paleoproterozoic Geomagnetic Field Strength From the Avanavero Mafic
           Sills, Amazonian Craton, Brazil
    • Authors: A. Di Chiara; A. R. Muxworthy, R.I.F. Trindade, F. Bispo-Santos
      Abstract: A recent hypothesis has suggested that Earth's inner core nucleated during the Mesoproterozoic, as evidenced by a rapid increase in the paleointensity (ancient geomagnetic field intensity) record; however, paleointensity data during the Paleoproterozoic and Mesoproterozoic period are limited. To address this problem, we have determined paleointensity from samples from three Paleoproterozoic Avanavero mafic sills (Amazonian Craton, Brazil): Cotingo, 1782 Ma, Puiuà 1788, and Pedra Preta, 1795 Ma. We adopted a multi-protocol approach for paleointensity estimates combining Thellier-type IZZI and LTD-IZZI methods, and the non-heating Preisach protocol. We obtained an average VDM value of 1.3 ± 0.7 × 1022Am2 (Cotingo) of 2.0 ± 0.4 × 1022Am2 (Puiuà) and 6 ± 4 × 1022Am2 (Pedra Preta); it is argued that the Cotingo estimate is the most robust. Our results are the first data from the upper Paleoproterozoic for South America and are comparable to data available from other regions and similar periods. The new data do not invalidate the hypothesis of that Earth's inner core nucleated during the Mesoproterozoic.
      PubDate: 2017-09-29T11:46:51.426935-05:
      DOI: 10.1002/2017GC007175
  • Holocene Paleointensity of the Island of Hawai'i From Glassy Volcanics
    • Authors: G. Cromwell; F. Trusdell, L. Tauxe, H. Staudigel, H. Ron
      Abstract: This study presents new high-quality paleointensity records and 14C radiocarbon age determinations from the Island of Hawai'i during the Holocene. Previous studies on Hawai'i use experimental methods and statistical selection criteria that may produce inaccurate geomagnetic field strength estimates. Additional high-quality paleointensity results can be used to evaluate the existing Hawaiian dataset and investigate Holocene geomagnetic field behavior. New paleointensity sites from 22 lava flows were calculated using the IZZI-Thellier laboratory technique and a strict set of selection criteria. Rapidly cooled, glassy volcanic material was collected for all sites. Isotopic age determinations range from 270- > 10,000 years before present (nine new 14C ages are also presented as part of this study). The median intensity for the 22 flows is 47.5 μT, with a median absolute deviation uncertainty of 5.6 μT; substantially greater than the present day field strength at Hawai'i (∼36 μT). These new results are comparable to previously published data from this location and are consistent with global paleointensity models. There is no evidence of an intensity “spike” at 3,000 years before present, as seen in the Levant and elsewhere. Previously published data vary in intensity by experimental technique relative to data using glassy material and strict selection criteria. Non-Thellier-type data are biased low, a result of these techniques estimating intensity from possibly non-single domain magnetic carriers. Thellier-Thellier data are biased high, the reasons for which remain unclear as no cooling rate effect was demonstrated and we were unable to reproduce the high bias with different selection criteria.
      PubDate: 2017-09-29T11:46:16.303262-05:
      DOI: 10.1002/2017GC006927
  • Extracting a Detailed Magnetostratigraphy From Weakly Magnetized,
           Oligocene to Early Miocene Sediment Drifts Recovered at IODP Site U1406
           (Newfoundland Margin, Northwest Atlantic Ocean)
    • Authors: Tim E. van Peer; Chuang Xuan, Peter C. Lippert, Diederik Liebrand, Claudia Agnini, Paul A. Wilson
      Abstract: Fine-grained magnetic particles in deep-sea sediments often statistically align with the ambient magnetic field during (and shortly after) deposition and can therefore record geomagnetic reversals. Correlation of these reversals to a geomagnetic polarity time scale is an important geochronological tool that facilitates precise stratigraphic correlation and dating of geological records globally. Sediments often carry a remanence strong enough for confident identification of polarity reversals, but in some cases a low signal-to-noise ratio prevents the construction of a reliable and robust magnetostratigraphy. Here we implement a data-filtering protocol, which can be integrated with the UPmag software package, to automatically reduce the maximum angular deviation and statistically mask noisy data and outliers deemed unsuitable for magnetostratigraphic interpretation. This protocol thus extracts a clearer signal from weakly magnetized sediments recovered at Integrated Ocean Drilling Program (IODP) Expedition 342 Site U1406 (Newfoundland margin, northwest Atlantic Ocean). The resulting magnetostratigraphy, in combination with shipboard and shore-based biostratigraphy, provides an age model for the study interval from IODP Site U1406 between Chrons C6Ar and C9n (∼21-27 Ma). We identify rarely observed geomagnetic directional changes within Chrons C6Br, C7r, and C7Ar, and perhaps within Subchron C8n.1n. Our magnetostratigraphy dates three intervals of unusual stratigraphic behavior within the sediment drifts at IODP Site U1406 on the Newfoundland margin. These lithostratigraphic changes are broadly concurrent with the coldest climatic phases of the middle Oligocene to early Miocene and we hypothesize that they reflect changes in bottom-water circulation.
      PubDate: 2017-09-29T11:45:34.767422-05:
      DOI: 10.1002/2017GC007185
  • Tibetan Magmatism Database
    • Authors: James B. Chapman; Paul Kapp
      Abstract: A database containing previously published geochronologic, geochemical, and isotopic data on Mesozoic to Quaternary igneous rocks in the Himalayan-Tibetan orogenic system is presented. The database is intended to serve as a repository for new and existing igneous rock data and is publicly accessible through a web-based platform that includes an interactive map and data table interface with search, filtering, and download options. To illustrate the utility of the database, the age, location, and εHft composition of magmatism from the central Gangdese batholith in the southern Lhasa terrane are compared. The data identify three high-flux events, which peak at 93 Ma, 50 Ma, and 15 Ma. They are characterized by inboard arc migration and a temporal and spatial shift to more evolved isotopic compositions.
      PubDate: 2017-09-29T11:44:57.880911-05:
      DOI: 10.1002/2017GC007217
  • Redistribution of Iron and Titanium in High-Pressure Ultramafic Rocks
    • Authors: Rosalind J. Crossley; Katy A. Evans, Steven M. Reddy, Gregory W. Lester
      Abstract: The redox state of iron in high-pressure serpentinites, which host a significant proportion of Fe3+ in subduction zones, can be used to provide an insight into iron cycling and constrain the composition of subduction zone fluids. In this study, we use oxide and silicate mineral textures, interpretation of mineral parageneses, mineral composition data, and whole rock geochemistry of high-pressure retrogressed ultramafic rocks from the Zermatt-Saas Zone to constrain the distribution of iron and titanium, and iron oxidation state. These data provide an insight on the oxidation state and composition of fluids at depth in subduction zones. Oxide minerals host the bulk of iron, particularly Fe3+. The increase in mode of magnetite and observation of magnetite within antigorite veins in the investigated ultramafic samples during initial retrogression is most consistent with oxidation of existing iron within the samples during the infiltration of an oxidizing fluid since it is difficult to reconcile addition of Fe3+ with the known limited solubility of this species. However, high Ti contents are not typical of serpentinites and also cannot be accounted for by simple mixing of a depleted mantle protolith with the nearby Allalin gabbro. Titanium-rich phases coincide with prograde metamorphism and initial exhumation, implying the early seafloor and/or prograde addition and late mobilization of Ti. If Ti addition has occurred, then the introduction of Fe3+, also generally considered to be immobile, cannot be disregarded. We explore possible transport vectors for Ti and Fe through mineral texture analysis.
      PubDate: 2017-09-28T10:36:55.195733-05:
      DOI: 10.1002/2017GC007145
  • Spatially Variable CO2 Degassing in The Main Ethiopian Rift: Implications
           For Magma Storage, Volatile Transport And Rift-Related Emissions
    • Authors: Jonathan A. Hunt; Amdemichael Zafu, Tamsin A. Mather, David M. Pyle, Peter H. Barry
      Abstract: Deep carbon emissions from historically inactive volcanoes, hydrothermal and tectonic structures are among the greatest unknowns in the long-term (∼Myr) carbon cycle. Recent estimates of diffuse CO2 flux from the Eastern Rift of the East African Rift System (EARS) suggest this could equal emissions from the entire mid-ocean ridge system. We report new CO2 surveys from the Main Ethiopian Rift (MER, northernmost EARS), and reassess the rift-related CO2 flux. Since degassing in the MER is concentrated in discrete areas of volcanic and off-edifice activity, characterisation of such areas is important for extrapolation to a rift-scale budget. Locations of hot springs and fumaroles along the rift show numerous geothermal areas away from volcanic edifices. With these new data we estimate total CO2 emissions from the central and northern MER as 0.52—4.36 Mt yr−1. Our extrapolated flux from the Eastern Rift is 3.9—32.7 Mt yr−1 CO2, overlapping with lower end of the range presented in recent estimates. By scaling, we suggest that 6—18 Mt yr−1 CO2 flux can be accounted for by magmatic extension, which implies an important role for volatile-enriched lithosphere, crustal assimilation and/or additional magmatic intrusion to account for the upper range of flux estimates. Our results also have implications for the nature of volcanism in the MER. Many geothermal areas are found>10 km from the nearest volcanic centre, suggesting ongoing hazards associated with regional volcanism.
      PubDate: 2017-09-28T10:32:09.261285-05:
      DOI: 10.1002/2017GC006975
  • Paleomagnetic Constraints on the Middle Miocene-Early Pliocene
           Stratigraphy in the Xining Basin, NE Tibetan Plateau, and the Geologic
    • Authors: Rongsheng Yang; Xiaomin Fang, Qingquan Meng, Jinbo Zan, Weilin Zhang, Tao Deng, Yibo Yang, Xiaobai Ruan, Liye Yang, Bingshuai Li
      Abstract: The Xining Basin lies in the transitional zone between the arid Asian interior and the East Asian monsoon region. The continuous Cenozoic sediments in the basin provide a unique archive recording the uplift of the Tibetan Plateau and its environmental effects on central Asian aridification and Asian monsoon evolution. However, sediments deposited since the middle Middle Miocene have not been precisely dated, hindering our ability to address these issues. Here, we dated a 336-m-thick section containing many Late Miocene fossil mammals from the eastern basin. High-resolution paleomagnetism revealed 16 normal and 16 reversed zones that correlate well with chrons 3n to 5Ar.1r of the Geomagnetic Polarity Time Scale, constraining the section to ∼12.7-4.8 Ma. The changes in lithofacies from floodplain to braided river at ∼8.6 Ma and to thick alluvial fan at ∼6.3 Ma with predominantly southerly paleocurrent directions occur simultaneously with an increase in the sedimentation rates, representing two periods of rapid uplift in the eastern Qilian Shan to the north. Our results provide a robust oldest age constraint (
      PubDate: 2017-09-28T10:30:28.086514-05:
      DOI: 10.1002/2017GC006945
  • Morphological Expressions of Crater Infill Collapse: Model Simulations of
           Chaotic Terrains on Mars
    • Authors: Manuel Roda; George Marketos, Jan Westerweel, Rob Govers
      Abstract: Martian chaotic terrains are characterized by deeply depressed intensively fractured areas that contain a large number of low-strain tilted blocks. Stronger deformation (e.g. higher number of fractures) is generally observed in the rims when compared to the middle regions of the terrains. The distribution and number of fractures and tilted blocks are correlated with the size of the chaotic terrains. Smaller chaotic terrains are characterized by few fractures between undeformed blocks. Larger terrains show an elevated number of fractures uniformly distributed with single blocks. We investigate whether this surface morphology may be a consequence of the collapse of the infill of a crater. We perform numerical simulations with the Discrete Element Method and we evaluate the distribution of fractures within the crater and the influence of the crater size, infill thickness and collapsing depth on the final morphology.The comparison between model predictions and the morphology of the Martian chaotic terrains shows strong statistical similarities in terms of both number of fractures and correlation between fractures and crater diameters. No or very weak correlation is observed between fractures and the infill thickness or collapsing depth. The strong correspondence between model results and observations suggests that the collapse of an infill layer within a crater is a viable mechanism for the peculiar morphology of the martian chaotic terrains.
      PubDate: 2017-09-25T11:24:27.674575-05:
      DOI: 10.1002/2017GC006933
  • Great Salt Lake (Utah) Microbialite δ13C, δ18O, and δ15N Record
           Fluctuations in Lake Biogeochemistry Since the Late Pleistocene
    • Authors: D. L. Newell; J. L. Jensen, C. M. Frantz, M. D. Vanden Berg
      Abstract: Extensive lacustrine microbialite deposits exposed along the shores of Great Salt Lake (GSL), Utah preserve a rich continental paleoenvironmental record. Newly-reported microbialite carbon and oxygen stable isotope ratios in carbonate, nitrogen isotope ratios in organic matter, and organic matter radiocarbon ages archive paleolake hydrological and biogeochemical changes from the late Pleistocene through the Holocene. Positive correlations between δ18O and δ13C in ∼15 – 7.6 cal ka microbialite carbonate are consistent with a hydrologically closed-basin lake with fluctuations in volume, chemistry, and associated changes in lake primary production. The δ15N of microbialite bulk organic matter (5 – 18 ‰ vs. AIR) shows that the balance between nitrogen fixation and assimilation of dissolved inorganic nitrogen has varied significantly. Inverse δ18O and δ13C correlations in combination with high δ15N in some carbonate deposits may imply periods of higher salinity and stable lake stratification similar to modern GSL conditions. We compare our C and O datasets with Pleistocene Lake Bonneville carbonate stable isotope records and demonstrate progressive development of spatially-isolated hydrological basins during the shift to warmer and drier conditions in the Holocene.
      PubDate: 2017-09-21T11:37:36.823971-05:
      DOI: 10.1002/2017GC007078
  • Hydrothermal Venting at Hinepuia Submarine Volcano, Kermadec Arc:
           Understanding Magmatic-Hydrothermal Fluid Chemistry
    • Authors: Valerie K. Stucker; Sharon L. Walker, Cornel E. J. de Ronde, Fabio Caratori Tontini, Shinji Tsuchida
      Abstract: The Hinepuia volcanic center is made up of two distinct edifices aligned northwest to southeast, with an active cone complex in the SE. Hinepuia is one of several active volcanoes in the northern segment of the Kermadec arc. Regional magnetic data shows no evidence for large-scale hydrothermal alteration at Hinepuia, yet plume data confirm present-day hydrothermal discharge, suggesting that the hydrothermal system may be too young to have altered the host rocks with respect to measurable changes in magnetic signal. Gravity data are consistent with crustal thinning and shallow mantle under the volcanic center. Following the discovery of hydrothermal plumes over Hinepuia, the submersible Shinkai 6500 was used to explore the SE cone and sample hydrothermal fluids.The chemistry of hydrothermal fluids from submarine arc and backarc volcanoes are typically dominated by water-rock interactions and/or magmatic degassing. Chemical analyses of vent fluids show that Hinepuia does not quite fit either traditional model. Moreover, the Hinepuia samples fall between those typically ascribed to both end-member fluid types when plotted on a K-Mg-SO4 ternary diagram. Due to evidence of strong degassing, abundant native sulfur deposition, and H2S presence, the vent sampled at Hinepuia is ultimately classified as a magmatic-hydrothermal system with a water-rock influence. This vent is releasing water vapor and magmatic volatiles with a notable lack of salinity due to subcritical boiling and phase separation. Magmatic-hydrothermal fluid chemistry appears to be controlled by a combination of gas flux, phase separation processes, and volcano evolution and/or distance from the magma source.
      PubDate: 2017-09-21T11:30:45.627151-05:
      DOI: 10.1002/2016GC006713
  • Arctic Deep-Water Ferromanganese-Oxide Deposits Reflect the Unique
           Characteristics of the Arctic Ocean
    • Authors: James R. Hein; Natalia Konstantinova, Mariah Mikesell, Kira Mizell, Jessica N. Fitzsimmons, Phoebe Lam, Laramie T. Jensen, Yang Xiang, Amy Gartman, Georgy Cherkashov, Deborah R. Hutchinson, Claire P. Till
      Abstract: Little is known about marine mineral deposits in the Arctic Ocean, an ocean dominated by continental shelf and basins semi-closed to deep-water circulation. Here, we present data for ferromanganese crusts and nodules collected from the Amerasia Arctic Ocean in 2008, 2009, and 2012 (HLY0805, HLY0905, HLY1202). We determined mineral and chemical compositions of the crusts and nodules and the onset of their formation. Water column samples from the GEOTRACES program were analyzed for dissolved and particulate scandium concentrations, an element uniquely enriched in these deposits.The Arctic crusts and nodules are characterized by unique mineral and chemical compositions with atypically high growth rates, detrital contents, Fe/Mn ratios, and low Si/Al ratios, compared to deposits found elsewhere. High detritus reflects erosion of submarine outcrops and North America and Siberia cratons, transport by rivers and glaciers to the sea, and distribution by sea ice, brines, and currents. Uniquely high Fe/Mn ratios are attributed to expansive continental shelves, where diagenetic cycling releases Fe to bottom waters, and density flows transport shelf bottom water to the open Arctic Ocean. Low Mn contents reflect the lack of a mid-water oxygen minimum zone that would act as a reservoir for dissolved Mn. The potential host phases and sources for elements with uniquely high contents are discussed with an emphasis on scandium. Scandium sorption onto Fe oxyhydroxides and Sc-rich detritus account for atypically high scandium contents. The opening of Fram Strait in the Miocene and ventilation of the deep basins initiated Fe-Mn crust growth ∼15 Myr ago.
      PubDate: 2017-09-21T11:26:34.751794-05:
      DOI: 10.1002/2017GC007186
  • Light Stable Isotopic Compositions of Enriched Mantle Sources: Resolving
           the Dehydration Paradox
    • Authors: J. E. Dixon; I. N. Bindeman, R. H. Kingsley, K. K. Simons, P. J. le Roux, T. R. Hajewski, P. Swart, C. H. Langmuir, J. G. Ryan, K. J. Walowski, I. Wada, P. J. Wallace
      Abstract: Volatile and stable isotope data provide tests of mantle processes that give rise to mantle heterogeneity. New data on enriched mid-oceanic ridge basalts (MORB) show a diversity of enriched components. Pacific PREMA-type basalts (H2O/Ce = 215 ± 30, δDSMOW = -45 ± 5 ‰) are similar to those in the northern Atlantic (H2O/Ce = 220 ± 30; δDSMOW = -30 to -40 ‰). Basalts with EM-type signatures have regionally variable volatile compositions. Northern Atlantic EM-type basalts are wetter (H2O/Ce = 330 ± 30) and have isotopically heavier hydrogen (δDSMOW = -57 ± 5 ‰) than northern Atlantic MORB. Southern Atlantic EM-type basalts are damp (H2O/Ce = 120 ± 10) with intermediate δDSMOW (-68 ± 2 ‰), similar to δDSMOW for Pacific MORB. Northern Pacific EM-type basalts are dry (H2O/Ce = 110 ± 20) and isotopically light (δDSMOW = -94 ± 3 ‰).A multi-stage metasomatic and melting model accounts for the origin of the enriched components by extending the subduction factory concept down through the mantle transition zone, with slab temperature a key variable. Volatiles and their stable isotopes are decoupled from lithophile elements, reflecting primary dehydration of the slab followed by secondary rehydration, infiltration and re-equilibration by fluids derived from dehydrating subcrustal hydrous phases (e.g., antigorite) in cooler, deeper parts of the slab. Enriched mantle sources form by addition of
      PubDate: 2017-09-21T11:25:40.005031-05:
      DOI: 10.1002/2016GC006743
  • In situ Raman Raman Detection of Gas Hydrates Exposed on the Seafloor of
           the South China Sea
    • Authors: Xin Zhang; Zengfeng Du, Zhendong Luan, Xiujuan Wang, Shichuan Xi, Bing Wang, Lianfu Li, Chao Lian, Jun Yan
      Abstract: Gas hydrates are usually buried in sediments. Here, we report the first discovery of gas hydrates exposed on the seafloor of the South China Sea. The in situ chemical compositions and cage structures of these hydrates were measured at the depth of 1130 m below sea level using a Raman insertion probe (RiP-Gh) that was carried and controlled by a remotely operated vehicle (ROV) Faxian. This in situ analytical technique can avoid the physical and chemical changes associated with the transport of samples from the deep sea to the surface. Natural gas hydrate samples were analyzed at two sites. The in situ spectra suggest that the newly formed hydrate was Structure I but contains a small amount of C3H8 and H2S. Pure gas spectra of CH4, C3H8 and H2S were also observed at the SCS-SGH02 site. These data represent the first in situ proof that free gas can be trapped within the hydrate fabric during rapid hydrate formation. We provide the first in situ confirmation of the hydrate growth model for the early stages of formation of crystalline hydrates in a methane-rich seafloor environment. Our work demonstrates that natural hydrate deposits, particularly those in the early stages of formation, are not monolithic single structures but instead exhibit significant small-scale heterogeneities due to inclusions of free gas and the surrounding seawater, there inclusions also serve as indicators of the likely hydrate formation mechanism. These data also reinforce the importance of correlating visual and in situ measurements when characterizing a sampling site.
      PubDate: 2017-09-21T11:20:48.813706-05:
      DOI: 10.1002/2017GC006987
  • The Impacts of Seawater Mg/Ca and Temperature on Element Incorporation in
           Benthic Foraminiferal Calcite
    • Authors: L.J. de Nooijer; I. van Dijk, T. Toyofuku, G.J. Reichart
      Abstract: On geological timescales, oceanic [Mg2+] and [Ca2+] vary with changing rates of weathering, seafloor spreading and dolomite formation. Accurate reconstruction of the ratio between [Mg2+] and [Ca2+] in seawater (Mg/Casw), may potentially be reconstructed using foraminiferal Mg/Ca ratios. Since both temperature and seawater Mg/Ca impact foraminiferal Mg/Ca, successful reconstruction of Mg/Casw requires quantification of both these parameters independently on foraminiferal Mg/Ca, as well as their combined effect on Mg-incorporation. Here we present the combined and isolated impacts of temperature and Mg/Casw on Mg incorporation in two model species, the benthic hyaline (i.e. perforate) foraminifer Elphidium crispum and porcelaneous (i.e. miliolid) foraminifer Quinqueloculina sp. using controlled growth experiments. Specimens of these two species were kept at four different temperatures (ranging from 10 to 27°C) and three Mg/Casw's (3.4, 6.4 and 8.5 mol/mol), resulting in 12 experimental conditions. Newly grown calcite was analyzed for a number of elements (Na, Mg and Sr) by laser ablation-ICP-MS. Results show that although the Mg/Ca varied by more than an order of magnitude between species, the sensitivity of Mg incorporation with respect to temperature appeared not to be influenced by Mg/Casw. By extension, these results may also help improving accuracy in the reconstruction of past Mg/Casw based on foraminifera with contrasting Mg/Ca.
      PubDate: 2017-09-21T11:20:40.503805-05:
      DOI: 10.1002/2017GC007183
  • Stress State in the Kumano Basin and in Slope Sediment Determined From
           Anelastic Strain Recovery: Results From IODP Expedition 338 to the Nankai
    • Authors: Kiyokazu Oohashi; Weiren Lin, Hung-Yu Wu, Asuka Yamaguchi, Yuhji Yamamoto
      Abstract: Three-dimensional, in situ stresses in the Kumano Basin and slope sediment (IODP Sites C0002 and C0022) in the Nankai Trough, southwest Japan, have been determined using the anelastic strain recovery (ASR) of core samples. Two samples taken from Hole C0002J, located in the bottom of the Kumano Basin, indicate that the maximum principal stress, σ1, is vertical. The intermediate principal stress, σ2, is oriented ENE–WSW, parallel to the trench axis. These stress orientations are similar to those obtained using ASR and borehole breakout methods in previous expeditions. In contrast, a sample from the lower section of the slope sediment (Hole C0022B), located beneath the megasplay fault, is characterized by σ1 plunging moderately to the ESE and σ3 oriented near-horizontally, trending NNE–SSW. The direction of maximum horizontal stress obtained from ASR (WNW–ESE) is similar to that inferred from borehole breakouts in an adjacent hole (NW–SE). Trench-normal compression and a near-vertical σ2 are also inferred from focal mechanisms of very-low-frequency earthquakes within the Nankai accretionary prism, and from borehole breakouts in the hanging wall of the megasplay fault. These observations suggest that the horizontal compressional regime extends to a shallower level than previously thought, likely due to the shallow portion of the megasplay fault accumulating tectonic stress in response to plate convergence.
      PubDate: 2017-09-12T11:55:55.558981-05:
      DOI: 10.1002/2017GC007137
  • Investigating Segmentation in Cascadia: Anisotropic Crustal Structure and
           Mantle Wedge Serpentinization from Receiver Functions
    • Authors: Hannah E. Krueger; Erin A. Wirth
      Abstract: The Cascadia subduction zone exhibits along-strike segmentation in structure, processes, and seismogenic behavior. While characterization of seismic anisotropy can constrain deformation processes at depth, the character of seismic anisotropy in Cascadia remains poorly understood. This is primarily due to a lack of seismicity in the subducting Juan de Fuca slab, which limits shear wave splitting and other seismological analyses that interrogate the fine-scale anisotropic structure of the crust and mantle wedge. We investigate lower crustal anisotropy and mantle wedge structure by computing P-to-S receiver functions at 12 broadband seismic stations along the Cascadia subduction zone. We observe P-to-SV converted energy consistent with previously estimated Moho depths. Several stations exhibit evidence of an “inverted Moho” (i.e., a downward velocity decrease across the crust-mantle boundary), indicative of a serpentinized mantle wedge. Stations with an underlying hydrated mantle wedge appear prevalent from northern Washington to central Oregon, but sparse in southern Oregon and northern California. Transverse component receiver functions are complex, suggesting anisotropic and/or dipping crustal structure. To constrain the orientation of crustal anisotropy we compute synthetic receiver functions using manual forward modeling. We determine that the lower crust shows variable orientations of anisotropy along-strike, with highly complex anisotropy in northern Cascadia, and generally NW-SE and NE-SW orientations of slow-axis anisotropy in central and southern Cascadia, respectively. The orientations of anisotropy from this work generally agree with those inferred from shear wave splitting of tremor studies at similar locations, lending confidence to this relatively new method of inferring seismic anisotropy from slow earthquakes.
      PubDate: 2017-09-11T11:32:08.056537-05:
      DOI: 10.1002/2017GC007064
  • Extreme monsoon rainfall signatures preserved in the invasive terrestrial
           gastropod Lissachatina fulica
    • Authors: Prosenjit Ghosh; Ravi Rangarajan, Kaustubh Thirumalai, Fred Naggs
      Abstract: Indian summer monsoon (ISM) rainfall lasts for a period of four months with large variations recorded in terms of rainfall intensity during its period between June to September. Proxy reconstructions of past ISM rainfall variability are required due to the paucity of long instrumental records. However, reconstructing sub-seasonal rainfall is extremely difficult using conventional hydroclimate proxies due to inadequate sample resolution. Here, we demonstrate the utility of the stable oxygen isotope composition of gastropod shells in reconstructing past rainfall on sub-seasonal timescales. We present a comparative isotopic study on present day rainwater and stable isotope ratios of precipitate found in the incremental growth bands of giant African land snail Lissachatina fulica (Bowdich) from modern day (2009) and in the historical past (1918). Isotopic signatures present in the growth bands allowed for the identification of ISM rainfall variability in terms of its active and dry spells in the modern as well as past gastropod record. Our results demonstrate the utility of gastropod growth band stable isotope ratios in semi-quantitative reconstructions of seasonal rainfall patterns. High resolution climate records extracted from gastropod growth band stable isotopes (museum and archived specimens) can expand the scope for understanding past sub-seasonal-to-seasonal climate variability.
      PubDate: 2017-09-07T10:40:33.147307-05:
      DOI: 10.1002/2017GC007041
  • Generation of silicic melts in the early Izu-Bonin arc recorded by
           detrital zircons in proximal arc volcaniclastic rocks from the Philippine
    • Authors: A.P. Barth; K. Tani, S. Meffre, J.L. Wooden, M.A. Coble, R.J. Arculus, O. Ishizuka, J.T. Shukle
      Abstract: A 1.2 kilometer thick Paleogene volcaniclastic section at International Ocean Discovery Program Site 351-U1438 preserves the deep-marine, proximal record of Izu-Bonin oceanic arc initiation and volcano evolution along the Kyushu-Palau Ridge (KPR). Pb/U ages and trace element compositions of zircons recovered from volcaniclastic sandstones preserve a remarkable temporal record of juvenile island arc evolution. Pb/U ages ranging from 43 to 27 Ma are compatible with provenance in one or more active arc edifices of the northern KPR. The abundances of selected trace elements with high concentrations provide insight into the genesis of U1438 detrital zircon host melts, and represent useful indicators of both short and long-term variations in melt compositions in arc settings. The Site U1438 zircons span the compositional range between zircons from mid-ocean ridge gabbros and zircons from relatively enriched continental arcs, as predicted for melts in a primitive oceanic arc setting derived from a highly depleted mantle source. Melt zircon saturation temperatures and Ti-in-zircon thermometry suggest a provenance in relatively cool and silicic melts that evolved toward more Th and U-rich compositions with time. Th, U and light rare earth element enrichments beginning about 35 Ma are consistent with detrital zircons recording development of regional arc asymmetry and selective trace element-enriched rear arc silicic melts as the juvenile Izu-Bonin arc evolved.
      PubDate: 2017-09-06T16:30:33.753004-05:
      DOI: 10.1002/2017GC006948
  • Magma buoyancy and volatile ascent driving autocyclic eruptivity at Hekla
           Volcano (Iceland)
    • Authors: Stefanie Hautmann; I. Selwyn Sacks, Alan T. Linde, Matthew J. Roberts
      Abstract: Volcanic eruptions are typically accompanied by ground deflation due to the withdrawal of magma from depth and its effusion at the surface. Here, based on continuous high-resolution borehole strain data, we show that ground deformation was absent during the major effusion phases of the 1991 and 2000 eruptions of Hekla Volcano, Iceland. This lack of surface deformation challenges the classic model of magma intrusion/withdrawal as source for volcanic ground uplift/subsidence. We incorporate geodetic and geochemical observables into theoretical models of magma chamber dynamics in order to constrain quantitatively alternative co- and inter-eruptive physical mechanisms that govern magma propagation and system pressurization. We find the lack of surface deformation during lava effusion to be linked to chamber replenishment from below whilst magma migrates as a buoyancy-driven flow from the magma chamber towards the surface. We further demonstrate that inter-eruptive pressure build-up is likely to be generated by volatile ascent within the chamber rather than magma injection. Our model explains the persistent periodic eruptivity at Hekla throughout historic times with self-initiating cycles and is conceptually relevant to other volcanic systems.
      PubDate: 2017-08-31T11:40:23.341566-05:
      DOI: 10.1002/2017GC007061
  • Micro-computed tomography: Applications for high-resolution skeletal
           density determinations. An example using annually banded crustose
           coralline algae
    • Authors: P. Chan; J. Halfar, C.J.D. Norley, S.I. Pollmann, W. Adey, D.W. Holdsworth
      Abstract: Warming and acidification of the world's oceans are expected to have widespread consequences for marine biodiversity and ecosystem functioning. However, due to the relatively short record of instrumental observations, one has to rely upon geochemical and physical proxy information stored in biomineralized shells and skeletons of calcareous marine organisms as in-situ recorders of past environments. Of particular interest is the response of marine calcifiers to ocean acidification through the examination of structural growth characteristics. Here we demonstrate the application of micro-computed tomography (micro-CT) for three-dimensional visualization and analysis of growth, skeletal density, and calcification in a slow-growing, annually-banded crustose coralline alga Clathromorphum nereostratum (increment width ∼380 µm). X-ray images and time series of skeletal density were generated at 20 µm resolution and rebinned to 40, 60, 80, and 100 µm for comparison in a sensitivity analysis. Calcification rates were subsequently calculated as the product of density and growth (linear extension). While both skeletal density and calcification rates do not significantly differ at varying spatial resolutions (the latter being strongly influenced by growth rates), clear visualization of micron-scale growth features and the quantification of structural changes on subannual timescales requires higher scanning resolutions. In the present study, imaging at 20 µm resolution reveals seasonal cycles in density that correspond to summer/winter variations in skeletal structure observed using scanning electron microscopy (SEM). Micro-CT is a fast, non-destructive, and high-resolution technique for structural and morphometric analyses of temporally-banded paleoclimate archives, particularly those that exhibit slow or compressed growth or micron-scale structures.
      PubDate: 2017-08-24T11:25:37.595044-05:
      DOI: 10.1002/2017GC006966
  • Radioactive heat production of six geologically important nuclides
    • Authors: Thomas Ruedas
      Abstract: Heat production rates for the geologically important nuclides 26Al, 40K, 60Fe, 232Th, 235U, and 238U are calculated on the basis of recent data on atomic and nuclear properties. The revised data differ by several per cent from some older values, but indicate that more recent analyses converge toward values with an accuracy sufficient for all common geoscience applications, although some possibilities for improvement still remain, especially in the case of 40K and with regard to the determination of half-lives. A Python script is provided for calculating heat production (
      PubDate: 2017-08-24T11:25:25.986533-05:
      DOI: 10.1002/2017GC006997
  • Fault-magma interactions during early continental rifting: Seismicity of
           the Magadi-Natron-Manyara basins, Africa
    • Authors: A. Weinstein; S. J. Oliva, C. J. Ebinger, S. Roecker, C. Tiberi, M. Aman, C. Lambert, E. Witkin, J. Albaric, S. Gautier, S. Peyrat, J. D. Muirhead, A. N. N. Muzuka, G. Mulibo, G. Kianji, R. Ferdinand-Wambura, M. Msabi, A. Rodzianko, R. Hadfield, F. Illsley-Kemp, T.P. Fischer
      Abstract: Although magmatism may occur during the earliest stages of continental rifting, its role in strain accommodation remains weakly constrained by largely 2D studies. We analyze seismicity data from a 13-month, 39-station broadband seismic array to determine the role of magma intrusion on state-of-stress and strain localization, and their along-strike variations. Precise earthquake locations using cluster analyses and a new 3D velocity model reveal lower crustal earthquakes beneath the central basins and along projections of steep border faults that degas CO2. Seismicity forms several disks interpreted as sills at 6-10 km below a monogenetic cone field. The sills overlie a lower crustal magma chamber that may feed eruptions at Oldoinyo Lengai volcano. After determining a new ML scaling relation, we determine a b-value of 0.87 ± 0.03. Focal mechanisms for 65 earthquakes, and 13 from a catalogue prior to our array reveal an along-axis stress rotation of ∼60° in the magmatically active zone. New and prior mechanisms show predominantly normal slip along steep nodal planes, with extension directions ∼ N90°E north and south of an active volcanic chain consistent with geodetic data, and ∼ N150°E in the volcanic chain. The stress rotation facilitates strain transfer from border fault systems, the locus of early stage deformation, to the zone of magma intrusion in the central rift. Our seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Results indicate that earthquakes are largely driven by stress state around inflating magma bodies.
      PubDate: 2017-08-21T10:32:57.501624-05:
      DOI: 10.1002/2017GC007027
  • Sr-Nd-Hf-O isotope geochemistry of the Ertaibei pluton, East Junggar, NW
           China: Implications for development of crustal-scale granitoid pluton and
           crustal growth
    • Authors: Gong-Jian Tang; Qiang Wang, Chunfu Zhang, Derek A. Wyman, Wei Dan, Xiao-Ping Xia, Hong-Yi Chen, Zhen-Hua Zhao
      Abstract: To better understand the compositional diversity of plutonic complexes and crustal growth of the Central Asian Orogenic Belt (CAOB), we conducted an integrated study of the Ertaibei pluton, which obtained geochronological, petrological, geochemical, and isotopic (including whole rock Sr-Nd, in-situ zircon Hf-O) data. The pluton (ca. 300 Ma) is composed of granodiorites that contain mafic microgranular enclaves (MMEs), dolerite dikes, and granite dikes containing quartz–tourmaline orbicules. The dolerite dikes were possibly generated by melting of an asthenospheric mantle source, with discrete assimilation of lower crustal components in the MASH (melting, assimilation, storage, and homogenization) zone. The MMEs originated from hybridization between mantle- and crust-derived magmas, which spanned a range of melting depths (∼25 – 30 km) in the MASH zone and were episodically tapped. Melting of the basaltic lower crust in the core of the MASH zone generated magmas to form the granodiorites. The granite dikes originated from melting of an arc-derived volcanogenic sedimentary source with a minor underplated basaltic source in the roof of the MASH zone (∼25 km). The compositional diversity reflects both the magma sources and the degree of maturation of the MASH zone. Although having mantle-like radiogenic isotope compositions, the Ertaibei and other post-collisional granitoids show high zircon δ18O values (mostly between +6 and +9‰), indicating a negligible contribution to the CAOB crustal growth during the post-collisional period.
      PubDate: 2017-08-21T10:25:49.696052-05:
      DOI: 10.1002/2017GC006998
  • Testing a thermo-chemo-hydro-geomechanical model for gas hydrate bearing
           sediments using triaxial compression lab experiments
    • Authors: S. Gupta; C. Deusner, M. Haeckel, R. Helmig, B. Wohlmuth
      Abstract: Natural gas hydrates are considered a potential resource for gas production on industrial scales. Gas hydrates contribute to the strength and stiffness of the hydrate-bearing sediments. During gas production, the geomechanical stability of the sediment is compromised. Due to the potential geotechnical risks and process management issues, the mechanical behavior of the gas hydrate-bearing sediments needs to be carefully considered. In this study, we describe a coupling concept that simplifies the mathematical description of the complex interactions occuring during gas production by isolating the effects of sediment deformation and hydrate phase changes. Central to this coupling concept is the assumption that the soil grains form the load-bearing solid skeleton, while the gas hydrate enhances the mechanical properties of this skeleton. We focus on testing this coupling concept in capturing the overall impact of geomechanics on gas production behavior though numerical simulation of a high-pressure isotropic compression experiment combined with methane hydrate formation and dissociation. We consider a linear-elastic stress-strain relationship because it is uniquely defined and easy to calibrate. Since, in reality, the geomechanical response of the hydrate bearing sediment is typically inelastic and is characterized by a significant shear-volumetric coupling, we control the experiment very carefully in order to keep the sample deformations small and well within the assumptions of poro-elasticity. The closely co-ordinated experimental and numerical procedures enable us to validate the proposed simplified geomechanics-to-flow coupling, and set an important precursor towards enhancing our coupled hydro-geomechanical hydrate reservoir simulator with more suitable elasto-plastic constitutive models.
      PubDate: 2017-08-14T11:10:42.88686-05:0
      DOI: 10.1002/2017GC006901
  • Organic carbon preservation in Southeastern Arabian Sea sediments since
           mid-Holocene: Implications to South Asian Summer Monsoon variability
    • Authors: Siddhesh S. Nagoji; Manish Tiwari
      Abstract: The earlier studies show a contrasting long-term trend of the South Asian Summer Monsoon (SASM) after attaining the precessional forcing induced mid-Holocene maximum. The increasing total organic carbon (TOC) concentration of marine sediments in the Southeastern Arabian Sea (SEAS) has been interpreted to imply strengthening SASM since mid-Holocene by a few studies. However, TOC concentration is also influenced by redox conditions, sedimentation rate, and an influx of terrigenous matter depending on the regional settings. So, it needs to be ascertained whether the TOC concentration of the sediments in the SEAS is a signal of productivity related to the SASM strength or preservation. Therefore, we studied multiple proxies (TOC, total nitrogen, atomic C/N, δ13Corg, CaCO3, and major and trace elements concentration) for determining the productivity, redox conditions, detrital supply, and provenance in a sediment core from the upper continental slope of the SEAS spanning the past ∼4700 years at centennial scale resolution. The present study shows that the observed TOC increase is not a result of enhanced productivity but is because of better preservation due to the increased sedimentation rate along with increasingly reducing conditions since mid-Holocene. We further show that the SASM has been declining since mid-Holocene after attaining a precession-forced maximum, which corroborates the earlier model ensemble studies.
      PubDate: 2017-08-14T11:10:32.141698-05:
      DOI: 10.1002/2017GC006804
  • Geochemical and geophysical constrains on the dynamic topography of the
           Southern African Plateau
    • Authors: Alan G. Jones; Juan Carlos Afonso, Javier Fullea
      Abstract: The deep mantle African Superswell is considered to contribute to the topographic uplift of the Southern African Plateau, but dynamic support estimates vary wildly depending on the approach and data used. One reason for these large disparities is that the role of lithospheric structure, key in modulating deep dynamic contributions to elevation, is commonly ignored or oversimplified in convection studies. We use multiple high-quality geophysical data coupled with xenolith-based geochemical constraints to compute the isostatic lithospheric contribution to the elevation of the Plateau, facilitating isolation of the current dynamic component from the total observed elevation. We employ a multi-observable stochastic algorithm to invert geoid anomaly, surface-wave dispersion data, magnetotelluric data and surface heat flow to predict elevation in a fully thermodynamically and internally-consistent manner. We find that a compositionally-layered 230 ±7 km thick lithosphere is required to simultaneously fit all four data types, in agreement with abundant independent xenolith evidence. Our stochastic modelling indicates a lithospheric contribution to elevation of the order of 670 m, which implies dynamic support arising from the convecting sub-lithospheric mantle of ∼650 m. Our results have important implications for the understanding of lithospheric-deep mantle feedback mechanisms and for calibrating dynamic topography estimates from global convection studies.
      PubDate: 2017-08-14T11:10:28.18306-05:0
      DOI: 10.1002/2017GC006908
  • Trace element partitioning between plagioclase and Melt: An investigation
           of the impact of experimental and analytical procedures
    • Authors: Roger L. Nielsen; Gokce Ustunisik, Allison B. Weinsteiger, Frank J. Tepley, A. Dana Johnston, Adam J. R. Kent
      Abstract: Quantitative models of petrologic processes require accurate partition coefficients. Our ability to obtain accurate partition coefficients is constrained by their dependence on pressure temperature and composition, and on the experimental and analytical techniques we apply. The source and magnitude of error in experimental studies of trace element partitioning may go unrecognized if one examines only the processed published data. The most important sources of error are relict crystals, and analyses of more than one phase in the analytical volume. Because we have typically published averaged data, identification of compromised data is difficult if not impossible. We addressed this problem by examining unprocessed data from plagioclase/melt partitioning experiments, by comparing models based on that data with existing partitioning models, and evaluated the degree to which the partitioning models are dependent on the calibration data. We found that partitioning models are dependent on the calibration data in ways that result in erroneous model values, and that the error will be systematic and dependent on the value of the partition coefficient. In effect, use of different calibration datasets will result in partitioning models whose results are systematically biased, and that one can arrive at different and conflicting conclusions depending on how a model is calibrated, defeating the purpose of applying the models. Ultimately this is an experimental data problem, which can be solved if we publish individual analyses (not averages) or use a projection method wherein we use an independent compositional constraint to identify and estimate the uncontaminated composition of each phase.
      PubDate: 2017-08-12T10:37:01.423971-05:
      DOI: 10.1002/2017GC007080
  • Directional change during a Miocene R-N geomagnetic polarity reversal
           recorded by mafic lava flows, Sheep Creek Range, north central Nevada, USA
    • Authors: S. W. Bogue; J. M. G. Glen, N. A. Jarboe
      Abstract: Recurring transitional field directions during three Miocene geomagnetic reversals provide evidence that lateral inhomogeneity of the lower mantle affects flow in the outer core. We compare new paleomagnetic results from a composite sequence of 15.2 Ma lava flows in north central Nevada (Sheep Creek Range; 40.7N, 243.2E), erupted during a polarity reversal, to published data from Steens Mountain (250 km to the northwest in Oregon) and the Newberry Mountains (650 km to the south in California) that document reversals occurring millions of years and many polarity switches earlier. Alternating field demagnetization, followed by thermal demagnetization in half the samples, clearly isolated the primary thermoremanent magnetization of Sheep Creek Range flows. We correlated results from our three sampled sections to produce a composite record that begins with a single virtual geomagnetic pole (VGP) at low latitude in the Atlantic, followed by two VGPs situated near latitude 30N in NE Africa. After jumping to 83N (one VGP), the pole moves to equatorial South America (one VGP), back to NE Africa (three VGPs), to high southern latitudes (two VGPs), back to equatorial South America (three VGPs), and finally to high northern latitudes (nine VGPs). The repeated visits of the transitional VGP to positions in South America and near NE Africa, as well as the similar behavior recorded at Steens Mountain and the Newberry Mountains, suggest that lower mantle or core-mantle boundary features localize core flow structures, thereby imparting a discernible regional structure on the transitional geomagnetic field that persists for millions of years.
      PubDate: 2017-08-12T10:36:44.741208-05:
      DOI: 10.1002/2017GC007049
  • Influence of static alternating field demagnetization on anisotropy of
           magnetic susceptibility: Experiments and implications
    • Authors: Andrea R. Biedermann; Mike Jackson, Dario Bilardello, Joshua M. Feinberg, Maxwell C. Brown, Suzanne A. McEnroe
      Abstract: Anisotropy of magnetic susceptibility (AMS) indicates the preferred orientation of a rock's constituent minerals. However, other factors can influence the AMS, e.g. domain wall pinning or domain alignment in ferromagnetic minerals. Therefore, it is controversial whether samples should be alternating field (AF) demagnetized prior to AMS characterization. This may remove the influence of natural remanent magnetization (NRM) or domain wall pinning on AMS; however, it may also result in field-induced anisotropy. This study investigates the influence of stepwise AF and low-temperature demagnetization on mean susceptibility, principal susceptibility directions, AMS degree and shape for sedimentary, metamorphic and igneous rocks. Alternating fields up to 200 mT were applied along the sample x, y and z axes, rotating the order for each step, to characterize the relationship between AMS principal directions and the last AF orientation. The changes in anisotropy, defined by the mean deviatoric susceptibility of the difference tensors, are between
      PubDate: 2017-08-12T10:36:40.957782-05:
      DOI: 10.1002/2017GC007073
  • Thermal segmentation of mid-ocean ridge transform faults
    • Authors: Monica Wolfson-Schwehr; Margaret S. Boettcher, Mark D. Behn
      Abstract: 3D finite element simulations are used to calculate thermal structures and mantle flow fields underlying mid-ocean ridge transform faults (RTFs) composed of two fault segments separated by an orthogonal step-over. Using fault lengths and slip rates, we derive an empirical scaling relation for the critical step-over length (LS∼), which marks the transition from predominantly horizontal to predominantly vertical mantle flow at the base of the lithosphere under a step-over. Using the ratio of step-over length (LS) to LS∼, we define 3 degrees of segmentation: first-degree, corresponding to type I step-overs (LS/LS∼ ≥ 3); second-degree, corresponding to type II step-overs (1 ≤ LS/LS∼ 
      PubDate: 2017-08-12T10:36:09.238745-05:
      DOI: 10.1002/2017GC006967
  • Heat flow bounds over the Cascadia margin derived from bottom simulating
           reflectors and implications for thermal Models of subduction
    • Authors: Benjamin J. Phrampus; Robert N. Harris, Anne M. Tréhu
      Abstract: Understanding the thermal structure of the Cascadia subduction zone is important for understanding megathrust earthquake processes and seismogenic potential. Currently our understanding of the thermal structure of Cascadia is limited by a lack of high spatial resolution heat flow data and by poor understanding of thermal processes such as hydrothermal fluid circulation in the subducting basement, sediment thickening and dewatering, and frictional heat generation on the plate boundary. Here, using a dataset of publically available seismic lines combined with new interpretations of bottom simulating reflector (BSR) distributions, we derive heat flow estimates across the Cascadia margin. Thermal models that account for hydrothermal circulation predict BSR-derived heat flow bounds better than purely conductive models, but still over-predict surface heat flows. We show that when the thermal effects of in-situ sedimentation and of sediment thickening and dewatering due to accretion are included, models with hydrothermal circulation become consistent with our BSR-derived heat flow bounds.
      PubDate: 2017-08-12T10:35:47.815267-05:
      DOI: 10.1002/2017GC007077
  • A comparison of cooling- and volume-limited flow systems: Examples from
           channels in the Piton de la Fournaise April 2007 lava flow field
    • Authors: Maéva Rhéty; Andrew Harris, Nicolas Villeneuve, Lucia Gurioli, Etienne Médard, Oryaëlle Chevrel, Patrick Bachélery
      Abstract: Channel-fed lava flow systems lack detailed thermal and textural studies through the boundary between channelized and dispersed flow, and out to the flow front. Here, chemical, textural and morphological analyses were made to define cooling and crystallisation rates down the entire system, especially through the zone of dispersed flow. We compare two channel systems active during the 2007 eruption of Piton de la Fournaise, one of which was cooling-limited and one of which as volume-limited. In the cooling-limited case, rapid changes in rheology occurred across the zone of dispersed flow, where viscosity increased from 1000 to 1600 Pa s over the last 100 m of the channel system. This was due to an increase in cooling rate from 7°C km−1 over the first 500 m of the system, to 42°C km−1 over the last 100 m, and an increase in microcryst content from 13% to 25%. In the volume-limited case, the exponentially increasing segment of the down flow cooling and viscosity trend is absent. Instead, lava arriving at the flow front is still relatively hot (1161°C compared with a near-vent temperature of 1167°C), and is thus of relatively low viscosity (1125 Pa s). In the volume-limited case, because the channel was still in extension when supply to the system was cut, the zone of dispersed flow was extremely short. However, because lava behind the stalled flow front was still hot and fluid, break-outs from the static front resulted in a complex flow front morphology.
      PubDate: 2017-07-21T11:20:48.713077-05:
      DOI: 10.1002/2017GC006839
  • Link between Indian monsoon rainfall and physical erosion in the Himalayan
           system during the Holocene
    • Authors: Ronan Joussain; Zhifei Liu, Christophe Colin, Stéphanie Duchamp-Alphonse, Zhaojie Yu, Eva Moréno, Léa Fournier, Sébastien Zaragosi, Arnaud Dapoigny, Laure Meynadier, Franck Bassinot
      Abstract: Mineralogical and geochemical analyses conducted on cores located on the active channel-levee system of the northern Bengal Fan are used to establish changes in the weathering pattern and the sediment transport of the Himalayan system, and evaluate the effect of Indian summer monsoon rainfall during the Holocene. Our data indicate that during the Holocene, sediments from the northern Bengal Fan originate mainly from the G-B river system without any significant changes in the relative contribution of these rivers. From 9.8 to around 6 ka, relatively low smectite/(illite+chlorite) ratios and relatively high K/Si* ratios indicate high physical denudation rates of the Himalayan highlands together with a rapid transfer of the detrital material to the Bengal Fan. The period between 9.2 and 7 ka is associated to lower values of K/Si* and corresponds to the maximum of Indian monsoon rainfall which indicates a more important chemical weathering material that rapidly transits by the G-B river system without a long storage in the Indo-Gangetic plain. From 6.0 ka to present day, higher smectite/(illite+chlorite) ratio and lower K/Si* ratio document a gradual increase of sediments originated from the Indo-Gangetic plain, characterized by higher degree of chemical weathering. During the last 2.5 ka, the drastic increase in the smectite/(illite+chlorite) ratio could be associated to enhanced alteration of the plain soils due to anthropogenic activity. The comparison of mineralogical and geochemical data with previous reconstructions of the Indian monsoon dynamic indicates a rapid response of erosion and sediment transfer of the G-B river system to changes of monsoon rainfall intensity.
      PubDate: 2017-07-21T11:20:33.915601-05:
      DOI: 10.1002/2016GC006762
  • Modeling phase separation and phase change for magma ocean solidification
    • Authors: C.-E. Boukaré; Y. Ricard
      Abstract: Just after accretion, the Earth's mantle was significantly molten by the heat dissipation due to large impacts and to the segregation of the core. The mineralogical observations and thermodynamics models of solid-liquid equilibrium of silicates show that several types of crystallization may have happened at different depths in the mantle. Solids were probably formed first at the bottom of the lower mantle or at mid mantle leaving two possible magma oceans, a shallow one and an abyssal one. Near the bottom of the mantle, the liquid phase might become denser than solids due to iron enrichment. In the shallow magma ocean, the crystallizing solid phase was denser and sank through the magma to settle and compact at depth. To understand these complex dynamics, we develop a two phase numerical code that can handle simultaneously convection in each phase and in the slurry, and the compaction or decompaction of the two phases. Although our code can only run in a parameter range (Rayleigh number, viscosity contrast between phases, Prandlt number) far from what would be realistic, we think it already provides a rich dynamics that illustrates what could have happened. We show situations in which the crystallization front is gravitationally stable and situations were the newly formed solids are gravitationally unstable and can snow across the magma. Our study suggests that the location of a density contrast between solid and magma must be considered of equal importance with that of the intersection between liquidus and isentrope for what concerns mantle solidification.
      PubDate: 2017-07-15T03:23:53.619128-05:
      DOI: 10.1002/2017GC006902
  • Flexural isostasy of the carbonate platform in North central Florida
    • Authors: H. B. Woo; M. Panning, Peter N. Adams, A. Dutton
      Abstract: Deformed marine terraces can be used to explore a region's uplift history. Trail Ridge is a marine terrace in north Florida that is nearly 80 meters above modern sea level and contains Quaternary marine fossils, a fact that is inconsistent with estimates of paleo-sea level history since the early Pleistocene. This implies that the terrace has experienced uplift since its formation, as well as non-uniform deformation recorded by the warping of its previously horizontal state. The Florida carbonate platform, located on the passive margin of eastern North America, is a setting where non-tectonic influences (e.g. isostatic adjustment, dynamic topography) can be examined. We present a single-transect, numerical model of vertical displacement, derived from elastic flexure, to assess the influence of karst-driven isostatic uplift on present day topography of Trail Ridge in north Florida. Flexural modeling predicts elevations in central Florida not observed today, most likely because surface erosion and karst cavity collapse have obliterated this high topography. Older subsurface stratigraphic units, however, display the arched profile predicted from flexural modeling. Mass loss, calculated by differencing modeled topography and observed topography, was found to be 6.75 × 1012 kg, since emplacement of Trail Ridge. Uplift rates, assuming karst-driven flexural isostasy alone, using previously estimated ages of Trail Ridge of 0.125, 1.4, 3, or 3.5 Ma were found to be 0.535, 0.048, 0.022, and 0.019 mm/yr, respectively. A more likely explanation of uplift includes contributions from dynamic topography and glacial isostatic adjustment which should be further explored with more advanced geophysical modeling.
      PubDate: 2017-06-15T17:20:39.694771-05:
      DOI: 10.1002/2017GC006934
  • The Gondou hydrothermal field in the Ryukyu Arc: A huge hydrothermal
           system on the flank of a caldera volcano
    • Authors: H. Minami; Y. Ohara
      Abstract: High-resolution geophysical mapping was conducted from an autonomous underwater vehicle on the flank of Daisan-Kume Knoll in the Ryukyu Arc, southwest of Japan. 1-m resolution bathymetry identified 264 spires, 173 large mounds and 268 small mounds within a depression that is up to 1600 m wide and up to 60 m deep, at water depths between 1330 and 1470 m. Hydrothermal venting is strongly inferred from the observation of plumes in sidescan sonar imagery and positive temperature anomalies over the spires and mounds. This field, named the Gondou Field, has a giant mound G1 with a diameter of 280 m and a height of 80 m. Mound G1 has distinctive summit ridges comprised of multiple spires where acoustic plumes with temperature anomalies up to 1.12°C are observed, indicative of high-temperature venting. Other than mound G1, a number of active large mounds more than 30 m wide and spires over 10-22 m tall are common and they concentrate in the central and southern areas of the field, suggesting that these areas are the center of present hydrothermal activity. Acoustic plumes imaged by side-scan sonar at the Gondou Field are different in character from bubble plumes imaged in other hydrothermal fields in the Ryukyu Arc. The plumes are diffused and deflected as they rise through the water column and have a shape consistent with black smokers.
      PubDate: 2017-05-30T11:36:43.696855-05:
      DOI: 10.1002/2017GC006868
  • Issue Information
    • Pages: 3269 - 3269
      PubDate: 2017-10-16T05:29:05.572364-05:
      DOI: 10.1002/ggge.21125
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