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  Subjects -> PHYSICS (Total: 764 journals)
    - ELECTRICITY AND MAGNETISM (8 journals)
    - MECHANICS (20 journals)
    - NUCLEAR PHYSICS (44 journals)
    - OPTICS (91 journals)
    - PHYSICS (554 journals)
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    - THERMODYNAMICS (29 journals)

PHYSICS (554 journals)            First | 1 2 3 4 5 6 | Last

Doklady Physics     Hybrid Journal   (Followers: 1)
Dynamical Properties of Solids     Full-text available via subscription  
ECS Journal of Solid State Science and Technology     Full-text available via subscription   (Followers: 1)
Egyptian Journal of Remote Sensing and Space Science     Open Access   (Followers: 5)
EJNMMI Physics     Open Access  
Embedded Systems Letters, IEEE     Hybrid Journal   (Followers: 18)
Energy Procedia     Open Access   (Followers: 3)
Engineering Failure Analysis     Hybrid Journal   (Followers: 28)
Engineering Fracture Mechanics     Hybrid Journal   (Followers: 18)
Environmental Fluid Mechanics     Hybrid Journal   (Followers: 2)
EPJ Nonlinear Biomedical Physics     Open Access  
EPJ Quantum Technology     Open Access  
EPJ Techniques and Instrumentation     Full-text available via subscription  
EPJ Web of Conferences     Open Access  
European Journal of Physics     Full-text available via subscription   (Followers: 5)
European Journal of Physics Education     Open Access   (Followers: 5)
European Physical Journal - Applied Physics     Full-text available via subscription   (Followers: 5)
European Physical Journal C     Hybrid Journal  
Europhysics News     Open Access   (Followers: 1)
Experimental Mechanics     Hybrid Journal   (Followers: 16)
Experimental Methods in the Physical Sciences     Full-text available via subscription  
Experimental Techniques     Hybrid Journal   (Followers: 31)
Exploration Geophysics     Hybrid Journal   (Followers: 3)
Few-Body Systems     Hybrid Journal  
Fire and Materials     Hybrid Journal   (Followers: 5)
Flexible Services and Manufacturing Journal     Hybrid Journal   (Followers: 1)
Fluctuation and Noise Letters     Hybrid Journal   (Followers: 1)
Fluid Dynamics     Hybrid Journal   (Followers: 5)
Fortschritte der Physik/Progress of Physics     Hybrid Journal  
Frontiers in Physics     Open Access   (Followers: 2)
Frontiers of Materials Science     Hybrid Journal   (Followers: 4)
Frontiers of Physics     Hybrid Journal   (Followers: 1)
Fusion Engineering and Design     Hybrid Journal   (Followers: 2)
Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 22)
Geografiska Annaler, Series A: Physical Geography     Hybrid Journal   (Followers: 3)
Geophysical Research Letters     Full-text available via subscription   (Followers: 50)
Geoscience and Remote Sensing, IEEE Transactions on     Hybrid Journal   (Followers: 20)
Glass Physics and Chemistry     Hybrid Journal   (Followers: 2)
Granular Matter     Hybrid Journal   (Followers: 2)
Graphs and Combinatorics     Hybrid Journal   (Followers: 6)
Handbook of Geophysical Exploration: Seismic Exploration     Full-text available via subscription  
Handbook of Metal Physics     Full-text available via subscription  
Handbook of Surface Science     Full-text available via subscription   (Followers: 3)
Handbook of Thermal Analysis and Calorimetry     Full-text available via subscription  
Haptics, IEEE Transactions on     Hybrid Journal   (Followers: 4)
Heat Transfer - Asian Research     Hybrid Journal   (Followers: 7)
High Energy Density Physics     Hybrid Journal   (Followers: 1)
High Pressure Research: An International Journal     Hybrid Journal   (Followers: 1)
IEEE Journal of Quantum Electronics     Hybrid Journal   (Followers: 15)
IEEE Signal Processing Magazine     Full-text available via subscription   (Followers: 30)
IET Optoelectronics     Hybrid Journal   (Followers: 2)
Il Colle di Galileo     Open Access  
Indian Journal of Biochemistry and Biophysics (IJBB)     Open Access   (Followers: 4)
Indian Journal of Physics     Hybrid Journal   (Followers: 4)
Indian Journal of Pure & Applied Physics (IJPAP)     Open Access   (Followers: 8)
Indian Journal of Radio & Space Physics (IJRSP)     Open Access   (Followers: 6)
Industrial Electronics, IEEE Transactions on     Hybrid Journal   (Followers: 11)
Industry Applications, IEEE Transactions on     Hybrid Journal   (Followers: 5)
Infinite Dimensional Analysis, Quantum Probability and Related Topics     Hybrid Journal  
InfraMatics     Open Access  
Infrared Physics & Technology     Hybrid Journal  
Intelligent Transportation Systems Magazine, IEEE     Full-text available via subscription   (Followers: 1)
Intermetallics     Hybrid Journal   (Followers: 6)
International Applied Mechanics     Hybrid Journal   (Followers: 2)
International Geophysics     Full-text available via subscription   (Followers: 3)
International Journal for Computational Methods in Engineering Science and Mechanics     Hybrid Journal   (Followers: 8)
International Journal for Ion Mobility Spectrometry     Hybrid Journal   (Followers: 1)
International Journal for Simulation and Multidisciplinary Design Optimization     Full-text available via subscription   (Followers: 1)
International Journal of Abrasive Technology     Hybrid Journal   (Followers: 2)
International Journal of Aeroacoustics     Full-text available via subscription   (Followers: 6)
International Journal of Applied Electronics in Physics & Robotics     Open Access   (Followers: 1)
International Journal of Astronomy and Astrophysics     Open Access   (Followers: 3)
International Journal of Computational Materials Science and Surface Engineering     Hybrid Journal   (Followers: 7)
International Journal of Damage Mechanics     Hybrid Journal   (Followers: 5)
International Journal of Fatigue     Hybrid Journal   (Followers: 8)
International Journal of Fracture     Hybrid Journal   (Followers: 9)
International Journal of Geometric Methods in Modern Physics     Hybrid Journal   (Followers: 1)
International Journal of Geophysics     Open Access   (Followers: 3)
International Journal of Heat and Fluid Flow     Hybrid Journal   (Followers: 10)
International Journal of Low Radiation     Hybrid Journal  
International Journal of Low-Carbon Technologies     Open Access   (Followers: 1)
International Journal of Mass Spectrometry     Hybrid Journal   (Followers: 11)
International Journal of Material Forming     Hybrid Journal   (Followers: 2)
International Journal of Materials and Product Technology     Hybrid Journal   (Followers: 4)
International Journal of Mechanical Sciences     Hybrid Journal   (Followers: 5)
International Journal of Mechanics and Materials in Design     Hybrid Journal   (Followers: 5)
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology     Open Access   (Followers: 4)
International Journal of Micro-Nano Scale Transport     Full-text available via subscription   (Followers: 2)
International Journal of Microstructure and Materials Properties     Hybrid Journal   (Followers: 7)
International Journal of Microwave Science and Technology     Open Access   (Followers: 2)
International Journal of Modeling, Simulation, and Scientific Computing     Hybrid Journal   (Followers: 1)
International Journal of Modern Physics A     Hybrid Journal   (Followers: 2)
International Journal of Modern Physics B     Hybrid Journal   (Followers: 1)
International Journal of Modern Physics C     Hybrid Journal   (Followers: 1)
International Journal of Modern Physics D     Hybrid Journal   (Followers: 1)
International Journal of Modern Physics E     Hybrid Journal   (Followers: 2)
International Journal of Nanomanufacturing     Hybrid Journal   (Followers: 1)
International Journal of Nanoscience     Hybrid Journal   (Followers: 1)
International Journal of Nanotechnology     Hybrid Journal   (Followers: 5)
International Journal of Non-Linear Mechanics     Hybrid Journal   (Followers: 4)

  First | 1 2 3 4 5 6 | Last

Journal Cover Geochemistry, Geophysics, Geosystems     [SJR: 2.156]   [H-I: 61]
   [24 followers]  Follow    
   Full-text available via subscription Subscription journal
   ISSN (Online) 1525-2027
   Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • New Geophysical Constraints on a Failed Subduction Initiation: The
           Structure and Potential Evolution of the Gagua Ridge and Huatung Basin
    • Authors: Daniel H. Eakin; Kirk D. McIntosh, H. J. A. Van Avendonk, Luc Lavier
      Pages: n/a - n/a
      Abstract: We modeled the velocity structure of the Huatung Basin and Gagua Ridge using offshore wide‐angle seismic data along four ∼E‐W transects. These transects are accompanied by several multichannel seismic reflection (MCS) profiles that highlight the shallow deformation in this area east of Taiwan. Although it is agreed that the Gagua Ridge was the product of a transient compressional episode in the past, relatively few data have been collected that reveal the deeper structure resulting from this enigmatic process. The velocity models show evidence for normal, to thin, oceanic crustal thicknesses in the Huatung Basin and West Philippine Basin. Moho reflections from the associated MCS profiles confirm the thickness observed in the velocity models. The velocity models indicate significant crustal thickening associated with the Gagua Ridge, to 12‐18km along its entire length. Most importantly, the two central velocity models also show a significant asymmetry in the crustal thickening suggesting a westward underthrusting of >20km of WPB oceanic crust beneath that of the Huatung Basin. This geometry is extremely unexpected given interpretations that indicate the Huatung Basin could be significantly older than the West Philippine Basin (Early Cretaceous vs. Eocene). Our observations, along with recent geophysical data concerning the age of the Huatung Basin, indicate that the Gagua Ridge was the result of a failed subduction event during the Miocene that may have existed simultaneously and for a short time, competed with the Manila subduction zone to the west in accommodating convergence between the Eurasia and Philippine Sea plates. In this scenario, the present day Gagua Ridge represents a snapshot of a failed subduction initiation preserved in the geologic record. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-22T16:07:13.152925-05:
      DOI: 10.1002/2014GC005548
       
  • Time scales of intraoceanic arc magmatism from combined U‐Th and
           (U‐Th)/He zircon geochronology of Dominica, Lesser Antilles
    • Authors: Howe T.M; Schmitt A.K, Lindsay J.M, Shane P, Stockli D.F.
      Pages: n/a - n/a
      Abstract: The island of Dominica, located in the intra‐oceanic Lesser Antilles arc, has produced a series of intermediate (mostly andesitic) lava domes and ignimbrites since the early Pleistocene. (U‐Th)/He eruption ages from centres across the island range from ca. 3 ka to ca. 770 ka, with at least 10 eruptions occurring in the last 80 ka. Three eruptions occurred near the southern tip of Dominica (Plat Pays Volcanic Complex) in the past 15 ka alone. Zircon U‐Th ages from individual centres range from near‐eruption to secular equilibrium implicating protracted storage and recycling of zircons within the crust. Overlapping zircon crystallization peaks within deposits from geographically separated vents (up to 40km apart) indicate that magma associated with separate volcanic edifices crystallized zircon contemporaneously. Two lava domes from the southern sector of the island display exclusively young zircon rim ages (
      PubDate: 2015-01-20T17:39:17.582388-05:
      DOI: 10.1002/2014GC005636
       
  • Intraplate volcanism at the edges of the Colorado Plateau sustained by a
           combination of triggered edge‐driven convection and
           shear‐driven upwelling
    • Authors: Maxim D. Ballmer; Clinton P. Conrad, Eugene I. Smith, Racheal Johnsen
      Pages: n/a - n/a
      Abstract: Although volcanism in the southwestern United States has been studied extensively, its origin remains controversial. Various mechanisms such as mantle plumes, upwelling in response to slab sinking, and small‐scale convective processes have been proposed, but have not been evaluated within the context of rapidly shearing asthenosphere that is thought to underlie this region. Using geodynamic models that include this shear, we here explore spatio‐temporal patterns of mantle melting and volcanism near the Colorado Plateau. We show that the presence of viscosity heterogeneity within an environment of asthenospheric shearing can give rise to decompression melting along the margins of the Colorado Plateau. Our models indicate that eastward shear flow can advect pockets of anomalously low viscosity toward the edges of thickened lithosphere beneath the plateau, where they can induce decompression melting in two ways. First, the arrival of the pockets critically changes the effective viscosity near the plateau to trigger small‐scale edge‐driven convection. Second, they can excite shear‐driven upwelling (SDU), in which horizontal shear flow becomes redirected upward as it is focused within the low‐viscosity pocket. We find that a combination of “triggered” edge‐driven convection and SDU can explain volcanism along the margins of the Colorado Plateau, its encroachment toward the plateau's southwestern edge, and the association of volcanism with slow seismic anomalies in the asthenosphere. Geographic patterns of intraplate volcanism in regions of vigorous asthenospheric shearing may thus directly mirror viscosity heterogeneity of the sublithospheric mantle. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-20T17:38:31.131061-05:
      DOI: 10.1002/2014GC005641
       
  • Slip‐rate‐dependent melt extraction at oceanic transform
           faults
    • Authors: Hailong Bai; Laurent G. J. Montési
      Pages: n/a - n/a
      Abstract: Crustal thickness differences between oceanic transform faults and associated mid‐ocean ridges may be explained by melt migration and extraction processes. Slow‐slipping transform faults exhibit more positive gravity anomalies than the adjacent spreading centers, indicating relative thin crust in the transform domain, whereas at intermediate‐ and fast‐spreading ridges, transform faults are characterized by more negative gravity anomalies than the adjacent spreading centers, indicating thick crust in the transform domain. We present numerical models reproducing these observations and infer that melt can be extracted at fast‐slipping transforms, but not at slow‐slipping ones. Melt extraction is modeled as a three‐step process [Montési et al., 2011]. 1) Melt moves vertically through buoyancy‐driven porous flow enhanced by sub‐vertical dissolution channels. 2) Melt accumulates in and travels along a decompaction channel lining a low‐permeability barrier at the base of the thermal boundary layer. 3) Melt is extracted to the surface when it enters a melt extraction zone. A melt extraction width of 2 – 4km and a melt extraction depth of 15 – 20km are needed to fit the tectonic damages associated with oceanic plate boundaries that reach into the upper mantle. Our conclusions are supported by the different degrees of magmatic activities exhibited at fast‐ and slow‐slipping transforms as reflected in geological features, geochemical signals and seismic behaviors. We also constrain that the maximum lateral distance of crust‐level dike propagation is about 50 to 70km. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-20T17:37:51.280279-05:
      DOI: 10.1002/2014GC005579
       
  • Issue Information
    • Pages: i - i
      PubDate: 2015-01-16T07:59:13.561551-05:
      DOI: 10.1002/ggge.20328
       
  • Full vector low‐temperature magnetic measurements of geologic
           materials
    • Authors: Joshua M. Feinberg; Peter A. Solheid, Nicholas L. Swanson‐Hysell, Mike J. Jackson, Julie A. Bowles
      Pages: n/a - n/a
      Abstract: The magnetic properties of geologic materials offer insights into an enormous range of important geophysical phenomena ranging from inner core dynamics to paleoclimate. Often it is the low‐temperature behavior (
      PubDate: 2015-01-14T03:50:11.699045-05:
      DOI: 10.1002/2014GC005591
       
  • Ocean Basalt Simulator version 1 (OBS1): Trace element mass balance in
           adiabatic melting of a pyroxenite‐bearing peridotite
    • Authors: Jun‐Ichi Kimura; Hiroshi Kawabata
      Pages: n/a - n/a
      Abstract: We present a new numerical trace element mass balance model for adiabatic melting of a pyroxenite‐bearing peridotite for estimating mantle potential temperature, depth of melting column, and pyroxenite fraction in the source mantle for a primary ocean basalt/picrite. The Ocean Basalt Simulator version 1 (OBS1) uses a thermodynamic model of adiabatic melting of a pyroxenite‐bearing peridotite with experimentally/thermodynamically parameterized liquidus–solidus intervals and source mineralogy. OBS1 can be used to calculate a sequence of adiabatic melting with two melting models, including (1) melting of peridotite and pyroxenite sources with simple mixing of their fractional melts (melt–melt mixing model), and (2) pyroxenite melting, melt metasomatism in the host peridotite, and melting of the metasomatized peridotite (source–metasomatism model). OBS1 can be used to explore (1) the fractions of peridotite and pyroxenite, (2) mantle potential temperature, (3) pressure of termination of melting, (4) degree of melting, and (5) residual mode of the sources. In order to constrain these parameters, the model calculates a mass balance for 26 incompatible trace elements in the sources and in the generated basalt/picrite. OBS1 is coded in an Excel spreadsheet and runs with VBA macros. Using OBS1, we examine the source compositions and conditions of the mid‐oceanic ridge basalts, Loihi–Koolau basalts in the Hawaiian hotspot, and Jurassic Shatsky Rise and Mikabu oceanic plateau basalts and picrites. The OBS1 model shows the physical conditions, chemical mass balance, and amount of pyroxenite in the source peridotite, which are keys to global mantle recycling. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-14T03:25:30.729522-05:
      DOI: 10.1002/2014GC005606
       
  • Confocal Raman microscopy in sclerochronology: A powerful tool to
           visualize environmental information in recent and fossil biogenic archives
           
    • Authors: Lars Beierlein; Gernot Nehrke, Thomas Brey
      Pages: n/a - n/a
      Abstract: Biological hard‐parts and skeletons of aquatic organisms often archive information of past environmental conditions. Deciphering such information forms an essential contribution to our understanding of past climate conditions and thus our ability to mitigate the climatic, ecological and social impacts of a rapidly changing environment. Several established techniques enable the visualization and reliable use of the information stored in anatomical features of such biogenic archives, i.e., its growth patterns. Here, we test whether confocal Raman microscopy (CRM) is a suitable method to reliably identify growth patterns in the commonly used archive Arctica islandica and the extinct species Pygocardia rustica (both Bivalvia). A modern A. islandica specimen from Norway has been investigated to verify the general feasibility of CRM, resulting in highly correlated standardized growth indices (r > 0.96; P < 0.0001) between CRM derived measurements and measurements derived from the established methods of fluorescence microscopy and Mutvei's solution staining. This demonstrates the general suitability of CRM as a method for growth pattern evaluation and cross‐dating applications. Moreover, CRM may be of particular interest for paleo‐environmental reconstructions, as it yielded superior results in the analysis of fossil shell specimens (A. islandica and P. rustica) compared to both Mutvei staining and fluorescence microscopy. CRM is a reliable and valuable tool to visualize internal growth patterns in both modern and fossil calcium carbonate shells that notably also facilitates the assessment of possible diagenetic alteration prior to geochemical analysis without geochemically compromising the sample. We strongly recommend the CRM approach for the visualization of growth patterns in fossil biogenic archives, where conventional methods fail to produce useful results. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-09T06:52:20.898977-05:
      DOI: 10.1002/2014GC005547
       
  • Lithospheric structure across the California Continental Borderland from
           receiver functions
    • Authors: Zachary Reeves; Vedran Lekić, Nicholas Schmerr, Monica Kohler, Dayanthie Weeraratne
      Pages: n/a - n/a
      Abstract: Due to its complex history of deformation, the California Continental Borderland provides an interesting geological setting for studying how the oceanic and continental lithosphere responds to deformation. We map variations in present‐day lithospheric structure across the region using Ps and Sp receiver functions at permanent stations of the Southern California Seismic Network as well as ocean bottom seismometer (OBS) data gathered by the Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment (ALBACORE), which enhances coverage of the borderland and provides first direct constraints on the structure of the Pacific plate west of the Patton Escarpment. Noisiness of OBS data makes strict handpicking and bandpass filtering necessary in order to obtain interpretable receiver functions. Using H‐κ and common‐conversion point stacking, we find pronounced lithospheric differences across structural blocks, which we interpret as indicating that the Outer Borderland has been translated with little to no internal deformation, while the Inner Borderland underwent significant lithospheric thinning, most likely related to accommodating the 90 clockwise rotation of the Western Transverse Range block. West of the Patton Escarpment, we find that the transition to typical oceanic crustal thickness takes place over a lateral distance of ∼ 50km. We detect an oceanic seismic lithosphere‐asthenosphere transition at 58km depth west of the Patton Escarpment, consistent with only weak age‐dependence of the depth to the seismic lithosphere‐asthenosphere transition. Sp common conversion point stacks confirm wholesale lithospheric thinning of the Inner Borderland and suggest the presence of a slab fragment beneath the Outer Borderland. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-08T15:13:34.327624-05:
      DOI: 10.1002/2014GC005617
       
  • Radial fast‐neutron fluence gradients during rotating 40Ar/39Ar
           sample irradiation recorded with metallic fluence monitors and geological
           age standards
    • Authors: Daniel Rutte; Jörg A. Pfänder, Michal Koleška, Raymond Jonckheere, Sepp Unterricker
      Pages: n/a - n/a
      Abstract: Characterizing the neutron‐irradiation parameter J is one of the major uncertainties in 40Ar/39Ar dating. The associated uncertainty of the individual J‐value for a sample of unknown age depends on the accuracy of the age of the geological standards, the fast‐neutron fluence distribution in the reactor and the distances between standards and samples during irradiation. While it is generally assumed that rotating irradiation evens out radial neutron fluence gradients, we observed axial and radial variations of the J‐values in sample irradiations in the rotating channels of two reactors. To quantify them, we included three‐dimensionally distributed metallic fast‐ (Ni) and thermal‐ (Co) neutron fluence monitors in three irradiations and geological age standards in three more. Two irradiations were carried out under Cd‐shielding in the FRG1 reactor in Geesthacht, Germany, and four without Cd‐shielding in the LVR‐15 reactor in Řež, Czech Republic. The 58Ni(nf,p)58Co activation reaction and γ‐spectrometry of the 811 keV peak associated with the subsequent decay of 58Co to 58Fe allow one to calculate the fast‐neutron fluence. The fast‐neutron fluences at known positions in the irradiation container correlate with the J‐values determined by mass‐spectrometric 40Ar/39Ar measurements of the geological age standards. Radial neutron fluence gradients are up to 1.8%/cm in FRG1 and up to 2.2%/cm in LVR‐15; the corresponding axial gradients are up to 5.9 and 2.1%/cm. We conclude that sample rotation might not always suffice to meet the needs of high‐precision dating and gradient monitoring can be crucial. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T12:05:56.419572-05:
      DOI: 10.1002/2014GC005611
       
  • Gulf of Alaska continental slope morphology: Evidence for recent trough
           mouth fan formation
    • Authors: John M. Swartz; Sean P. S. Gulick, John A. Goff
      Pages: n/a - n/a
      Abstract: Glaciated continental shelves are host to numerous morphologic features that help understand past glacier dynamics. Southeastern Alaska is home to the St. Elias mountains, an active orogen that also hosts temperate marine glaciers. During glacial periods ice streams advance across the continental shelf, carving shelf‐crossing troughs that reach the shelf edge. We use high‐resolution multi‐beam data to develop the relationship between the Yakutat and Alsek Sea Valleys and the resulting continental slope morphology. The shelf and slope geomorphology can be divided into statistical groupings that relate to the relative balance of erosion and deposition. Our analysis indicates that only the Yakutat system has been able to build an incipient trough‐mouth fan. The extreme sediment supply from this region was able to overwhelm the steep initial topography of the transform margin, while further to the east sediment slope‐bypass dominates. This analysis provides an extreme end member to existing studies of temperate glaciation along continental margins. The unique interplay between rapid uplift due to ongoing collision and the massive erosion caused by temperate glaciers provides for sedimentary flux far above most other systems. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T09:58:33.957443-05:
      DOI: 10.1002/2014GC005594
       
  • Submarine record of volcanic island construction and collapse in the
           Lesser Antilles arc: First scientific drilling of submarine volcanic
           island landslides by IODP Expedition 340
    • Authors: Le Friant A; Ishizuka O, Boudon G, Palmer M.R, Talling P.J, Villemant B, Adachi T, Aljahdali M, Breitkreuz C, Brunet M, Caron B, Coussens M, Deplus C, Endo D, Feuillet N, Fraas A.J, Fujinawa A, Hart M.B, Hatfield R.G, Hornbach M, Jutzeler M, Kataoka K. S, Komorowski J‐C, Lebas E, Lafuerza S, Maeno F, Manga M, Martínez‐Colón M, McCanta M, Morgan S, Saito T, Slagle A, Sparks S, Stinton A, Stroncik N, Subramanyam K. S.V, Tamura Y, Trofimovs J, Voight B, Wall‐Palmer D, Wang F, Watt S.F.L.
      Pages: n/a - n/a
      Abstract: IODP Expedition 340 successfully drilled a series of sites offshore Montserrat, Martinique and Dominica in the Lesser Antilles from March to April 2012. These are among the few drill sites gathered around volcanic islands, and the first scientific drilling of large and likely tsunamigenic volcanic island‐arc landslide deposits. These cores provide evidence and tests of previous hypotheses for the composition and origin of those deposits. Sites U1394, U1399, and U1400 that penetrated landslide deposits recovered exclusively seafloor‐sediment, comprising mainly turbidites and hemipelagic deposits, and lacked debris avalanche deposits. This supports the concepts that i/ volcanic debris avalanches tend to stop at the slope break, and ii/ widespread and voluminous failures of pre‐existing low‐gradient seafloor sediment can be triggered by initial emplacement of material from the volcano. Offshore Martinique (U1399 and 1400), the landslide deposits comprised blocks of parallel strata that were tilted or micro‐faulted, sometimes separated by intervals of homogenized sediment (intense shearing), while Site U1394 offshore Montserrat penetrated a flat‐lying block of intact strata. The most likely mechanism for generating these large‐scale seafloor‐sediment failures appears to be propagation of a decollement from proximal areas loaded and incised by a volcanic debris avalanche. These results have implications for the magnitude of tsunami generation. Under some conditions, volcanic island landslide deposits comprised of mainly seafloor sediment will tend to form smaller magnitude tsunamis than equivalent volumes of subaerial block‐rich mass flows rapidly entering water. Expedition 340 also successfully drilled sites to access the undisturbed record of eruption fallout layers intercalated with marine sediment which provide an outstanding high‐resolution dataset to analyze eruption and landslides cycles, improve understanding of magmatic evolution as well as offshore sedimentation processes. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-06T00:41:56.426968-05:
      DOI: 10.1002/2014GC005652
       
  • Decadal‐scale variations in geomagnetic field intensity from ancient
           Cypriot slag mounds
    • Authors: Ron Shaar; Lisa Tauxe, Erez Ben‐Yosef, Vasiliki Kassianidou, Brita Lorentzen, Joshua M. Feinberg, Thomas E. Levy
      Pages: n/a - n/a
      Abstract: Geomagnetic models based on direct observations since the 1830s show that the averaged relative change in field intensity on Earth's surface over the past 170 years is less than 4.8% per decade. It is unknown if these rates represent the typical behavior of secular variations due to insufficient temporal resolution of archaeomagnetic records from earlier periods. To address this question we investigate two ancient slag mounds in Cyprus ‐ Skouriotissa Vouppes (SU1, 4th ‐ 5th centuries CE, 21 meter in height), and Mitsero Kokkinoyia (MK1, 7th ‐ 5th BCE, 8 meter in height). The mounds are multi‐layered sequences of slag and charcoals that accumulated near ancient copper production sites. We modeled the age‐height relation of the mounds using radiocarbon dates, and estimated paleointensities using Thellier‐type IZZI experiments with additional anisotropy, cooling rate, and non‐linear TRM assessments. To screen out ambiguous paleointensity interpretations we applied strict selection criteria at the specimen/sample levels. To ensure objectivity, consistency, and robust error estimation we employed an automatic interpretation technique and put the data available in the MagIC database. The analyses yielded two independent sub‐century scale paleointensity time series. The MK1 data indicate relatively stable field at the time the mound accumulated. In contrast, the SU1 data demonstrate changes that are comparable in magnitude to the fastest changes inferred from geomagnetic models. We suggest that fast changes observed in the published archaeomagnetic data from the Levant are driven by two longitudinally‐paired regions, the Middle East and South Africa, that show unusual activity in geomagnetic models. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-05T05:15:35.657671-05:
      DOI: 10.1002/2014GC005455
       
  • Bulk particle size distribution and magnetic properties of
           particle‐sized fractions from loess and paleosol samples in Central
           Asia
    • Authors: Jinbo Zan; Xiaomin Fang, Shengli Yang, Maodu Yan
      Pages: n/a - n/a
      Abstract: Recent studies demonstrate that particle size separation based on gravitational settling and detailed rock magnetic measurements of the resulting fractionated samples constitutes an effective approach to evaluating the relative contributions of pedogenic and detrital components in the loess and paleosol sequences on the Chinese Loess Plateau. So far, however, similar work has not been undertaken on the loess deposits in Central Asia. In this paper, seventeen loess and paleosol samples from three representative loess sections in Central Asia were separated into four grain size fractions and then systematic rock magnetic measurements were made on the fractions. Our results demonstrate that the content of the 75 μm) exhibits the minimum values of χ, χARM and SIRM, demonstrating that the concentrations of ferrimagnetic grains are not positively correlated with the bulk particle size in the Central Asian loess deposits. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-02T01:17:40.689603-05:
      DOI: 10.1002/2014GC005616
       
  • Paleolatitudes of the Tibetan Himalaya from primary and secondary
           magnetizations of Jurassic to Lower Cretaceous sedimentary rocks
    • Authors: Wentao Huang; Douwe J.J. van Hinsbergen, Mark J. Dekkers, Eduardo Garzanti, Guillaume Dupont‐Nivet, Peter C. Lippert, Xiaochun Li, Marco Maffione, Cor G. Langereis, Xiumian Hu, Zhaojie Guo, Paul Kapp
      Pages: n/a - n/a
      Abstract: The Tibetan Himalaya represents the northernmost continental unit of the Indian plate that collided with Asia in the Cenozoic. Paleomagnetic studies on the Tibetan Himalaya can help constrain the dimension and paleogeography of ‘Greater India', the Indian plate lithosphere that subducted and underthrusted below Asia after initial collision. Here, we present a paleomagnetic investigation of a Jurassic (limestones) and Lower Cretaceous (volcaniclastic sandstones) section of the Tibetan Himalaya. The limestones yielded positive fold test, showing a pre‐folding origin of the isolated remanent magnetizations. Detailed paleomagnetic analyses, rock magnetic tests, end‐member modeling of acquisition curves of isothermal remanent magnetization, and petrographic investigation reveal that the magnetic carrier of the Jurassic limestones is authigenic magnetite, whereas the dominant magnetic carrier of the Lower Cretaceous volcaniclastic sandstones is detrital magnetite. Our observations lead us to conclude that the Jurassic limestones record a prefolding remagnetization, whereas the Lower Cretaceous volcaniclastic sandstones retain a primary remanence. The volcaniclastic sandstones yield an Early Cretaceous paleolatitude of 55.5°S [52.5°S, 58.6°S] for the Tibetan Himalaya, suggesting it was part of the Indian plate at that time. The size of ‘Greater India' during Jurassic time cannot be estimated from these limestones. Instead, a paleolatitude of the Tibetan Himalaya of 23.8°S [21.8°S, 26.1°S] during the remagnetization process is suggested. It is likely that the remagnetization, caused by the oxidation of early diagenetic pyrite to magnetite, was induced during 103‐83 Ma or 77‐67 Ma. The inferred paleolatitudes at these two time intervals imply very different tectonic consequences for the Tibetan Himalaya. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-30T02:17:17.696434-05:
      DOI: 10.1002/2014GC005624
       
  • Precessional changes in the western equatorial Pacific hydroclimate: A 240
           kyr marine record from the Halmahera Sea, East Indonesia
    • Authors: Haowen Dang; Zhimin Jian, Catherine Kissel, Franck Bassinot
      Pages: n/a - n/a
      Abstract: Within the precession band, an inter‐hemispheric anti‐phase pattern in the tropical hydro‐climate is supported by many paleo‐records, and optimally explained by the forcing of precessional insolation change. However, scenarios within the western equatorial Pacific (WEP), which plays the role of the ascending center of atmospheric convection, remain poorly determined. In this study, a marine sediment core from the Halmahera Sea, East Indonesia, was analyzed with high‐resolution XRF scanning, quantitative discrete XRF and ICP‐AES/MS measurements. The terrigenous fractions in this core are constrained by their trace elemental characteristics to be locally sourced from Halmahera Island, and hence reflect variations in the local riverine runoff and precipitation. On this basis, a continuous record of precipitation changes of the western equatorial Pacific was reconstructed with multi‐decadal resolution over the last ~240 ka, using an age model established by the correlation between an adjusted ice volume model and benthic δ18O constrained by 14C dating. The records of terrigenous input show a dominant ~23 kyr periodicity with a 90°~100° phase lag to the boreal summer (i.e., in‐phase with the boreal autumn) insolation change. This pattern can be explained by the variability in the convective activity over the WEP, which might be primarily controlled by precessional changes in the El Niño and Southern Oscillation (ENSO) system. A dynamic linkage is implied between the precessional variations in the convective activity in the WEP and the East Asian and Australia‐Indonesian summer monsoons (EASM and AISM), in the sense of their distinct stable phase relationship to precession. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-29T02:38:47.764371-05:
      DOI: 10.1002/2014GC005550
       
  • A 3‐D Lagrangian finite element algorithm with remeshing for
           simulating large‐strain hydrodynamic instabilities in power law
           viscoelastic fluids
    • Authors: M. von Tscharner; S. M. Schmalholz
      Pages: n/a - n/a
      Abstract: We present a three‐dimensional (3‐D) numerical algorithm (PINK‐3D) that is based on the finite element method. The algorithm is designed to simulate hydrodynamic instabilities in power‐law viscoelastic fluids under gravity. These instabilities are caused by large and sharp contrasts in mechanical strength and/or density between different materials (e.g. folding, necking or Rayleigh‐Taylor diapirism). The instabilities are controlled by the geometry of the material interfaces and the related intra‐layer stress distribution when amplitudes of the material interfaces are still low. The presented algorithm combines a deformable Lagrangian mesh with re‐meshing in order to accurately simulate the low‐amplitude stages of the emerging instabilities, and also to simulate the large strain evolution of the structures emerging from these instabilities. The re‐meshing is based on material interfaces that accurately track the boundaries between materials with strongly varying material properties (e.g. effective viscosity or power‐law stress exponent). We describe here the main technical details of the 3‐D algorithm. The accuracy of the 3‐D algorithm is demonstrated with comparisons between the numerical results and 2‐D and 3‐D analytical solutions for folding, necking, Rayleigh‐Taylor diapirism and circular inclusions in viscous medium. We also benchmark the 3‐D algorithm with results of a different 2‐D finite element algorithm to test the accuracy of the large strain results with re‐meshing. Furthermore, two tests are presented that show the accuracy of the viscoelasticity implementation. PINK‐3D is also used to study 3‐D necking applied to lithospheric slab detachment, and 2‐D and 3‐D folding applied to fold nappe formation. In particular, we apply the 3‐D code to quantify and visualize the evolution of the 3‐D finite strain ellipsoid for the developing 3‐D structures. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-29T01:41:41.00192-05:0
      DOI: 10.1002/2014GC005628
       
  • Oxygen isotope thermometry, speedometry, and hygrometry: apparent
           equilibrium temperature versus closure temperature
    • Authors: Huaiwei Ni
      Pages: n/a - n/a
      Abstract: Rather than indicating formation/peak temperature, oxygen isotope fractionations preserved in mineral assemblages of slowly cooled plutonic and metamorphic rocks yield apparent equilibrium temperatures (Tae). The isotopic fractionations and Tae values deliver information about cooling history, as the extent of diffusive exchange of oxygen isotopes during cooling is controlled by the cooling time scale or cooling rate. Despite that several models, such as the Fast Grain Boundary (FGB) model, have been developed to simulate oxygen isotope exchange between coexisting minerals during cooling, extraction of cooling rate remains far from straightforward. On the other hand, there is a well‐defined quantitative relationship between the Dodson closure temperature (Tc) and the cooling rate, but Tc cannot be directly measured. Based on simulation results of existing models for a variety of rock systems, including open systems (with an infinite fluid reservoir), closed systems (with negligible fluid participation) and semi‐open systems (with moderate fluid participation), this study demonstrates that Tae of the mineral pair with the largest equilibrium isotope fractionation (PLEIF) is always bounded by their Tc values, regardless of how mineral proportions vary or how significant a role fluid has played in isotopic exchange. If the two Tc values happen to be similar, Tae will serve as a good approximation of both Tc, provided that the equilibrium fractionation factor has been precisely determined as a function of temperature. One such pair is quartz‐magnetite. By contrast, a mineral pair with similar Tc but relatively small fractionation is susceptible to the disturbance from other minerals, hence does not always have Tae confined within their Tc range. The relationship of Tae‐Tc correspondence for PLEIF with similar Tc can be used to constrain either cooling rate (i.e., as a speedometry method) or oxygen isotope diffusivity if one of them has been independently determined. In the latter case, the inferred oxygen diffusivity may be an index of water fugacity (i.e., as a hygrometry method) when compared with experimental diffusivity values measured under different fluid conditions. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-19T20:50:04.0963-05:00
      DOI: 10.1002/2014GC005574
       
  • Magmatic plumbing at Lucky Strike volcano based on olivine‐hosted
           melt inclusion compositions
    • Authors: V.D. Wanless; A.M. Shaw, M.D. Behn, S.A. Soule, J. Escartín, C. Hamelin
      Pages: n/a - n/a
      Abstract: Here we present volatile, major and trace element concentrations of 64 olivine‐hosted melt inclusions from the Lucky Strike segment on the mid‐Atlantic ridge. Lucky Strike is one of two locations where a crustal melt lens has been seismically imaged on a slow‐spreading ridge. Vapor‐saturation pressures, calculated from CO2 and H2O contents of Lucky Strike melt inclusions, range from approximately 300–3000 bars, corresponding to depths of 0.5–9.9 km below the seafloor. Approximately 50% of the melt inclusions record crystallization depths of 3–4 km, corresponding to the seismically‐imaged melt lens depth, while an additional ~35% crystallize at depths > 4 km. This indicates that while crystallization is focused within the melt lens, significant crystallization also occurs in the lower crust and/or upper mantle. The melt inclusions span a range of major and trace element concentrations from normal to enriched basalts. Trace element ratios at all depths are heterogeneous, suggesting that melts are not efficiently homogenized in the mantle or crust, despite the presence of a melt lens. This is consistent with the transient nature of magma chambers proposed for slower‐spreading ridges. To investigate the petrogenesis of the melt inclusion compositions, we compare the measured trace element compositions to theoretical melting calculations that consider variations in the melting geometry and heterogeneities in the mantle source. The full range of compositions can be produced by slight variations in the proportion of an Azores plume and depleted upper mantle components and changes in the total extent of melting. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-19T20:49:54.113663-05:
      DOI: 10.1002/2014GC005517
       
  • Thermodynamic calculations of the polybaric melting phase relations of
           spinel lherzolite
    • Authors: Kenta Ueki; Hikaru Iwamori
      Pages: n/a - n/a
      Abstract: This study presents a new thermodynamic model for the calculation of phase relations during the melting of anhydrous spinel lherzolite at pressures of 1–2.5 GPa. The model is based on the total energy minimization algorithm for calculating phase equilibria within multicomponent systems and the thermodynamic configuration of Ueki and Iwamori [2013]. The model is based on a SiO2 – Al2O3 – FeO–Fe3O4–MgO–CaO system that includes silicate melt, olivine, clinopyroxene, orthopyroxene, and spinel as possible phases. The molar Gibbs free energy of the melt phase is modeled quasi‐empirically, and the thermodynamic parameters for silicate melt end‐member components are calibrated with a polybaric calibration database. The temperatures and pressures used in this newly compiled calibration dataset are 1230–1600∘C and 0.9–3 GPa, corresponding to the stability range of spinel lherzolite. The modeling undertaken during this study reproduces the general features of experimentally determined melting phase relations of spinel lherzolite at 1–2.5 GPa, including the solidus temperature, the melt composition, the chemical reaction during melting and the degree of melting. This new thermodynamic modeling also reproduces phase relations of various bulk compositions from fertile to deplete spinel lherzolite and can be used in the modeling of polybaric mantle melting within various natural settings. Comparing the results derived from this new modeling with those produced using previous models indicates that the new approach outlined here, involving a combination of total energy minimization and the direct calibration of melt thermodynamic parameters at pressure and temperature conditions corresponding to mantle melting with a relatively simple melt thermodynamic equation, can accurately model polybaric melting phase relations. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-16T14:55:58.637236-05:
      DOI: 10.1002/2014GC005546
       
  • Mechanical properties and processes of deformation in shallow sedimentary
           rocks from subduction zones: An experimental study
    • Authors: Leslie Gadenne; Hugues Raimbourg, Rémi Champallier, Yuzuru Yamamoto
      Pages: n/a - n/a
      Abstract: To better constrain the mechanical behavior of sediments accreted to accretionary prism, we conducted triaxial mechanical tests on natural samples from the Miura‐Boso paleo‐accretionary prism (Japan) in drained conditions with confining pressures up to 200 MPa as well as post‐experiments P‐wave velocity (Vp) measurements. During experiments, deformation is principally non‐coaxial and accommodated by two successive modes of deformation, both associated with strain‐hardening and velocity‐strengthening behavior: (1) compaction‐assisted shearing, distributed in a several mm‐wide shear zone and (2) faulting, localized within a few tens of µm‐wide, dilatant fault zone. Deformation is also associated with (1) a decrease in Young's modulus all over the tests, (2) anomalously low Vp in the deformed samples compared to their porosity and (3) an increase in sensitivity of Vp to effective pressure. We interpret this evolution of the poroelastic properties of the material as reflecting the progressive breakage of intergrain cement and the formation of microcracks along with macroscopic deformation. When applied to natural conditions, these results suggest that the deformation style (localized vs distributed) of shallow (z 
      PubDate: 2014-12-13T02:40:55.456707-05:
      DOI: 10.1002/2014GC005580
       
  • Toward a unified hydrous olivine electrical conductivity law
    • Authors: Emmanuel Gardés; Fabrice Gaillard, Pascal Tarits
      Pages: n/a - n/a
      Abstract: It has long been proposed that water incorporation in olivine has dramatic effects on the upper mantle properties, affecting large scale geodynamics and triggering high electrical conductivity. But the laboratory‐based laws of olivine electrical conductivity predict contrasting effects of water, precluding the interpretation of geophysical data in term of mantle hydration. We review the experimental measurements of hydrous olivine conductivity and conclude that most of data are consistent when errors in samples water contents are considered. We report a new law calibrated on the largest database of measurements on hydrous olivine oriented single crystals and polycrystals. It fits most of measurements within uncertainties, and is compatible with most of geophysical data within petrological constraints on mantle olivine hydration. The isotropic conductivity (S/m) is where CH2O is the water concentration in olivine (wt.ppm) and T the temperature (K). The conductivity anisotropy of hydrous olivine might be higher than dry olivine, but preferential orientation should produce moderate anisotropy (~0–0.8 log unit). In the oceanic mantle, the enhancement of olivine conductivity is limited to ~1 log unit in the maximum range of mantle olivine water concentrations (0–500 wt.ppm). Strongest enhancements are expected in colder regions, like cratonic lithospheres and subduction settings. High conductivities in melt‐free mantle require great depths and high water concentrations in olivine (>0.1 S/m at >250 km and >200 wt.ppm). Thus, the hydration of olivine appears unlikely to produce the highest conductivities of the upper mantle. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-09T04:30:13.61405-05:0
      DOI: 10.1002/2014GC005496
       
  • Effects of crystal shape and size modality on magma rheology
    • Authors: P. Moitra; H. M. Gonnermann
      Pages: n/a - n/a
      Abstract: Erupting magma often contains crystals over a wide range of sizes and shapes, potentially affecting magma viscosity over many orders of magnitude. A robust relation between viscosity and the modality of crystal sizes and shapes remains lacking, principally because of the dimensional complexity and size of the governing parameter space. We have performed a suite of shear viscosity measurements on liquid‐particle suspensions of dynamical similarity to crystal‐bearing magma. Our experiments encompass five suspension types, each consisting of unique mixtures of two different particle sizes and shapes. The experiments span two orthogonal subspaces of particle concentration, as well as particle size and shape for each suspension type, thereby providing insight into the topology of parameter space. For each suspension type, we determined the dry maximum packing fraction and measured shear rates across a range of applied shear stresses. The results were fitted using a Herschel‐Bulkley model and augment existing predictive capabilities. We demonstrate that our results are consistent with previous work, including friction‐based constitutive laws for granular materials. We conclude that predictions for ascent rates of crystal‐rich magmas must take the shear‐rate dependence of viscosity into account. Shear‐rate dependence depends first and foremost on the volume fraction of crystals, relative to the maximum packing fraction, which in turn depends on crystal size and shape distribution. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-04T10:41:07.359378-05:
      DOI: 10.1002/2014GC005554
       
  • Ages and magnetic structures of the South China Sea constrained by deep
           tow magnetic surveys and IODP Expedition 349
    • Authors: Chun‐Feng Li; Xing Xu, Jian Lin, Xing Xu, Zhen Sun, Jian Zhu, Yongjian Yao, Xixi Zhao, Qingsong Liu, Denise K. Kulhanek, Jian Wang, Taoran Song, Junfeng Zhao, Ning Qiu, Yongxian Guan, Zhiyuan Zhou, Trevor Williams, Rui Bao, Anne Briais, Elizabeth A. Brown, Yifeng Chen, Peter D. Clift, Frederick S. Colwell, Kelsie A. Dadd, Weiwei Ding, Iván Hernández Almeida, Xiao‐Long Huang, Sangmin Hyun, Tao Jiang, Anthony A.P. Koppers, Qianyu Li, Chuanlian Liu, Zhifei Liu, Renata H. Nagai, Alyssa Peleo‐Alampay, Xin Su, Maria Luisa (Marissa) G. Tejada, Hai Son Trinh, Yi‐Ching Yeh, Chuanlun Zhang, Fan Zhang, Guo‐Liang Zhang
      Pages: n/a - n/a
      Abstract: Combined analyses of deep tow magnetic anomalies and International Ocean Discovery Program Expedition 349 cores show that initial seafloor spreading started around 33 Ma in the northeastern South China Sea (SCS), but varied slightly by 1‐2 myr along the northern continent‐ocean boundary (COB). A southward ridge jump of ∼ 20km occurred around 23.6 Ma in the East Subbasin; this timing also slightly varied along the ridge and was coeval to the onset of seafloor spreading in the Southwest Subbasin, which propagated for about 400km southwestward from ∼23.6 Ma to ∼ 21.5 Ma. The terminal age of seafloor spreading is ∼15 Ma in the East Subbasin and ∼16 Ma in the Southwest Subbasin. The full spreading rate in the East Subbasin varied largely from ∼20 to ∼80km/myr, but mostly decreased with time except for the period between ∼26.0 Ma and the ridge jump (∼23.6 Ma), within which the rate was the fastest at ∼70km/myr on average. The spreading rates are not correlated, in most cases, to magnetic anomaly amplitudes that reflect basement magnetization contrasts. Shipboard magnetic measurements reveal at least one magnetic reversal in the top 100m of basaltic layers, in addition to large vertical intensity variations. These complexities are caused by late‐stage lava flows that are magnetized in a different polarity from the primary basaltic layer emplaced during the main phase of crustal accretion. Deep tow magnetic modeling also reveals this smearing in basement magnetizations by incorporating a contamination coefficient of 0.5, which partly alleviates the problem of assuming a magnetic blocking model of constant thickness and uniform magnetization. The primary contribution to magnetic anomalies of the SCS is not in the top 100m of the igneous basement. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-04T10:25:15.58005-05:0
      DOI: 10.1002/2014GC005567
       
  • MELTS_Excel: A Microsoft Excel‐based MELTS interface for research
           and teaching of magma properties and evolution
    • Authors: Guilherme A. R. Gualda; Mark S. Ghiorso
      Pages: n/a - n/a
      Abstract: The thermodynamic modeling software MELTS is a powerful tool for investigating crystallization and melting in natural magmatic systems. Rhyolite‐MELTS is a recalibration of MELTS that better captures the evolution of silicic magmas in the upper crust. The current interface of rhyolite‐MELTS, while flexible, can be somewhat cumbersome for the novice. We present a new interface that uses web services consumed by a VBA backend in Microsoft Excel©. The interface is contained within a macro‐enabled workbook, where the user can insert the model input information and initiate computations that are executed on a central server at OFM Research. Results of simple calculations are shown immediately within the interface itself. It is also possible to combine a sequence of calculations into an evolutionary path; the user can input starting and ending temperatures and pressures, temperature and pressure steps, and the prevailing oxidation conditions. The program shows partial updates at every step of the computations; at the conclusion of the calculations, a series of data sheets and diagrams are created in a separate workbook, which can be saved independently of the interface. Additionally, the user can specify a grid of temperatures and pressures and calculate a phase diagram showing the conditions at which different phases are present. The interface can be used to apply the rhyolite‐MELTS geobarometer. We demonstrate applications of the interface using an example early‐erupted Bishop Tuff composition. The interface is simple to use and flexible, but it requires an internet connection. The interface is distributed for free from http://melts.ofm‐research.org. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-04T10:24:41.015814-05:
      DOI: 10.1002/2014GC005545
       
  • Long‐term evolution of an Oligocene/Miocene maar lake from Otago,
           New Zealand
    • Authors: B. R. S. Fox; J. Wartho, G. S. Wilson, D. E. Lee, F. E. Nelson, U. Kaulfuss
      Pages: n/a - n/a
      Abstract: Foulden Maar is a highly resolved maar lake deposit from the South Island of New Zealand comprising laminated diatomite punctuated by numerous diatomaceous turbidites. Basaltic clasts found in debris flow deposits near the base of the cored sedimentary sequence yielded two new 40Ar/39Ar dates of 24.51 ± 0.24 Ma and 23.38 ±. 24 Ma (2σ). The younger date agrees within error with a previously published 40Ar/39Ar date of 23.17 ± 0.19 Ma from a basaltic dyke adjacent to the maar crater. The diatomite is inferred to have been deposited over several tens of thousands of years in the latest Oligocene/earliest Miocene, and may have been coeval with the period of rapid glaciation and subsequent deglaciation of Antarctica known as the Mi‐1 event. Sediment magnetic properties and SEM measurements indicate that the magnetic signal is dominated by pseudo‐single domain pyrrhotite. The most likely source of detrital pyrrhotite is schist country rock fragments from the inferred tephra ring created by the phreatomagmatic eruption that formed the maar. Variations in magnetic mineral concentration indicate a decrease in erosional input throughout the depositional period, suggesting long‐term (tens of thousands of years) environmental change in New Zealand in the latest Oligocene/earliest Miocene. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-04T10:24:05.397549-05:
      DOI: 10.1002/2014GC005534
       
  • Magmatic arc structure around Mount Rainier, WA, from the joint inversion
           of receiver functions and surface wave dispersion
    • Authors: Mathias Obrebski; Geoffrey A. Abers, Anna Foster
      Pages: n/a - n/a
      Abstract: The deep magmatic processes in volcanic arcs are often poorly understood. We analyze the shear wave velocity (VS) distribution in the crust and uppermost mantle below Mount Rainier, in the Cascades arc, resolving the main velocity contrasts based on converted phases within P coda via source normalization or receiver function (RF) analysis. To alleviate the trade‐off between depth and velocity we use long period phase velocities (25‐100s) obtained from earthquake surface waves, and at shorter period (7‐21s) use seismic noise cross‐correlograms. We use a transdimensional Bayesian scheme to explore the model space (VS in each layer, number of interfaces and their respective depths, level of noise on data). We apply this tool to 15 broadband stations from permanent and EarthScope temporary stations. Most results fall into 2 groups with distinctive properties. Stations east of the arc (Group I) have comparatively slower middle‐to‐lower crust (VS=3.4‐3.8km/s at 25km depth), a sharp Moho and faster uppermost mantle (VS=4.2‐4.4km/s). Stations in the arc (Group II) have a faster lower crust (VS=3.7‐4km/s) overlying a slower uppermost mantle (VS=4.0‐4.3km/s), yielding a weak Moho. Lower crustal velocities east of the arc (Group I) most likely represent ancient subduction mélanges mapped nearby. The lower crust for Group II ranges from intermediate to felsic. We propose that intermediate‐felsic to felsic rocks represent the pre‐arc basement, while intermediate composition indicates the mushy andesitic crustal magmatic system plus solidified intrusion along the volcanic conduits. We interpret the slow upper mantle as partial melt. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-04T10:22:01.469927-05:
      DOI: 10.1002/2014GC005581
       
  • Chalcophile behavior of thallium during MORB melting and implications for
           the sulfur content of the mantle
    • Authors: Sune G. Nielsen; Nobumichi Shimizu, Cin‐Ty A. Lee, Mark D. Behn
      Pages: n/a - n/a
      Abstract: We present new laser ablation ICPMS trace element concentration data for 28 elements in 97 mid ocean ridge basalt (MORB) glasses that cover all major spreading centers as well as Tl concentration data for all mineral phases in five lherzolites from the Lherz massif, France. The ratio between the elements thallium (Tl) and cerium (Ce) is nearly constant in MORB, providing evidence that the depleted MORB mantle (DMM) has uniform Ce/Tl. Lherzolite mineral data reveal that sulfides are heterogeneous and contain between 23 and 430ng/g of Tl while all other minerals contain Tl below the analytical detection limit of ∼1ng/g. We argue that Tl in MORB is controlled by residual sulfide during mantle melting. To investigate the observed relationship between Tl and Ce, we conduct models of fractional mantle melting, which show that the constant Ce/Tl in MORB is only reproduced if the ratio between clinopyroxene and sulfide in the upper mantle varies by less than 10%. In addition, the rate of melting for these two phases must be nearly identical as otherwise melt depletion and refertilization processes would lead to Ce/Tl fractionation. These model results allow us to establish a relationship for the sulfur content of DMM: [S]DMM = SCSS × Mcpx ⁄Rcpx, where SCSS is the sulfur concentration of a silicate melt at sulfide saturation, Rcpx is the melt reaction coefficient and Mcpx is the modal abundance of clinopyroxene in the DMM. Using this equation, we calculate that the average upper mantle sulfur concentration is 195±45μg/g. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-04T05:01:26.332794-05:
      DOI: 10.1002/2014GC005536
       
  • Three‐dimensional numerical simulations of crustal systems
           undergoing orogeny and subjected to surface processes
    • Authors: C. Thieulot; P. Steer, R.S. Huismans
      Pages: n/a - n/a
      Abstract: As several modeling studies indicate, the structural expression and dynamic behavior of orogenic mountain belts is dictated not only by their rheological properties or by far‐field tectonic motion, but also by the efficiency of erosion and sedimentation acting on its surface. Until recently, numerical investigations have been mainly limited to 2D studies because of the high computational cost required by 3D models. Here, we have efficiently coupled the landscape evolution model Cascade with the 3D thermo‐mechanically coupled tectonics code FANTOM. Details of the coupling algorithms between both codes are given. We present results of numerical experiments designed to study the response of viscous‐plastic crustal materials subjected to convergence and to surface processes including both erosion and sedimentation. In particular, we focus on the equilibration of both the tectonic structures and on the surface morphology of the orogen. We show that increasing the efficiency of fluvial erosion increases the frontal thrust angle, which in turn decreases the width of the orogen. In addition, the maximum summit elevation of the orogen during transient evolution is significantly higher in those models showcasing surface processes than those that do not. This illustrates the strong coupling between tectonic and surface processes. We also demonstrate that an along‐strike gradient of erosion efficiency can have a major impact upon the landscape morphology and the tectonic structure and deformation of the orogen, in both the across‐ and along‐strike directions. Overall, our results suggest that surface processes, by enhancing localization of deformation, can act as a positive forcing to topographic building. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-04T04:38:07.439385-05:
      DOI: 10.1002/2014GC005490
       
  • Surface slip and off‐fault deformation patterns in the 2013 MW 7.7
           Balochistan, Pakistan earthquake: Implications for controls on the
           distribution of near‐surface coseismic slip
    • Authors: Robert Zinke; James Hollingsworth, James F. Dolan
      Pages: n/a - n/a
      Abstract: Comparison of 398 fault offsets measured by visual analysis of WorldView high‐resolution satellite imagery with deformation maps produced by COSI‐Corr sub‐pixel image correlation of Landsat‐8 and SPOT5 imagery reveals significant complexity and distributed deformation along the 2013 Mw 7.7 Balochistan, Pakistan earthquake. Average slip along the main trace of the fault was 4.2 m, with local maximum offsets up to 11.4 m. Comparison of slip measured from offset geomorphic features, which record localized slip along the main strand of the fault, to the total displacement across the entire width of the surface deformation zone from COSI‐Corr reveals ~45 % off‐fault deformation. Whereas previous studies have shown that the structural maturity of the fault exerts a primary control on the total percentage of off‐fault surface deformation, large along‐strike variations in the percentage of strain localization observed in the 2013 rupture imply the influence of important secondary controls. One such possible secondary control is the type of near‐surface material through which the rupture propagated. We therefore compared the percentage off‐fault deformation to the type of material (bedrock, old alluvium, young alluvium) at the surface and the distance of the fault to the nearest bedrock outcrop (a proxy for sediment thickness along this hybrid strike‐slip/reverse slip fault). We find significantly more off‐fault deformation in younger and/or thicker sediments. Accounting for and predicting such off‐fault deformation patterns has important implications for the interpretation of geologic slip rates, especially for their use in probabilistic seismic hazard assessments, the behavior of near‐surface materials during coseismic deformation, and the future development of microzonation protocols for the built environment. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-04T04:37:32.943393-05:
      DOI: 10.1002/2014GC005538
       
  • The mantle transition zone beneath West Antarctica: Seismic evidence for
           hydration and thermal upwellings
    • Authors: E.L. Emry; A. A. Nyblade, J. Julià, S. Anandakrishnan, R. C. Aster, D. A. Wiens, A. D. Huerta, T. J. Wilson
      Pages: n/a - n/a
      Abstract: Although prior work suggests that a mantle plume is associated with Cenozoic rifting and volcanism in West Antarctica, the existence of a plume remains conjectural. Here, we use P‐wave receiver functions (PRFs) from the Antarctic POLENET array to estimate mantle transition zone thickness, which is sensitive to temperature perturbations, throughout previously unstudied parts of West Antarctica. We obtain over 8000 high‐quality PRFs using an iterative, time‐domain deconvolution method filtered with a Gaussian‐width of 0.5 and 1.0, corresponding to frequencies less than ∼0.24 Hz and ∼0.48 Hz, respectively. Single‐station and common conversion point stacks, migrated to depth using the AK135 velocity model, indicate that mantle transition zone thickness throughout most of West Antarctica does not differ significantly from the global average, except in two locations; one small region exhibits a vertically thinned (210±15km) transition zone beneath the Ruppert Coast of Marie Byrd Land and another laterally broader region shows slight, vertical thinning (225±25km) beneath the Bentley Subglacial Trench. We also observe the 520 discontinuity and a prominent negative peak above the mantle transition zone throughout much of West Antarctica. These results suggest that the mantle transition zone may be hotter than average in two places, possibly due to upwelling from the lower mantle, but not broadly across West Antarctica. Furthermore, we propose that the transition zone may be hydrated due to >100 million years of subduction beneath the region during the early Mesozoic. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-26T11:32:54.03111-05:0
      DOI: 10.1002/2014GC005588
       
  • Rock magnetism of tiny exsolved magnetite in plagioclase from a
           Paleoarchean granitoid in the Pilbara Craton
    • Authors: Yoichi Usui; Takazo Shibuya, Yusuke Sawaki, Tsuyoshi Komiya
      Pages: n/a - n/a
      Abstract: Granitoids are widespread in Precambrian terranes as well as the Phanerozoic orogenic belts, but they have garnered little attention in paleomagnetic studies, because granitoids often contain abundant coarse‐grained, magnetically unstable oxides. In this study, the first example of tiny, needle‐shaped, exsolved oxides in plagioclase in a Paleoarchean granitoid is reported. The magnetic properties of single plagioclase crystals with the exsolved oxide inclusions have been studied to determine their paleomagnetic recording fidelity. Demagnetization experiments and hysteresis parameters indicate that the oxide inclusions are near stoichiometric magnetite and magnetically very stable. First‐order reversal curve (FORC) diagrams reveal negligible magnetostatic interactions. Minimal interactions are also reflected by very efficient acquisition of anhysteretic remanent magnetization. Single plagioclase crystals exhibit strong magnetic remanence anisotropies, which require corrections to their paleodirectional and paleointensity data. Nonetheless, quantitative consideration of anisotropy tensors of the single plagioclase crystals indicates that the bias can be mitigated by properly averaging data from a few tens of single crystals. From the nonlinear thermoremanence acquisition of the plagioclase crystals, we estimate that the plagioclase crystals can reconstruct paleointensity up to 50 μT. Local metamorphic condition suggests that those magnetite may carry remanence of ca. 3.2 to 3.3 Ga. We suggest that exsolved magnetite in granitoids is potentially a suitable target for the study of the early history of the geomagnetic field, and prompt detailed microscopic investigations as well as paleomagnetic tests to constrain the age of remanence. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-24T04:20:44.136581-05:
      DOI: 10.1002/2014GC005508
       
  • Density, temperature, and composition of the North American lithosphere:
           New insights from a joint analysis of seismic, gravity, and mineral
           physics data. 1: Density structure of the crust and upper mantle
    • Authors: Mikhail K. Kaban; Magdala Tesauro, Walter D. Mooney, Sierd A.P.L. Cloetingh
      Pages: n/a - n/a
      Abstract: We introduce a new method to construct integrated 3D models of density, temperature and compositional variations of the crust and upper mantle based on a combined analysis of gravity, seismic and tomography data with mineral physics constraints. The new technique is applied to North America. In the first stage we remove the effect of the crust from the observed gravity field and topography, using a new crustal model (NACr2014). In the second step, the residual mantle gravity field and residual topography are inverted to obtain a 3D density model of the upper mantle. The inversion technique accounts for the notion that these fields are controlled by the same factors but in a different way, e.g. depending on depth and horizontal dimension. This enables us to locate the position of principal density anomalies in the upper mantle. Afterwards, we estimate the thermal contribution to the density structure by inverting two tomography models for temperature (NA07 and SL2013sv), assuming a laterally and vertically uniform ‘fertile' mantle composition. Both models show the cold internal part and the hot western margin of the continent, while in some Proterozoic regions (e.g., Grenville province) NA07 at a depth of 100 km is >200˚C colder than SL2013sv. After removing this effect from the total mantle anomalies, the residual “compositional” fields are obtained. Some features of the composition density distribution, which are invisible in the seismic tomography data, are detected for the first time in the upper mantle. These results serve as a basis for the second part of the study, in which we improve the thermal and compositional models by applying an iterative approach to account for the effect of composition on the thermal model. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-20T22:28:36.119605-05:
      DOI: 10.1002/2014GC005483
       
  • Cogenetic late Pleistocene rhyolite and cumulate diorites from Augustine
           Volcano revealed by SIMS 238U‐230Th dating of zircon, and
           implications for silicic magma generation by extraction from mush
    • Authors: Michelle L. Coombs; Jorge A. Vazquez
      Pages: n/a - n/a
      Abstract: Augustine Volcano, a frequently active andesitic island stratocone, erupted a late Pleistocene rhyolite pumice fall that is temporally linked through zircon geochronology to cumulate dioritic blocks brought to the surface in Augustine's 2006 eruption. Zircon from the rhyolite yield a 238U‐230Th age of ca. 25 ka for their unpolished rims, and their interiors yield a bimodal age populations at ca. 26 ka and a minority at ca. 41 ka. Zircon from dioritic blocks, ripped from Augustine's shallow magmatic plumbing system and ejected during the 2006 eruption, have interiors defining a ca. 26 ka age population that is indistinguishable from that for the rhyolite; unpolished rims on the dioritic zircon are dominantly younger (≤12 ka) indicating subsequent crystallization. Zircon from rhyolite and diorite overlap in U, Hf, Ti, and REE concentrations, though diorites also contain a second population of high‐U, high temperature grains. Andesites that brought dioritic blocks to the surface in 2006 contain zircon with young (≤9 ka) rims and a scattering of older ages, but few zircon that crystallized during the 26 ka interval. Both the Pleistocene‐age rhyolite and the 2006 dioritic inclusions plot along a whole‐rock compositional trend distinct from mid‐Holocene–present andesites and dacites, and the diorites, rhyolite, and two early Holocene dacites define linear unmixing trends often oblique to the main andesite array and consistent with melt (rhyolite) extraction from a mush (dacites), leaving behind a cumulate amphibole‐bearing residue (diorites). Rare zircon antecrysts up to ca. 300 ka from all rock types indicate that a Quaternary center has been present longer than preserved surficial deposits. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-20T04:19:07.986339-05:
      DOI: 10.1002/2014GC005589
       
  • Density, temperature, and composition of the North American lithosphere:
           New insights from a joint analysis of seismic, gravity, and mineral
           physics data. 2: Thermal and compositional model of the upper mantle
    • Authors: Magdala Tesauro; Mikhail K. Kaban, Walter D. Mooney, Sierd A.P.L. Cloetingh
      Pages: n/a - n/a
      Abstract: Temperature and compositional variations of the North American (NA) lithospheric mantle are estimated using a new inversion technique introduced in Part I [Kaban et al., 2014], which allows us to jointly interpret seismic tomography and gravity data, taking into account depletion of the lithospheric mantle beneath the cratonic regions. The technique is tested using two tomography models (NA07 and SL2013sv) and different lithospheric density models. The first density model (Model I) reproduces the typical compositionally stratified lithospheric mantle, which is consistent with xenolith samples from the central Slave craton, while the second one (Model II) is based on the direct inversion of the residual gravity and residual topography [Part I, Kaban et al., 2014]. The results obtained, both in terms of temperature and composition, are more strongly influenced by the input models derived from seismic tomography, rather than by the choice of lithospheric density Model I versus Model II. The final temperatures estimated in the Archean lithospheric root, are up to 150°C higher than in the initial thermal models obtained using a laterally and vertically uniform “fertile” compositional model and are in agreement with temperatures derived from xenolith data. Therefore, the effect of the compositional variations cannot be neglected when temperatures of the cratonic lithospheric mantle are estimated. Strong negative compositional density anomalies (92, characterize the lithospheric mantle of the northwestern part of the Superior craton and the central part of the Slave and Churchill craton, according to both tomographic models. The largest discrepancies between the results based on different tomography models are observed in the Proterozoic regions, such as the Trans Hudson Orogen (THO), Rocky Mountains and Colorado Plateau, which appear weakly depleted (>‐0.025 g/cm3corresponding to Mg # ~91) when NA07 is used, or locally characterized by high density bodies when model SL2013sv is used. The former results are in agreement with those based on the interpretation of xenolith data. The high density bodies might be interpreted as fragments of subducted slabs or of the advection of the lithospheric mantle induced from the eastward‐directed flat slab subduction. The selection of a seismic tomography model plays a significant role when estimating lithospheric density, temperature and compositional heterogeneity. The consideration of the results of more than one model gives a more complete picture of the possible compositional variations within the NA lithospheric mantle. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-20T04:00:40.171624-05:
      DOI: 10.1002/2014GC005484
       
  • Imaging methane hydrates growth dynamics in porous media using synchrotron
           X‐ray computed microtomography
    • Authors: Prasad B. Kerkar; Kristine Horvat, Keith W. Jones, Devinder Mahajan
      Pages: n/a - n/a
      Abstract: Commercial‐scale methane (CH4) extraction from natural hydrate deposits remains a challenge due to, among other factors, a poor understanding of hydrate‐host sediment interactions under low‐temperature and high‐pressure conditions that are conducive to their existence. We report the use of synchrotron X‐ray computed microtomography (CMT) to image, for the first time, time‐resolved pore‐scale methane CH4 hydrate growth from an aqueous solution containing 5wt% barium chloride (BaCl2) and pressurized CH4 hosted in glass beads, all contained in an aluminum cell with an effective volume of 3.5mL. Multiple two‐dimensional (2‐D) cross sectional images show CH4 hydrates, with 7.5 µm resolution, distributed in patches throughout the system without dependence on distance from the cell walls. The time‐resolved three‐dimensional (3‐D) images, constructed from the 2‐D slices, exhibited pore‐filling hydrate formation from dissolved CH4 gas, similar to natural CH4 hydrates (sI) in the marine environment. Furthermore, the 3‐D images show that the aqueous phase was the wetting phase of the glass beads, i.e., the host and the formed hydrate were separated by an aqueous layer. These results provide some fundamental understanding of the nucleation phenomenon of gas hydrate formation at the pore scale. Pore‐filling CH4 hydrate growth is likely to result in a reduced bulk modulus, and thus could affect seafloor stability during the reverse phenomenon, i.e, dissociation of natural hydrate deposits. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-18T09:46:56.829667-05:
      DOI: 10.1002/2014GC005373
       
  • The ability of rock physics models to infer marine in situ pore pressure
    • Authors: Matthew J. Hornbach; Michael Manga
      Pages: n/a - n/a
      Abstract: Pore fluid pressure is an important parameter defining the mechanical strength of marine sediments. Obtaining high spatial resolution in situ pore pressure measurements in marine sediments, however, is a challenge, and as a result, only a handful of in situ pore pressure measurements exist at scientific drill sites. Integrating rock physics models with standard IODP measurements provides a potentially widely applicable approach for calculating in situ pore pressure. Here, we use a rock physics approach to estimate in situ pore pressure at two Scientific Ocean Drill Sites where in situ pressure is well‐constrained: ODP Site 1173, used as reference for normal (hydrostatic) fluid pressures, and ODP Site 948, where previous studies infer high fluid pressures (λ*∼ 0.45‐0.95, where the pore pressure ratio λ* is defined as the pore pressure above hydrostatic divided by the difference between the largest principal stress and hydrostatic stress). Our analysis indicates that the rock physics method provides an accurate, low‐precision method for estimating in situ pore pressure at these drill sites, and sensitivity analysis indicates this method can detect modestly high (λ*>0.6) pore pressure at the 95% confidence level. This approach has broad applicability because it provides an inexpensive, high‐resolution (meter‐scale) method for retrospectively detecting and quantifying high pore pressure at any drill site where quality wire‐line logs and ocean drilling data exists. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-18T09:46:49.975548-05:
      DOI: 10.1002/2014GC005442
       
  • Development and evolution of detachment faulting along 50km of the
           Mid‐Atlantic Ridge near 16.5°N
    • Authors: Deborah K. Smith; Hans Schouten, Henry Dick, Joe Cann, Vincent Salters, Horst R. Marschall, Fuwu Ji, Dana Yoerger, Alessio Sanfilippo, Ross Parnell‐Turner, Camilla Palmiotto, Alexei Zheleznov, Hailong Bai, Will Junkin, Ben Urann, Spencer Dick, Margaret Sulanowska, Peter Lemmond, Scott Curry
      Pages: n/a - n/a
      Abstract: A multifaceted study of the slow‐spreading Mid‐Atlantic Ridge (MAR) at 16.5ºN provides new insights into detachment faulting and its evolution through time. The survey included regional multibeam bathymetry mapping, high‐resolution mapping using AUV Sentry, seafloor imaging using the TowCam system, and an extensive rock‐dredging program. At different times, detachment faulting was active along ∼50km of the western flank of the study area, and may have dominated spreading on that flank for the last 5 Ma. Detachment morphologies vary and include a classic corrugated massif, non‐corrugated massifs, and back‐tilted ridges marking detachment breakaways. High‐resolution Sentry data reveal one other detachment morphology; a low‐angle, irregular surface in the regional bathymetry is shown to be a finely corrugated detachment surface (corrugation wavelength of only tens of meters and relief of just a few meters). Multi‐scale corrugations are observed 2‐3km from the detachment breakaway suggesting that they formed in the brittle layer, perhaps by anastomosing faults. The thin wedge of hanging wall lavas that covers a low‐angle (6º) detachment footwall near its termination are intensely faulted and fissured; this deformation may be enhanced by the low‐angle of the emerging footwall. Active detachment faulting currently is limited to the western side of the rift valley. Nonetheless, detachment fault morphologies also are present over a large portion of the eastern flank on crust > 2 Ma indicating that within the last 5 Ma parts of the ridge axis have experienced periods of two‐sided detachment faulting. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-18T09:46:12.024754-05:
      DOI: 10.1002/2014GC005563
       
  • A Cenozoic uplift history of Mexico and its surroundings from longitudinal
           river profiles
    • Authors: Simon N. Stephenson; Gareth G. Roberts, Mark J. Hoggard, Alexander C. Whittaker
      Pages: n/a - n/a
      Abstract: Geodynamic models of mantle convection predict that Mexico and western North America share a history of dynamic support. We calculate admittance between gravity and topography, which indicates that the elastic thickness of the plate in Mexico is 11 km and in western North America it is 12 km. Admittance at wavelengths > 500 km in these regions suggests that topography is partly supported by sub‐crustal processes. These results corroborate estimates of residual topography from isostatic calculations and suggest that the amount of North American topography supported by the mantle may exceed 1 km. The Cenozoic history of magmatism, sedimentary flux, thermochronometric denudation estimates and uplifted marine terraces imply that North American lithosphere was uplifted and eroded during the last 30 Ma. We jointly invert 533 Mexican and North American longitudinal river profiles to reconstruct a continent‐scale rock uplift rate history. Uplift rate is permitted to vary in space and time. Erosional parameters are calibrated using incision rate data in southwest Mexico and the Colorado Plateau. Calculated rock uplift rates were 0.15–0.2 mm/yr between 25–10 Ma. Central Mexico experienced the highest uplift rates. Central and southern Mexico continued to uplift at 0.1 mm/yr until recent times. This uplift history is corroborated by independent constraints. We predict clastic flux to the Gulf of Mexico and compare it to independent estimates. We tentatively suggest that the loop between uplift, erosion and deposition can be closed here. Mexico's staged uplift history suggests that its dynamic support has changed during the last 30 Ma. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-17T09:30:55.873118-05:
      DOI: 10.1002/2014GC005425
       
  • Sensitivity experiments on true polar wander
    • Authors: Marianne Greff‐Lefftz; Jean Besse
      Pages: n/a - n/a
      Abstract: Using sensitivity experiments based on the position of subductions and of superplumes, we derive models for the temporal evolution of 3D mass anomalies in the mantle and compute the associated inertia perturbations and polar wander. We show that although the large length‐scale mantle dynamics during the Earth's history may have been dominated by coupled supercontinent‐superplume cycles, subductions alone are sufficient to trigger major True Polar Wander (TPW) episodes, or rotation of the whole lithosphere and mantle with respect to the earth's rotation axis. We present two examples. We speculate that the distribution of continents with respect to the equator on the Earth's surface is driven by episodic subductions during the Wilson cycle: alternating fast subduction girdles around continents and upwellings during the divergence phases, with both reduced or stopped subductions activity around continents and moderate inter‐continental subductions during the convergence phases, lead to successive equatorial or polar distributions of continents, both configurations being separated by strong episodes of TPW. Finally, using plate reconstructions and geologic maps, over the period 1100–720 Ma, the period of amalgamation and destruction of the Rodinia supercontinent, we explain with our model the observed large eastward/westward and poleward/equatorward motions of the rotation axis. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-17T07:37:03.048088-05:
      DOI: 10.1002/2014GC005504
       
  • Lifting the cover of the cauldron: Convection in hot planets
    • Authors: Yanick Ricard; Stéphane Labrosse, Fabien Dubuffet
      Pages: n/a - n/a
      Abstract: Convection models of planetary mantles do not usually include a specific treatment of near‐surface dynamics. In all situations where surface dynamics is faster than internal dynamics, the lateral transport of material at the surface forbids the construction of a topography that could balance the internal convective stresses. This is the case if intense erosion erases the topography highs and fills in the depressions or if magma is transported through the lithosphere and spreads at the surface at large distances. In these cases, the usual boundary condition of numerical simulations, that the vertical velocity cancels at the surface should be replaced by a condition where the vertical flux on top of the convective mantle equilibrates that allowed by the surface dynamics. We show that this new boundary condition leads to the direct transport of heat to the surface and changes the internal convection that evolves toward a heat‐pipe pattern. We discuss the transition between this extreme situation where heat is transported to the surface to the usual situation where heat diffuses through the lithosphere. This mechanism is much more efficient to cool a planet and might be the major cooling mechanism of young planets. Even the modest effect of material transport by erosion on Earth is not without effect on mantle convection and should affect the heat flow budget of our planet. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-17T07:34:55.511295-05:
      DOI: 10.1002/2014GC005556
       
  • Crustal structure beneath the Rif Cordillera, North Morocco, from the
           RIFSIS wide‐angle reflection seismic experiment
    • Authors: Alba Gil; Josep Gallart, Jordi Diaz, Ramon Carbonell, Montserrat Torne, Alan Levander, Mimoun Harnafi
      Pages: n/a - n/a
      Abstract: The different geodynamic models proposed since the late 90's to account for the complex evolution of the Gibraltar Arc System lack definite constraints on the crustal structure of the Rif orogen. Here we present the first well‐resolved P‐wave velocity crustal models of the Rif cordillera and its southern continuation towards the Atlas made using controlled‐source seismic data. Two 300+ km‐long wide‐angle reflection profiles crossed the Rif along NS and EW trends. The profiles recorded simultaneously 5 land explosions of 1Tn each using ~850 high frequency seismometers. The crustal structure revealed from 2D forward modeling delineates a complex, laterally‐varying crustal structure below the Rif domains. The most surprising feature, seen on both profiles, is a ~50 km deep crustal root localized beneath the External Rif. To the east, the crust thins rapidly by 20 km across the Nekkor fault, indicating that the fault is a crustal scale feature. On the NS profile the crust thins more gradually to 40 km thickness beneath Middle Atlas and 42 km beneath the Betics. These new seismic results are in overall agreement with regional trends of Bouguer gravity and are consistent with recent receiver function estimates of crustal thickness. The complex crustal structure of the Rif orogen in the Gibraltar Arc is a consequence of the Miocene collision between the Iberian and African plates. Both the abrupt change in crustal thickness at the Nekkor fault and the unexpectedly deep Rif crustal root can be attributed to interaction of the subducting Alboran slab with the North African passive margin at late Oligocene‐early Miocene times.
      PubDate: 2014-11-11T01:21:30.519946-05:
      DOI: 10.1002/2014GC005485
       
  • Changing tectonic controls on the long‐term carbon cycle from
           Mesozoic to present
    • Authors: Benjamin Mills; Stuart J. Daines, Timothy M. Lenton
      Pages: n/a - n/a
      Abstract: Tectonic drivers of degassing and weathering processes are key long‐term controls on atmospheric CO2. However, there is considerable debate over the changing relative importance of different carbon sources and sinks. Existing geochemical models have tended to rely on indirect methods to derive tectonic drivers, such as inversion of the seawater87Sr/86Sr curve to estimate uplift or continental basalt area. Here we use improving geologic data to update the representation of tectonic drivers in the COPSE biogeochemical model. The resulting model distinguishes CO2 sinks from terrestrial granite weathering, total basalt weathering and seafloor alteration. It also distinguishes CO2 sources from subduction zone metamorphism and from igneous intrusions. We reconstruct terrestrial basaltic area from data on the extent of large igneous provinces, and use their volume to estimate their contribution to degassing. We adopt a recently‐published reconstruction of subduction‐related degassing, and relate seafloor weathering to ocean crust creation rate. Revised degassing alone tends to produce unrealistically high CO2, but this is counteracted by the inclusion of seafloor alteration and global basalt weathering, producing a good overall fit to Mesozoic‐Cenozoic proxy CO2 estimates and a good fit to 87Sr/86Sr data. The model predicts that seafloor alteration and terrestrial weathering made similar contributions to CO2 removal through the Triassic and Jurassic, after which terrestrial weathering increased and seafloor weathering declined. We predict that basalts made a greater contribution to silicate weathering than granites through the Mesozoic, before the contribution of basalt weathering declined over the Cenozoic due to decreasing global basaltic area.
      PubDate: 2014-11-11T00:53:59.284964-05:
      DOI: 10.1002/2014GC005530
       
  • The Iceland Basin excursion: Age, duration and excursion field geometry
    • Authors: J.E.T. Channell
      Pages: n/a - n/a
      Abstract: The Iceland Basin geomagnetic excursion coincided with the marine isotope stage (MIS) 6/7 boundary. The age and duration of the excursion, at seven North Atlantic sites with sufficient isotope data, are estimated by matching marine isotope stage (MIS) 7a‐c to a calibrated template. Two criteria for defining the excursion, virtual geomagnetic pole (VGP) latitudes
      PubDate: 2014-11-11T00:41:01.939089-05:
      DOI: 10.1002/2014GC005564
       
  • FORCulator: A micromagnetic tool for simulating first‐order reversal
           curve diagrams
    • Authors: Richard J. Harrison; Ioan Lascu
      Pages: n/a - n/a
      Abstract: We describe a method for simulating first‐order reversal curve (FORC) diagrams of interacting single‐domain particles. Magnetostatic interactions are calculated in real space, allowing simulations to be performed for particle ensembles with arbitrary geometry. For weakly interacting uniaxial particles, the equilibrium magnetization at each field step is obtained by direct solution of the Stoner‐Wohlfarth model, assuming a quasi‐static distribution of interaction fields. For all other cases, the equilibrium magnetization is calculated using an approximate iterated solution to the Landau‐Lifshitz‐Gilbert equation. Multithreading is employed to allow multiple curves to be computed simultaneously, enabling FORC diagrams to be simulated in reasonable time using a standard desktop computer. Statistical averaging and post processing lead to simulated FORC diagrams that are comparable to their experimental counterparts. The method is applied to several geometries of relevance to rock and environmental magnetism, including densely packed random clusters and partially collapsed chains. The method forms the basis of FORCulator, a freely available software tool with graphical user interface that will enable FORC simulations to become a routine part of rock magnetic studies.
      PubDate: 2014-11-10T22:39:09.987862-05:
      DOI: 10.1002/2014GC005582
       
  • The affects of alteration and porosity on seismic velocities in oceanic
           basalts and diabases
    • Authors: R. L. Carlson
      Pages: n/a - n/a
      Abstract: Seismic velocities in the lavas that cap normal oceanic crust are affected by both crack porosity and alteration of the primary mineral phases, chiefly to clays. Porosity accounts for 75‐80% of the velocity variation in sonic log velocities in the lava sections of Holes 504B and 1256D, but the effect of alteration on the properties of the basalts has not been assessed. In this analysis, the grain velocities in basalt and diabase samples are estimated from an empirical linear relationship between grain density and the P‐wave modulus. The theoretical velocity in fresh, zero‐porosity basalt or diabase is 6.96±0.07 km/sec. Grain velocities in the diabase samples are statistically indistinguishable from the theoretical velocity, and show no variation with depth; alteration does not significantly affect the velocities in the diabase samples from Hole 504B. This result is consistent with previous analyses, which demonstrated that velocities in the dikes are controlled by crack porosity. In basalt lab samples, alteration reduces the average sample grain velocity to 6.74±0.02 km/sec; cracks at the sample scale further reduce the velocity to 5.86±0.03 km/sec, and large‐scale cracks in the lavas reduce the average in situ velocity to 5.2±0.3 km/sec. Cracks account for nearly 90% of the difference between seismic (in situ) velocities and the theoretical velocity in the unaltered solid material. Basalt grain velocities show a small, but significant systematic increase with depth; the influence of alteration decreases with depth in the lavas, reaching near zero at the base of the lavas in Holes 504B and 1256D.
      PubDate: 2014-11-08T11:26:30.580818-05:
      DOI: 10.1002/2014GC005537
       
  • A joint Monte Carlo analysis of seafloor compliance, Rayleigh wave
           dispersion, and receiver functions at ocean bottom seismic stations
           offshore New Zealand
    • Authors: Justin S. Ball; Anne F. Sheehan, Joshua C. Stachnik, Fan‐Chi Lin, John A. Collins
      Pages: n/a - n/a
      Abstract: Teleseismic body‐wave imaging techniques such as receiver function analysis can be notoriously difficult to employ on ocean‐bottom seismic data due largely to multiple reverberations within the water and low‐velocity sediments. In lieu of suppressing this coherently scattered noise in ocean‐bottom receiver functions, these site effects can be modeled in conjunction with shear velocity information from seafloor compliance and surface wave dispersion measurements to discern crustal structure. A novel technique to estimate 1D crustal shear‐velocity profiles from these data using Monte Carlo sampling is presented here. We find that seafloor compliance inversions and P‐S conversions observed in the receiver functions provide complimentary constraints on sediment velocity and thickness. Incoherent noise in receiver functions from the MOANA ocean bottom seismic experiment limit the accuracy of the practical analysis at crustal scales, but synthetic recovery tests and comparison with independent unconstrained nonlinear optimization results affirm the utility of this technique in principle.
      PubDate: 2014-11-08T11:15:56.574721-05:
      DOI: 10.1002/2014GC005412
       
  • Soil CO2 emissions as a proxy for heat and mass flow assessment,
           Taupō Volcanic Zone, New Zealand
    • Authors: Bloomberg S; Werner C, Rissmann C, Mazot A, Horton T, Gravley D, Kennedy B, Oze C.
      Pages: n/a - n/a
      Abstract: The quantification of heat and mass flow between deep reservoirs and the surface is important for understanding magmatic and hydrothermal systems. Here, we use high‐resolution measurement of carbon dioxide flux (ϕCO2) and heat flow at the surface to characterize the mass (CO2 and steam) and heat released to the atmosphere from two magma‐hydrothermal systems. Our soil gas and heat flow surveys at Rotokawa and White Island in the Taupō Volcanic Zone, New Zealand, include over 3,000 direct measurements of ϕCO2 and soil temperature and 60 carbon isotopic values on soil gases. Carbon dioxide flux was separated into background and magmatic/hydrothermal populations based on the measured values and isotopic characterization. Total CO2 emission rates (ΣCO2) of 441 ± 84 t d‐1 and 124 ± 18 t d‐1 were calculated for Rotokawa (2.9 km2) and for the crater floor at White Island (0.3 km2), respectively. The total CO2 emissions differ from previously published values by +386 t d‐1 at Rotokawa and +25 t d‐1 at White Island, demonstrating that earlier research underestimated emissions by 700% (Rotokawa) and 25% (White Island). These differences suggest that soil CO2 emissions facilitate more robust estimates of the thermal energy and mass flux in geothermal systems than traditional approaches. Combining the magmatic/hydrothermal‐sourced CO2 emission (constrained using stable isotopes) with reservoir H2O:CO2 mass ratios and the enthalpy of evaporation, the surface expression of thermal energy release for the Rotokawa hydrothermal system (226 MWt) is 10 times greater than the White Island crater floor (22.5 MWt).
      PubDate: 2014-11-05T01:46:56.453817-05:
      DOI: 10.1002/2014GC005327
       
  • Influence of late Pleistocene glaciations on the hydrogeology of the
           continental shelf offshore Massachusetts, USA
    • Authors: Jacob Siegel; Mark Person, Brandon Dugan, Denis Cohen, Daniel Lizarralde, Carl Gable
      Pages: n/a - n/a
      Abstract: Multiple late Pleistocene glaciations that extended onto the continental shelf offshore Massachusetts, USA may have emplaced as much as 100 km3 of freshwater (salinity less than 5 ppt) in continental shelf sediments. To estimate the volume and extent of offshore freshwater, we developed a three‐dimensional, variable‐density model that couples fluid flow and heat and solute transport for the continental shelf offshore Massachusetts. The stratigraphy for our model is based on high‐resolution, multi‐channel seismic data. The model incorporates the last 3 Ma of climate history by prescribing boundary conditions of sea‐level change and ice sheet extent and thickness. We incorporate new estimates of the maximum extent of a late Pleistocene ice sheet to near the shelf‐slope break. Model results indicate that this late Pleistocene ice sheet was responsible for much of the emplaced freshwater. We predict that the current freshwater distribution may reach depths of up to 500 m below sea level and up to 30 km beyond Martha's Vineyard. The freshwater distribution is strongly dependent on the three‐dimensional stratigraphy and ice‐sheet history. Our predictions improve our understanding of the distribution of offshore freshwater, a potential non‐renewable resource for coastal communities along recently glaciated margins.
      PubDate: 2014-10-30T04:12:52.645546-05:
      DOI: 10.1002/2014GC005569
       
  • The flow structure of jets from transient sources and implications for
           modeling short‐duration explosive volcanic eruptions
    • Authors: K. N. Chojnicki; A. B. Clarke, R. J. Adrian, J.C. Phillips
      Pages: n/a - n/a
      Abstract: We used laboratory experiments to examine the rise process in neutrally‐buoyant jets that resulted from an unsteady supply of momentum, a condition that defines plumes from discrete Vulcanian‐ and Strombolian‐style eruptions. We simultaneously measured the analog‐jet discharge rate (the supply rate of momentum) and the analog‐jet internal velocity distribution (a consequence of momentum transport and dilution). Then, we examined the changes in the analog‐jet velocity distribution over time to assess the impact of the supply‐rate variations on the momentum‐driven rise dynamics. We found that the analogue jet velocity distribution changes significantly and quickly as the supply rate varied, such that the whole‐field distribution at any instant differed considerably from the time‐average. We also found that entrainment varied in space and over time with instantaneous entrainment coefficient values ranging from 0 to 0.93 in an individual unsteady jet. Consequently, we conclude that supply rate variations exert first‐order control over jet dynamics, and therefore cannot be neglected in models without compromising their capability to predict large‐scale eruption behavior. These findings emphasize the fundamental differences between unsteady and steady jet dynamics, and show clearly that: (i) variations in source momentum flux directly control the dynamics of the resulting flow; and (ii) impulsive flows driven by sources of varying flux cannot reasonably be approximated by quasi‐steady flow models. New modeling approaches capable of describing the time‐dependent properties of transient volcanic eruption plumes are needed before their trajectory, dilution and stability can be reliably computed for hazards management.
      PubDate: 2014-10-30T02:35:21.635712-05:
      DOI: 10.1002/2014GC005471
       
  • Understanding a submarine eruption through time series hydrothermal plume
           sampling of dissolved and particulate constituents: West Mata,
           2008–2012
    • Authors: Tamara Baumberger; Marvin D. Lilley, Joseph A. Resing, John E. Lupton, Edward T. Baker, David A. Butterfield, Eric J. Olson, Gretchen L. Früh‐Green
      Pages: n/a - n/a
      Abstract: Four cruises between 2008 and 2012 monitored the continuing eruption of West Mata volcano in the NE Lau Basin as it produced plumes of chemically altered water above its summit. Although large enrichments in 3He, CO2, Fe, and Mn were observed in the plumes, the most notable enrichment was that of H2, which reached concentrations as high as 14843 nM. Strongly enriched H2 concentrations in the water column result from reactions between seawater or magmatic water and extremely hot rocks. In 2008, the observation of elevated H2 concentrations in the water column above West Mata pointed to vigorous ongoing eruptions at the volcano's summit. The eruption was confirmed by visual observations made by the ROV Jason 2 in 2009 and demonstrated that H2 measurements are a vital instrument to detect ongoing volcanic eruptions at the seafloor. Elevated H2 in 2010 showed that the eruption was ongoing, although at a reduced level given a maximum H2 concentration of 4410 nM. In 2012, H2 levels in the water column declined significantly, to a maximum of only 7 nM, consistent with visual observations from the Quest‐4000 ROV that found no evidence of an ongoing volcanic eruption. Methane behaved independently of other measured gases and its concentrations in the hydrothermal plume were very low. We attribute its minimal enrichments to a mixture of mantle carbon reduced to CH4 and biological CH4 from diffuse flow sites. This study demonstrates that ongoing submarine volcanic eruptions are characterized by high dissolved H2 concentrations present in the overlying water column.
      PubDate: 2014-10-30T00:42:49.816508-05:
      DOI: 10.1002/2014GC005460
       
 
 
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