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Geochemistry, Geophysics, Geosystems

Cover image for Geochemistry, Geophysics, Geosystems

September 2012

Volume 13, Issue 9

    1. You have free access to this content
      Improved determination of marine sedimentation rates using 230Thxs

      Mark D. Bourne, Alex L. Thomas, Conall Mac Niocaill and Gideon M. Henderson

      Article first published online: 29 SEP 2012 | DOI: 10.1029/2012GC004295

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      Key Points

      • Using 230-thorium-excess allows more accurate determination of sediment fluxes
      • We suggest modifications to the calculation of 230-thorium-excess
      • We present new free software, 'XSage,' that can calculate 230-thorium-excess
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      Multiproxy characterization and budgeting of terrigenous end-members at the NW African continental margin

      Janna Just, David Heslop, Tilo von Dobeneck, Torsten Bickert, Mark J. Dekkers, Thomas Frederichs, Inka Meyer and Matthias Zabel

      Article first published online: 29 SEP 2012 | DOI: 10.1029/2012GC004148

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      Key Points

      • Novel approach to find volume calibrated magnetic and geochemical properties
      • Multiproxy properties enable discrimination of fluvial and aeolian sources
      • Dust accumulation during Heinrich Stadial 1 was 80 times higher than today
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      Signatures and significance of aeolian, fluvial, bacterial and diagenetic magnetic mineral fractions in Late Quaternary marine sediments off Gambia, NW Africa

      Janna Just, Mark J. Dekkers, Tilo von Dobeneck, Annelies van Hoesel and Torsten Bickert

      Article first published online: 29 SEP 2012 | DOI: 10.1029/2012GC004146

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      Key Points

      • Quantification of bacterial magnetite and diagenesis marine sediments
      • Hematite/goethite ratio is characteristic for fluvial and aeolian end-members
      • Heinrich Stadial 1 has the highest relative abundance of the aeolian end-member
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      Rapid post-mortem maturation of diatom silica oxygen isotope values

      Justin P. Dodd, Zachary D. Sharp, Peter J. Fawcett, Adrian J. Brearley and Francis M. McCubbin

      Article first published online: 28 SEP 2012 | DOI: 10.1029/2011GC004019

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      Key Points

      • D18Odiatom values undergo significant post-mortem alteration (>7 permil)
      • D18Odiatom values are rapidly reequilibrated
      • Mature diatom d18O values approach isotopic equilibrium for quartz-water
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      The Amsterdam–St. Paul Plateau: A complex hot spot/DUPAL-flavored MORB interaction

      M. Janin, C. Hémond, M. Maia, P. Nonnotte, E. Ponzevera and K. T. M. Johnson

      Article first published online: 28 SEP 2012 | DOI: 10.1029/2012GC004165

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      Key Points

      • ASP plateau reveals three mantle sources: ASP plume, Indian DM, DUPAL input
      • ASP plume composition requires recycled pelagic sediments
      • This study supports the lower continental crust as origin for the DUPAL anomaly
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      The sources of volatile and fluid-mobile elements in the Sunda arc: A melt inclusion study from Kawah Ijen and Tambora volcanoes, Indonesia

      Nathalie Vigouroux, Paul J. Wallace, Glyn Williams-Jones, Katherine Kelley, Adam J. R. Kent and Anthony E. Williams-Jones

      Article first published online: 28 SEP 2012 | DOI: 10.1029/2012GC004192

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      Key Points

      • Kawah Ijen is a water-rich magma from the Sunda arc
      • H2O, Cl, and Sr are supplied to arc magmas from altered oceanic crust
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      Bridging onshore and offshore present-day kinematics of central and eastern Mediterranean: Implications for crustal dynamics and mantle flow

      Eugénie Pérouse, Nicolas Chamot-Rooke, Alain Rabaute, Pierre Briole, François Jouanne, Ivan Georgiev and Dimitar Dimitrov

      Article first published online: 26 SEP 2012 | DOI: 10.1029/2012GC004289

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      Key Points

      • Propagation of Anatolian Fault throughout continental Greece is not required
      • Extension in the Corinth Gulf and in the Balkans is due to slab retreat
      • Absolute velocity field is toroidal at both ends of the Hellenic subduction
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      Melt inclusions reveal geochemical cross-arc variations and diversity within magma chambers feeding the Higashi-Izu Monogenetic Volcano Field, Izu Peninsula, Japan

      A. R. L. Nichols, R. J. Wysoczanski, K. Tani, Y. Tamura, J. A. Baker and Y. Tatsumi

      Article first published online: 26 SEP 2012 | DOI: 10.1029/2012GC004222

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      Key Points

      • Contribution from fluid component to subduction zone melting varies on km scale
      • Inclusions reveal heterogeneities in melt compositions on crystal scales
      • Interstitial melts in crystal mushes follow distinct crystallization paths
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      The internal structure of an oceanic core complex: An integrated analysis of oriented borehole imagery from IODP Hole U1309D (Atlantis Massif)

      Nicola Pressling, Antony Morris, Barbara E. John and Christopher J. MacLeod

      Article first published online: 25 SEP 2012 | DOI: 10.1029/2012GC004061

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      Key Points

      • Provide insights into the structural architecture of an oceanic core complex
      • Determine the depth extent of detachment-related deformation
      • Integrate unoriented core observations with fully oriented logging data
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      Uncertainty estimation for databased bathymetry using a Bayesian network approach

      Paul A. Elmore, David H. Fabre, Raymond T. Sawyer and R. Wade Ladner

      Article first published online: 22 SEP 2012 | DOI: 10.1029/2012GC004144

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      Key Points

      • Bayes network approach used to estimate databased bathymetric uncertainty
      • Method back-populates uncertainty to databased bathymetry data that lack it
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      Controls of faulting and reaction kinetics on serpentinization and double Benioff zones

      Karthik Iyer, Lars H. Rüpke, Jason Phipps Morgan and Ingo Grevemeyer

      Article first published online: 21 SEP 2012 | DOI: 10.1029/2012GC004304

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      Key Points

      • Extent and degree of mantle serpentinization prior to subduction
      • Depths of lower plane of double Benioff zones and maximum serpentinization
      • Link between hydrothermal circulation, serpentinization and surface heat flux
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      The Pacific lithosphere-asthenosphere boundary: Seismic imaging and anisotropic constraints from SS waveforms

      Catherine A. Rychert, Nicholas Schmerr and Nicholas Harmon

      Article first published online: 21 SEP 2012 | DOI: 10.1029/2012GC004194

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      Key Points

      • New studies image Pacific LAB, but age-depth dependance/mechanism are unclear
      • Anisotropy explains apparent discrepancies in presence/absence of a strong LAB
      • Anisotropy is an important factor in imaging and defining the oceanic LAB
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      An experimental evaluation of the use of C3 δ13C plant tissue as a proxy for the paleoatmospheric δ13CO2 signature of air

      B. H. Lomax, C. A. Knight and J. A. Lake

      Article first published online: 20 SEP 2012 | DOI: 10.1029/2012GC004174

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      Key Points

      • Carbon isotope plant values show weak correlation to atmospheric CO2 isotope values
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      Major element variations in Hawaiian shield lavas: Source features and perspectives from global ocean island basalt (OIB) systematics

      Matthew G. Jackson, Dominique Weis and Shichun Huang

      Article first published online: 19 SEP 2012 | DOI: 10.1029/2012GC004268

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      Key Points

      • Major elements correlate with radiogenic isotopes in Hawaiian lavas
      • The correlations help constrain the source lithologies in the Hawaiian plume
      • The correlations in Hawaii follow, in microcosm, the larger global correlation
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      Short wavelength heterogeneity in the Galápagos plume: Evidence from compositionally diverse basalts on Isla Santiago

      S. A. Gibson, D. G. Geist, J. A. Day and C. W. Dale

      Article first published online: 19 SEP 2012 | DOI: 10.1029/2012GC004244

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      Key Points

      • Galapagos mantle plume is compositionally heterogeneous at short wavelengths
      • Compositional diversity in Santiago basalts reflects mantle heterogeneity
      • Geochemical and geophysical models suggest a lithospheric step below Galapagos
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      Carbon cycle dynamics following the end-Triassic mass extinction: Constraints from paired δ13Ccarb and δ13Corg records

      Aviv Bachan, Bas van de Schootbrugge, Jens Fiebig, Christopher A. McRoberts, Gloria Ciarapica and Jonathan L. Payne

      Article first published online: 19 SEP 2012 | DOI: 10.1029/2012GC004150

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      Key Points

      • 13C enrichment occurs above last Triassic fossils in Italian sections
      • Co-variation of d13Ccarb and d13org indicates a primary origin for enrichment
      • Enrichment reflects elevated organic carbon burial in aftermath of extinction
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      Deformation associated with the denudation of mantle-derived rocks at the Mid-Atlantic Ridge 13°–15°N: The role of magmatic injections and hydrothermal alteration

      Suzanne Picazo, Mathilde Cannat, Adélie Delacour, Javier Escartín, Stéphane Rouméjon and Sergei Silantyev

      Article first published online: 14 SEP 2012 | DOI: 10.1029/2012GC004121

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      Key Points

      • Gabbroic protolith for injections in ultramafic rocks
      • Types of deformation affecting ultramafic rocks
      • Localization of deformation in hydrous minerals
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      Tectonic and magmatic controls on hydrothermal activity in the Woodlark Basin

      T. E. Laurila, S. Petersen, C. W. Devey, E. T. Baker, N. Augustin and M. D. Hannington

      Article first published online: 13 SEP 2012 | DOI: 10.1029/2012GC004247

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      Key Points

      • Hydrothermal activity is anomalously scarce in the Woodlark Basin
      • This is due to the tectonic setting of this young ocean basin
      • Woodlark is a poor mineral resources prospect, contrary to accepted wisdom
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      Thermal-elastic stresses and the criticality of the continental crust

      C. E. Schrank, F. Fusseis, A. Karrech and K. Regenauer-Lieb

      Article first published online: 13 SEP 2012 | DOI: 10.1029/2012GC004085

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      Key Points

      • We investigate internal stresses in granite due to burial
      • Synchrotron tomography is combined with numerical heating experiments
      • Thermal-elastic stresses may render the continental crust close to criticality
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      An assessment of geochemical preparation methods prior to organic carbon concentration and carbon isotope ratio analyses of fine-grained sedimentary rocks

      Sven F. Könitzer, Melanie J. Leng, Sarah J. Davies and Michael H. Stephenson

      Article first published online: 13 SEP 2012 | DOI: 10.1029/2012GC004094

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      Key Points

      • Acid treatment of geological sample material to remove carbonate
      • Test for extraneous hydrocarbons using stable carbon isotope ratios
      • Examining drilling mud contamination using stable carbon isotope ratios
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      Experimental assessment of the purity of α-cellulose produced by variations of the Brendel method: Implications for stable isotope (δ13C, δ18O) dendroclimatology

      Tom Brookman and Thomas Whittaker

      Article first published online: 11 SEP 2012 | DOI: 10.1029/2012GC004215

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      Key Points

      • SBrendel variations dealt with extraction requirements of resinous species
      • Reaction time, reagent amount, and temperature all affect SBrendel's efficacy
      • C and O isotope ratios potentially suspect without testing cellulose purity
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      I-STAL, a model for interpretation of Mg/Ca, Sr/Ca and Ba/Ca variations in speleothems and its forward and inverse application on seasonal to millennial scales

      Heather M. Stoll, Wolfgang Müller and Manolo Prieto

      Article first published online: 11 SEP 2012 | DOI: 10.1029/2012GC004183

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      Key Points

      • We develop a forward and inverse model for speleothem Mg/Ca, Sr/Ca, and Ba/Ca
      • Dripwater saturation state and cave pCO2 strongly affect speleothem trace element
      • Published trace element records reproduced with reasonable parameters
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      A global evaluation of temperature and carbonate ion control on Mg/Ca ratios of ostracoda genus Krithe

      A. C. Elmore, S. Sosdian, Y. Rosenthal and J. D. Wright

      Article first published online: 8 SEP 2012 | DOI: 10.1029/2012GC004073

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      Key Points

      • Mg/Ca of Krithe is primarily controlled by bottom water temperature
      • Carbonate ion is a secondary control on Mg/Ca in Krithe carapaces
      • Krithe Mg/Ca is a useful paleotemperature proxy with additional constraints
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      Kinematic interpretation of the 3D shapes of metamorphic core complexes

      Laetitia Le Pourhiet, Benjamin Huet, Dave A. May, Loic Labrousse and Laurent Jolivet

      Article first published online: 7 SEP 2012 | DOI: 10.1029/2012GC004271

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      Key Points

      • 3D finite-strain within MCCs records past plate kinematics
      • Non-cylindrical MCCs mark the influence of strike-slip kinematics
      • Constriction within MCCs do not imply shortening
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      Deep sea hydrothermal plumes and their interaction with oscillatory flows

      Guangyu Xu and Daniela Di Iorio

      Article first published online: 4 SEP 2012 | DOI: 10.1029/2012GC004188

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      Key Points

      • Long-term acoustic measurement of hydrothermal plume vertical velocity
      • Entrainment of ambient ocean water is enhanced by horizontal cross flows
      • Vertical rise height of the plume is dependent on the horizontal cross flow
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      The effective elastic thickness of the continental lithosphere: Comparison between rheological and inverse approaches

      Magdala Tesauro, Pascal Audet, Mikhail K. Kaban and Roland Bürgmann, Sierd Cloetingh

      Article first published online: 1 SEP 2012 | DOI: 10.1029/2012GC004162

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      Key Points

      • Comparison of the Te of the lithosphere based on two different methods
      • The two models have equal means in about half of the continental areas
      • The two models show higher similarities in the orogens than in the cratons

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