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Geochemistry, Geophysics, Geosystems

Cover image for Geochemistry, Geophysics, Geosystems

May 2012

Volume 13, Issue 5

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      Tracking lava flow emplacement on the east rift zone of Kīlauea, Hawai‘i, with synthetic aperture radar coherence

      Hannah R. Dietterich, Michael P. Poland, David A. Schmidt, Katharine V. Cashman, David R. Sherrod and Arkin Tapia Espinosa

      Version of Record online: 1 MAY 2012 | DOI: 10.1029/2011GC004016

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      Key Points

      • Lava flows can be mapped through time with SAR coherence images
      • Observations include flow morphology, advance rate, volume, and subsidence
      • Flows stay decorrelated long after emplacement due to settling and deflation
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      Controls of bathymetric relief on hydrothermal fluid flow at mid-ocean ridges

      Nasser Bani-Hassan, Karthik Iyer, Lars H. Rüpke and Andrea Borgia

      Version of Record online: 2 MAY 2012 | DOI: 10.1029/2012GC004041

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      Key Points

      • Simulations show that venting occurs predominantly at bathymetric highs
      • Plume deviation depends on surface slope and heat source depth
      • Bathymetric relief needed for on-axis venting at fast spreading ridges
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      Tracking the magmatic evolution of island arc volcanism: Insights from a high-precision Pb isotope record of Montserrat, Lesser Antilles

      M. Cassidy, R. N. Taylor, M. R. Palmer, R. J. Cooper, C. Stenlake and J. Trofimovs

      Version of Record online: 2 MAY 2012 | DOI: 10.1029/2012GC004064

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      Key Points

      • We detail a complete isotopic stratigraphy for Montserrat island over 2 Myr
      • We identify two different isotope trends from volcanoes active at the same time
      • Our theory suggests how tectonics can influence the chemistry of arc magmas
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      Melting and channelized magmatic flow in chemically heterogeneous, upwelling mantle

      S. M. Weatherley and R. F. Katz

      Version of Record online: 2 MAY 2012 | DOI: 10.1029/2011GC003989

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      Key Points

      • Channelized magmatic flow may be a consequence of mantle heterogeneity
      • Conservation of energy is an important ingredient of models of magma dynamics
      • Thermal diffusion and reactive flow power melting within channels
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      Quantification of mineral behavior in four dimensions: Grain boundary and substructure dynamics in salt

      V. E. Borthwick, S. Schmidt, S. Piazolo and C. Gundlach

      Version of Record online: 3 MAY 2012 | DOI: 10.1029/2012GC004057

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      Key Points

      • The 3DXRD technique is applicable for crystalline geological materials
      • Complicated microstructures can be resolved quantitatively
      • Thermal grooving in 2D experiments results in retardation of boundary movement
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      40Ar/39Ar ages for deep (∼3.3 km) samples from the Hawaii Scientific Drilling Project, Mauna Kea volcano, Hawaii

      Fred Jourdan, Warren D. Sharp and Paul R. Renne

      Version of Record online: 3 MAY 2012 | DOI: 10.1029/2011GC004017

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      Key Points

      • We measured the 40Ar/39Ar ages on lavas from the deepest section of the HSDP-2
      • We obtained a combined age of 681+/-120 ka at ~3.3 km depth
      • 40Ar/39Ar data show an accumulation rate 8.4 +/- 2.6 m/ka along the HSDP-2 core
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      Multiagent simulation of evolutive plate tectonics applied to the thermal evolution of the Earth

      M. Combes, C. Grigné, L. Husson, C. P. Conrad, S. Le Yaouanq, M. Parenthoën, C. Tisseau and J. Tisseau

      Version of Record online: 4 MAY 2012 | DOI: 10.1029/2011GC004014

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      Key Points

      • Tectonic processes dictate the thermal evolution of the Earth
      • Multiagent modeling allows for the description of poorly understood phenomena
      • Explicit tectonic laws can be investigated on the long term in a virtual lab
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      High resolution optically stimulated luminescence dating of a sediment core from the southwestern Sea of Okhotsk

      S. Sugisaki, J. P. Buylaert, A. S. Murray, N. Harada, K. Kimoto, Y. Okazaki, T. Sakamoto, K. Iijima, S. Tsukamoto, H. Miura and Y. Nogi

      Version of Record online: 5 MAY 2012 | DOI: 10.1029/2011GC004029

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      Key Points

      • Quartz fine grain OSL dating with marine sediments core
      • Testing most reliable water content model for OSL ages
      • Results show sedimentation rate difference before, during and after deglaciation
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      Effects of sampling and mineral separation on accuracy of detrital zircon studies

      Jiří Sláma and Jan Košler

      Version of Record online: 11 MAY 2012 | DOI: 10.1029/2012GC004106

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      Key Points

      • Effect of sampling and mineral separation on accuracy of detrital zircon studies
      • Limitations for routine sedimentary provenance analysis based on zircon dating
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      Magnetic and seismic reflection study of Lake Cheko, a possible impact crater for the 1908 Tunguska Event

      L. Gasperini, L. Cocchi, C. Stanghellini, G. Stanghellini, F. Del Bianco, M. Serrazanetti and C. Carmisciano

      Version of Record online: 12 MAY 2012 | DOI: 10.1029/2012GC004054

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      Key Points

      • This paper contributes to solving a problem lasting for almost one century
      • Lake Cheko is an impact crater for the Tunguska Event
      • The impactor is buried below 10 m of sediments at the lake center
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      Factors controlling the mode of rift interaction in brittle-ductile coupled systems: A 3D numerical study

      Vaneeda Allken, Ritske S. Huismans and Cedric Thieulot

      Version of Record online: 12 MAY 2012 | DOI: 10.1029/2012GC004077

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      Key Points

      • Three main modes: connecting, overlapping nonconnecting and distributed pure shear
      • Three factors controlling mode selection: viscosity, offset and strain weakening
      • Trade-off effect between offset, strength of coupling and strain weakening
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      A detailed paleomagnetic record between 2.1 and 2.75 Ma at IODP Site U1314 in the North Atlantic: Geomagnetic excursions and the Gauss-Matuyama transition

      Masao Ohno, Tatsuya Hayashi, Fumiki Komatsu, Fumi Murakami, Meng Zhao, Yohan Guyodo, Gary Acton, Helen F. Evans and Toshiya Kanamatsu

      Version of Record online: 12 MAY 2012 | DOI: 10.1029/2012GC004080

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      Key Points

      • Paleomagnetic record between 2.1 and 2.75 Ma in the North Atlantic
      • Geomagnetic excursions in the Matuyama and the Gauss Chron
      • Gauss-Matuyama polarity transition falls within Marine Isotope Stage 103
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      Fractal analysis and thermal-elastic modeling of a subvolcanic magmatic breccia: The role of post-fragmentation partial melting and thermal fracture in clast size distributions

      Samuel G. Roy, Scott E. Johnson, Peter O. Koons and Zhihe Jin

      Version of Record online: 12 MAY 2012 | DOI: 10.1029/2011GC004018

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      Key Points

      • Volcanic eruption can lead to a high degree of wall rock fragmentation
      • Magma introduced after fragmentation can cause partial melt of clasts
      • Postfragmentation heating can cause thermal fracture of rigid clasts
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      Integrated geophysical and hydrothermal models of flank degassing and fluid flow at Masaya volcano, Nicaragua

      S. C. P. Pearson, K. Kiyosugi, H. L. Lehto, J. A. Saballos, C. B. Connor and W. E. Sanford

      Version of Record online: 15 MAY 2012 | DOI: 10.1029/2012GC004117

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      Key Points

      • Geophysics combined with modeling is a powerful tool to map shallow subsurface
      • Groundwater convection on a volcano can explain diffuse degassing distribution
      • Near-surface structure is a major control on surface fluid flux and temperature
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      Lava accretion system around mid-ocean ridges: Volcanic stratigraphy in the Wadi Fizh area, northern Oman ophiolite

      Yuki Kusano, Yoshiko Adachi, Sumio Miyashita and Susumu Umino

      Version of Record online: 16 MAY 2012 | DOI: 10.1029/2011GC004006

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      Key Points

      • The first thorough description of the whole V1 stratigraphy of Oman
      • Temporal and special variations of the V1 show accretion process around MOR
      • Broad bulk-rock compositions of basalts are due to the segment end effect
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      Estimation of significance levels and confidence intervals for first-order reversal curve distributions

      David Heslop and Andrew P. Roberts

      Version of Record online: 18 MAY 2012 | DOI: 10.1029/2012GC004115

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      Key Points

      • FORC processing algorithms are extended to include error analysis
      • Significance levels can be mapped for FORC distributions
      • Confidence intervals can be estimated for profiles through FORC distributions
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      Seismic evidence of tectonic control on the depth of water influx into incoming oceanic plates at subduction trenches

      M. Lefeldt, C. R. Ranero and I. Grevemeyer

      Version of Record online: 18 MAY 2012 | DOI: 10.1029/2012GC004043

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      Key Points

      • Depth of water penetration into the mantle seems controlled by bending stresses
      • Bending-related normal faults permit percolation on a monthly basis
      • Large magnitude, deeper earthquakes have no or little effect on water influx
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      The low-temperature magnetic signature of Fe-rich serpentine in CM2 chondrites: Comparison with terrestrial cronstedtite and evolution with the degree of alteration

      Agnès Elmaleh, Serena Chiara Tarantino, Michele Zema, Bertrand Devouard and Michel Fialin

      Version of Record online: 19 MAY 2012 | DOI: 10.1029/2011GC003964

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      Key Points

      • Evidence for glassy magnetic behavior in the Fe-rich serpentine cronstedtite
      • Comparison between the magnetic signatures of cronstedtite and CM2 chondrites
      • Evolution of the low-T magnetic properties of CM2 chondrites with alteration
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      Ferromagnetic resonance characterization of greigite (Fe3S4), monoclinic pyrrhotite (Fe7S8), and non-interacting titanomagnetite (Fe3-xTixO4)

      Liao Chang, Michael Winklhofer, Andrew P. Roberts, Mark J. Dekkers, Chorng-Shern Horng, Lei Hu and Qianwang Chen

      Version of Record online: 19 MAY 2012 | DOI: 10.1029/2012GC004063

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      Key Points

      • The FMR spectra of a range of magnetic minerals were measured and modeled
      • There are large overlaps in FMR signatures of different magnetic minerals
      • Intact magnetosomes are a unique system with distinct FMR signatures
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      Downward continued multichannel seismic refraction analysis of Atlantis Massif oceanic core complex, 30°N, Mid-Atlantic Ridge

      A. S. Henig, D. K. Blackman, A. J. Harding, J.-P. Canales and G. M. Kent

      Version of Record online: 19 MAY 2012 | DOI: 10.1029/2012GC004059

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      Key Points

      • Atlantis Massif consists of laterally and vertically heterogeneous lithosphere
      • We interpret Atlantis Massif to have a dominantly gabbroic core
      • A propagating magma source and SE dipping fault cause the observed structure
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      Coexistence of three calcium carbonate polymorphs in the shell of the Antarctic clam Laternula elliptica

      Gernot Nehrke, Harald Poigner, Dorothee Wilhelms-Dick, Thomas Brey and Doris Abele

      Version of Record online: 24 MAY 2012 | DOI: 10.1029/2011GC003996

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      Key Points

      • Calcium carbonate polymorphs in Laternula elliptica
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      Constraining the Jurassic extent of Greater India: Tectonic evolution of the West Australian margin

      Ana D. Gibbons, Udo Barckhausen, Paul van den Bogaard, Kaj Hoernle, Reinhard Werner, Joanne M. Whittaker and R. Dietmar Müller

      Version of Record online: 25 MAY 2012 | DOI: 10.1029/2011GC003919

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      Key Points

      • To constrain the extent of Greater India using evidence offshore West Australia
      • To develop a model that incorporates the new Jurassic data off NW Australia
      • To link the Jurassic and Cretaceous spreading corridors of NW Australia
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      Sulfur isotopic compositions of fumarolic and plume gases at Mount Etna (Italy) and inferences on their magmatic source

      M. Liotta, A. Rizzo, A. Paonita, A. Caracausi and M. Martelli

      Version of Record online: 30 MAY 2012 | DOI: 10.1029/2012GC004118

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      Key Points

      • Sulfur magmatic signature at Etna is estimated as d34S=1(+/-)1.5 per mil
      • Magma degassing is able to explain a lower d34S in gases with respect to melt
      • Redox conditions of NNO >/= 1 must exist in the shallow plumbing system
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      Volume reconstruction of point cloud data sets derived from computational geodynamic simulations

      D. A. May

      Version of Record online: 31 MAY 2012 | DOI: 10.1029/2012GC004170

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      Key Points

      • We demonstrate a visualization technique for particle based geodynamic models
      • The approach utilizes a new Approximate Voronoi Diagram (AVD) algorithm
      • The new AVD approach is efficient, low memory and can be used in parallel
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      Groundwater pressure changes in Central Japan induced by the 2011 off the Pacific coast of Tohoku Earthquake

      Masakazu Niwa, Ryuji Takeuchi, Hironori Onoe, Koji Tsuyuguchi, Koichi Asamori, Koji Umeda and Kozo Sugihara

      Version of Record online: 31 MAY 2012 | DOI: 10.1029/2012GC004052

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      Key Points

      • We report distinct groundwater responses due to the 2011 Tohoku earthquake
      • The most responses are explained by the earthquake-induced dilation
      • Shaft excavations and unclogging in the faults affect the minor unique responses
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      Hydrothermal activity in the Northwest Lau Backarc Basin: Evidence from water column measurements

      J. E. Lupton, R. J. Arculus, J. Resing, G. J. Massoth, R. R. Greene, L. J. Evans and N. Buck

      Version of Record online: 31 MAY 2012 | DOI: 10.1029/2011GC003891

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      Key Points

      • This is the first report of hydrothermal activity in the NW Lau Backarc Basin
      • The region is unique in having a hotspot or OIB influence
      • It is likely that the hydrothermal systems are different from normal MOR systems
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      Multiple expressions of plume-ridge interaction in the Galápagos: Volcanic lineaments and ridge jumps

      E. Mittelstaedt, S. Soule, K. Harpp, D. Fornari, C. McKee, M. Tivey, D. Geist, M. D. Kurz, C. Sinton and C. Mello

      Version of Record online: 31 MAY 2012 | DOI: 10.1029/2012GC004093

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      Key Points

      • Ninety-four percent of volcanism near the GSC occurs on the plate overlying the plume
      • Transform perturbed stresses may control volcano locations on the Nazca Plate
      • Ridge jumps likely initiated a two-stage formation of the Galapagos Transform
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      P wave anisotropic tomography of the Nankai subduction zone in Southwest Japan

      Jian Wang and Dapeng Zhao

      Version of Record online: 31 MAY 2012 | DOI: 10.1029/2012GC004081

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      Key Points

      • The PHS slab exhibits considerable lateral variations
      • The PHS slab shows trench-parallel anisotropy in Kyushu
      • It is possible that a relation exists between slab anisotropy and seismicity
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      Towards the robust selection of Thellier-type paleointensity data: The influence of experimental noise

      Greig A. Paterson, Andrew J. Biggin, Yuhji Yamamoto and Yongxin Pan

      Version of Record online: 2 JUN 2012 | DOI: 10.1029/2012GC004046

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      Key Points

      • The effects of experimental noise on paleointensity data are investigated
      • Limits on our ability to detect non-ideal behavior are defined
      • We highlight parameters sensitive to noise and recommend a minimum fraction

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