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Geophysical Research Letters     Full-text available via subscription   (Followers: 112, SJR: 3.323, h-index: 185)
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Paleoceanography     Full-text available via subscription   (Followers: 5, SJR: 3.067, h-index: 100)
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Water Resources Research     Full-text available via subscription   (Followers: 80, SJR: 2.661, h-index: 144)
Journal Cover Geochemistry, Geophysics, Geosystems
  [SJR: 2.439]   [H-I: 91]   [26 followers]  Follow
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   ISSN (Online) 1525-2027
   Published by AGU Homepage  [17 journals]
  • Normal faulting and mass movement during ridge subduction inferred from
           porosity transition and zeolitization in the Costa Rica subduction zone
    • Authors: Mari Hamahashi; Elizabeth Screaton, Wataru Tanikawa, Yoshitaka Hashimoto, Kylara Martin, Saneatsu Saito, Gaku Kimura
      Abstract: Subduction of the buoyant Cocos Ridge offshore the Osa Peninsula, Costa Rica substantially affects the upper plate structure through a variety of processes, including outer forearc uplift, erosion, and focused fluid flow. To investigate the nature of a major seismic reflector (MSR) developed between slope sediments (late Pliocene∼late Pleistocene silty clay) and underlying higher velocity upper plate materials (late Pliocene∼early Pleistocene clayey siltstone), we infer possible mechanisms of sediment removal by examining the consolidation state, microstructure, and zeolite assemblages of sediments recovered from Integrated Ocean Drilling Program Expedition 344 Site U1380. Formation of Ca-type zeolites laumontite and heulandite, inferred to form in the presence of Ca-rich fluids, has caused porosity reduction. We adjust measured porosity values for these pore-filling zeolites and evaluated the new porosity profile to estimate how much material was removed at the MSR. Based on the composite porosity-depth curve, we infer the past burial depth of the sediments directly below the MSR. The corrected and uncorrected porosity-depth curves yield values of 800±70 m and 900±70 m, respectively. We argue that deposition and removal of this entire estimated thickness in 0.49 m.y. would require unrealistically large sedimentation rates and suggest that normal faulting at the MSR must contribute. The porosity offset could be explained with maximum 250±70 m of normal fault throw, or 350±70 m if the porosity were not corrected. The porosity correction significantly reduces the amount of sediment removal needed for the combination of mass movement and normal faulting that characterize the slope in this margin.
      PubDate: 2017-06-16T11:35:35.549751-05:
      DOI: 10.1002/2016GC006577
  • Assessing marine gas emission activity and contribution to the atmospheric
           methane inventory: A multidisciplinary approach from the Dutch Dogger Bank
           seep area (North Sea)
    • Authors: M. Römer; S. Wenau, S. Mau, M. Veloso, J. Greinert, M. Schlüter, G. Bohrmann
      Abstract: We present a comprehensive study showing new results from a shallow gas seep area in ∼40 m water depth located in the North Sea, Netherlands sector B13 that we call ‘Dutch Dogger Bank seep area'. It has been postulated that methane presumably originating from a gas reservoir in ∼600 m depth below the seafloor is naturally leaking to the seafloor. Our ship-based subbottom echosounder data indicate that the migrating gas is trapped in numerous gas pockets in the shallow sediments. The gas pockets are located at the boundary between the top of the Late Pliocene section and overlying fine grained sediments, which were deposited during the early Holocene marine transgression after the last glaciation. We mapped gas emissions during three R/V Heincke cruises in 2014, 2015, and 2016 and repeatedly observed up to 850 flares in the study area. Most of them (∼80%) were concentrated at five flare clusters. Our repeated analysis revealed spatial similarities of seep clusters, but also heterogeneities in emission intensities. A first calculation of the methane released from these clusters into the water column revealed a flow rate of 277 L/min (SD=140), with two clusters emitting 132 and 142 L/min representing the most significant seepage sites. Above these two flare clusters, elevated methane concentrations were recorded in atmospheric measurements. Our results illustrate the effective transport of methane via gas bubbles through a ∼40 m water column, and furthermore provide an estimate of the emission rate needed to allow for a contribution to the atmospheric methane concentration.
      PubDate: 2017-06-16T05:45:20.95936-05:0
      DOI: 10.1002/2017GC006995
  • Regional-scale development of opening-mode calcite veins due to silica
    • Authors: John N. Hooker; Jennifer M. Huggett, Joe Cartwright, Mohammad Ali Hussein
      Abstract: The formation and distribution of natural fractures in Cretaceous–Paleogene strata in Jordan are strongly tied to diagenetic processes, which in turn reflect the lithology of the host material. Observations collected from subsurface cores show that widespread fracturing began before compaction of the host sediment was complete, based on ptygmatic folding of one set of mineral-filled fractures (veins). Non-folded veins are preferentially developed within heavily cemented layers. Calcium carbonate is the greatest volumetric component of the host sediment, and most fractures are at least partially filled by calcite. Dolomite- and silica-bearing fractures are present in dolomitized and silicified host beds, respectively. Horizontal veins are filled by cone-in-cone calcite or, rarely, silica or dolomite. The stratigraphic arrangement and degree of compaction around ptygmatically folded calcite veins and chert nodules suggest that silica diagenesis was an important driver of early fractures. Nevertheless, those fractures were filled with carbonate cements as they opened, based on crack-seal texture of the vein fill. The volume loss associated with silica diagenesis created fracture porosity, which was filled coevally by carbonate cements. The distribution of later veins reflects embrittlement of host layers by cementation and is consistent with crustal deformation as the primary fracture driver.
      PubDate: 2017-06-15T18:05:45.773205-05:
      DOI: 10.1002/2017GC006888
  • The global systematics of primitive arc melts
    • Authors: M.W. Schmidt; O. Jagoutz
      Abstract: We extracted all volcanic arc rock analyses calculated to be in equilibrium with mantle olivine from the global georoc database. This results in 938 primitive melt compositions from 30 arcs. Based on geochemical criteria six principal types of primitive arc melts can be distinguished: calc-alkaline basalts and andesites, tholeiitic basalts, highly depleted tholeiitic andesites, shoshonites and low-Si basalts. Their major element systematics indicates that last mantle equilibration occurred mostly at 1.0-2.5 GPa, 1220-1350°C for tholeiitic and calc-alkaline basalts, at 0.5-1.2 GPa and ∼1200°C for depleted tholeiitic andesites, and at 0.7-1.2 GPa, 1050-1150°C for calc-alkaline andesites. Quantitative treatment of major and trace elements suggests that the different melt types can be explained by a combination of variable mantle wedge preconditioning (degree of depletion prior to slab component addition, metasomatism in the lithosphere), variation in the amount and nature of the slab component added, and - for primitive calc-alkaline andesites - reactive fractionation in the lithospheric top of the mantle wedge.The different slab components are best characterized by high Na2O, TiO2, Zr and Th for slab melts; high K2O/Na2O and more pronounced Nb, Sr, and Pb anomalies for fluids; and high K2O at high K2O/Na2O for supercritical liquids. A slab component that is dominantly a slab melt is common in continental but rare in intra-oceanic arcs, consistent with comparatively cooler slabs in intra-oceanic subduction zones. A majority of the arcs has more than one melt type, testifying for heterogeneity in the mantle wedge and added slab component.
      PubDate: 2017-06-15T18:00:38.593099-05:
      DOI: 10.1002/2016GC006699
  • Rates of mantle cooling and exhumation during rifting constrained by
           REE-in-pyroxene speedometry
    • Authors: A. Smye; S. Seman, M. Hudak, K. Crispin
      Abstract: Ocean basins are formed when continents are broken apart. Adiabatic melt generation that is driven by rifting of continental lithosphere is strongly dependent on the rate of extension. Slow extension results in conductive heat loss from the upwelling mantle, whereas cooling is limited during fast extension and can result in the geotherm intersecting the peridotite solidus. However, there are few direct constraints on the rates of mantle upwelling during extension of continental lithosphere. Here, we use diffusion modelling of subsolidus REE re-equilibration between orthopyroxene and clinopyroxene to show that the Lanzo peridotite massif —lithospheric mantle exhumed during opening of the Ligurian Tethys—cooled at rates between 5 and 25°C/Myr across the spinel-to-plagioclase peridotite facies transition. We show that these rates are sufficiently slow to suppress significant adiabatic melt generation, providing an explanation for the magma-poor nature of the Alpine Tethys margin.
      PubDate: 2017-06-15T17:20:44.011185-05:
      DOI: 10.1002/2017GC006957
  • Flexural isostasy of the carbonate platform in North central Florida
    • Authors: H. B. Woo; M. Panning, Peter N. Adams, A. Dutton
      Abstract: Deformed marine terraces can be used to explore a region's uplift history. Trail Ridge is a marine terrace in north Florida that is nearly 80 meters above modern sea level and contains Quaternary marine fossils, a fact that is inconsistent with estimates of paleo-sea level history since the early Pleistocene. This implies that the terrace has experienced uplift since its formation, as well as non-uniform deformation recorded by the warping of its previously horizontal state. The Florida carbonate platform, located on the passive margin of eastern North America, is a setting where non-tectonic influences (e.g. isostatic adjustment, dynamic topography) can be examined. We present a single-transect, numerical model of vertical displacement, derived from elastic flexure, to assess the influence of karst-driven isostatic uplift on present day topography of Trail Ridge in north Florida. Flexural modeling predicts elevations in central Florida not observed today, most likely because surface erosion and karst cavity collapse have obliterated this high topography. Older subsurface stratigraphic units, however, display the arched profile predicted from flexural modeling. Mass loss, calculated by differencing modeled topography and observed topography, was found to be 6.75 × 1012 kg, since emplacement of Trail Ridge. Uplift rates, assuming karst-driven flexural isostasy alone, using previously estimated ages of Trail Ridge of 0.125, 1.4, 3, or 3.5 Ma were found to be 0.535, 0.048, 0.022, and 0.019 mm/yr, respectively. A more likely explanation of uplift includes contributions from dynamic topography and glacial isostatic adjustment which should be further explored with more advanced geophysical modeling.
      PubDate: 2017-06-15T17:20:39.694771-05:
      DOI: 10.1002/2017GC006934
  • Human-induced seismicity and large-scale hydrocarbon production in the USA
           and Canada
    • Authors: Mirko van der Baan; Frank J. Calixto
      Abstract: We compare current and historic seismicity rates in six States in the USA and three Provinces in Canada to past and present hydrocarbon production. All States/Provinces are major hydrocarbon producers. Our analyses span three to five decades depending on data availability. Total hydrocarbon production has significantly increased in the past few years in these regions. Increased production in most areas is due to large-scale hydraulic fracturing and thus underground fluid injection. Furthermore, increased hydrocarbon production generally leads to increased water production, which must be treated, recycled or disposed of underground. Increased fluid injection enhances the likelihood of fault reactivation, which may affect current seismicity rates.We find that increased seismicity in Oklahoma, likely due to salt-water disposal, has an 85% correlation with oil production. Yet, the other areas do not display State/Province-wide correlations between increased seismicity and production, despite 8-16 fold increases in production in some States. However in various cases seismicity has locally increased.Multiple factors play an important role in determining the likelihood of anthropogenic activities influencing earthquake rates, including (i) the near-surface tectonic background rate, (ii) the existence of critically stressed and favorably oriented faults, which must be hydraulically connected to injection wells, (iii) the orientation and magnitudes of the in situ stress field, combined with (iv) the injection volumes and implemented depletion strategies. A comparison with the seismic hazard maps for the USA and Canada shows that induced seismicity is less likely in areas with a lower hazard. The opposite however is not necessarily true.
      PubDate: 2017-06-09T11:00:46.374601-05:
      DOI: 10.1002/2017GC006915
  • Observed correlation between the depth to base and top of gas hydrate
           occurrence from review of global drilling data
    • Authors: M. Riedel; T.S. Collett
      Abstract: A global inventory of data from gas hydrate drilling expeditions is used to develop relationships between the base of structure I gas hydrate stability, top of gas hydrate occurrence, sulfate-methane transition depth, pressure (water depth), and geothermal gradients. The motivation of this study is to provide first-order estimates of the top of gas hydrate occurrence and associated thickness of the gas hydrate occurrence zone for climate-change scenarios, global carbon budget analyses, or gas hydrate resource assessments. Results from publically available drilling campaigns (21 expeditions, 52 drill sites) off Cascadia, Blake Ridge, India, Korea, South China Sea, Japan, Chile, Peru, Costa Rica, Gulf of Mexico, and Borneo reveal a first-order linear relationship between the depth to the top and base of gas hydrate occurrence. The reason for these nearly linear relationships is believed to be the strong pressure- and temperature dependence of methane solubility in the absence of large difference in thermal gradients between the various sites assessed. In addition, a statistically robust relationship was defined between the thickness of the gas hydrate occurrence zone and the base of gas hydrate stability (in meters below seafloor). The relationship developed is able to predict the depth of the top of gas hydrate occurrence zone using observed depths of the base of gas hydrate stability within less than 50 meters at most locations examined in this study. No clear correlation of the depth to the top and base of gas hydrate occurrences with geothermal gradient and sulfate-methane transition depth were identified.
      PubDate: 2017-06-09T11:00:44.952881-05:
      DOI: 10.1002/2017GC006805
  • Block motion changes in Japan triggered by the 2011 Great Tohoku
    • Authors: Brendan J. Meade; John P. Loveless
      Abstract: Plate motions are governed by equilibrium between basal and edge forces. Great earthquakes may induce differential static stress changes across tectonic plates, enabling a new equilibrium state. Here we consider the torque balance for idealized circular plates and find a simple scalar relationship for changes in relative plate speed as a function of its size, upper mantle viscosity, and coseismic stress changes. Applied to Japan, the 2011 MW = 9.0 Tohoku earthquake generated coseismic stresses of 102 – 105 Pa that could have induced changes in motion of small (radius ∼ 100 km) crustal blocks within Honshu. Analysis of time-dependent GPS velocities, with corrections for earthquake cycle effects, reveals that plate speeds may have changed by up to ∼ 3 mm/yr between ∼ 3.75-year epochs bracketing this earthquake, consistent with an upper mantle viscosity of ∼ 5 × 1018 Pa·s, suggesting that great earthquakes may modulate motions of proximal crustal blocks at frequencies as high as 10−8 Hz.
      PubDate: 2017-06-09T11:00:43.463414-05:
      DOI: 10.1002/2017GC006983
  • The behaviour of iron and zinc stable isotopes accompanying the subduction
           of mafic oceanic crust: A case study from Western Alpine Ophiolites
    • Authors: Edward C. Inglis; Baptiste Debret, Kevin W. Burton, Marc-Alban Millet, Marie-Laure Pons, Christopher W. Dale, Pierre Bouilhol, Matthew Cooper, Geoffrey M. Nowell, Alex McCoy-West, Helen M. Williams
      Abstract: Arc lavas display elevated Fe3+/ΣFe ratios relative to MORB. One mechanism to explain this is the mobilization and transfer of oxidised or oxidising components from the subducting slab to the mantle wedge. Here we use iron and zinc isotopes, which are fractionated upon complexation by sulfide, chloride and carbonate ligands, to remark on the chemistry and oxidation state of fluids released during prograde metamorphism of subducted oceanic crust. We present data for metagabbros and metabasalts from the Chenaillet massif, Queyras complex and the Zermatt-Saas ophiolite (Western European Alps), which have been metamorphosed at typical subduction zone P-T conditions and preserve their prograde metamorphic history. There is no systematic, detectable fractionation of either Fe or Zn isotopes across metamorphic facies, rather the isotope composition of the eclogites overlaps with published data for MORB. The lack of resolvable Fe isotope fractionation with increasing prograde metamorphism likely reflects the mass balance of the system, and in this scenario Fe mobility is not traceable with Fe isotopes. Given that Zn isotopes are fractionated by S- and C-bearing fluids, this suggests that relatively small amounts of Zn are mobilised from the mafic lithologies in within these types of dehydration fluids. Conversely, metagabbros from the Queyras that are in close proximity to metasediments display a significant Fe isotope fractionation. The covariation of δ56Fe of these samples with selected fluid mobile elements suggests the infiltration of sediment derived fluids with an isotopically light signature during subduction.
      PubDate: 2017-06-09T11:00:35.955397-05:
      DOI: 10.1002/2016GC006735
  • The role of mud volcanism and deep-seated dewatering processes in the
           Nankai Trough accretionary prism and Kumano Basin, Japan
    • Authors: Walter Menapace; David Völker, Norbert Kaul, Michael D. Tryon, Achim J. Kopf
      Abstract: Circulation of water at moderate depths in subduction zones is dominantly driven by clay mineral dehydration over distinct pressure and temperature gradients. The signature of these dehydration reactions is found in mud volcano pore waters, however, it is largely unknown, how much of the deep-seated fluids are emitted at mud volcanoes. To unravel this relation for the region off the Kii Peninsula, Japan, we calculated the water volume that is subducted in the Nankai Trough using input data from IODP holes C0011 and C0012 and the correspondent water volume released from the subducted plate under the Kumano Basin, in an area where 13 mud volcanoes are located. According to our model, water released at depth in the mud volcano area is derived almost entirely from basaltic saponite and sedimentary smectite transformation (up to 96%). Nonetheless, the mud volcanoes themselves expel ≪1% of the total volume. To test the contribution of the accreted strata and the Kumano Basin fill to the water budget, we run a second model. Water loss due to compaction of sediments and smectite-illite transition below the basin floor have been calculated. The results were compared with salinity measurements on background cores scattered in the study area to extrapolate the volume of water loss at depth. The comparison of the two methods yielded similar results and led us to conclude that the bulk part of the deep-seated fluid re-enters the hydrosphere via the basin floor, a mechanism rarely taken into account in fluid budgets in the literature.
      PubDate: 2017-06-09T11:00:32.752309-05:
      DOI: 10.1002/2016GC006763
  • Stratigraphic Signatures of forearc basin formation mechanisms
    • Authors: Utsav Mannu; Kosuke Ueda, Sean D. Willett, Taras V. Gerya, Michael Strasser
      Abstract: Tectonic deformation of accretionary wedges is often interpreted using stratigraphic patterns observed in forearc basins. However, similar stratigraphic patterns could evolve from different deformational processes making it difficult to uniquely reconcile stratigraphic patterns and the geodynamic history of natural accretionary wedges. Therefore, it is important to test the dynamic consistency of interpreted deformation histories. One approach is to compare synthetic stratigraphy of forearc basins generated in numerical accretionary wedge models, to the stratal patterns observed in natural forearcs. We present a simple method to simulate synthetic stratigraphy in numerical accretionary wedge models, comparable to the stratigraphic patterns observed in seismic reflection data. As calibration, we use reflection seismic and borehole data for the Kumano forearc basin in Nankai. We observe that the stratigraphy in retro-forearc basins remains predominantly undisturbed and unaffected by wedge deformation. Sediment-stabilized wedge-top basins in wedges with trenchward surface slope typically form landward of an active out-of-sequence thrust, leading to a landward tilting of the basin. These stratigraphic characteristics are diagnostic of the forearc basin forming mechanism. We also infer that sedimentation in the trench can potentially influence the generation/reactivation of Megasplay Fault activity in the Nankai accretionary wedge. Activity on the Megasplay Fault helps create accommodation space landward to it that leads to the formation of Kumano forearc basin.
      PubDate: 2017-06-05T11:01:19.054413-05:
      DOI: 10.1002/2017GC006810
  • An experimental study of CO2-oil-brine-rock interaction under in situ
           reservoir conditions
    • Authors: Zhichao Yu; Keyu Liu, Li Liu, Siyu Yang, Yongzhi Yang
      Abstract: To understand the mineralogical and chemical changes in oil–bearing reservoirs (e.g. depleted oil reservoirs) during massive CO2 injection, we have carried out a core-flooding experimental study of CO2–oil–brine–rock interactions under a simulated reservoir condition of 100°C and 24 MPa. The experimental condition is based on field data from a CO2–EOR project in the southern Songliao Basin. This oil–bearing CO2–flooding experiment used the same experimental setup, reservoir conditions and workflow as the oil–free experiment reported by Yu et al. (2012). The sandstone core samples used in the experiment have similar mineralogical compositions as that used in the previous experiment. Compared with the oil–free experiment, the presence of oil appears to substantially reduce the reaction degree between the CO2 fluid and some sensitive minerals. The dissolution rates of the K–feldspar and carbonate minerals for the oil–bearing experiment are 1/5 and 1/4 of that for the oil–free experiments, respectively. For the silicate minerals represented by the K–feldspar, the presence of oil mainly delays the dissolution during the experiment, and reduces the equilibrium dissolution rate. For the carbonate minerals, the presence of oil appears to primarily affect the dissolution at the beginning of the experiments, and reduce the maximum dissolution rate attained. The core permeabilities for the oil–free and oil–bearing cases are both reduced after experiments. The reduction in permeability is probably due to the precipitation of fine siliceous mineral and clay particles released by the dissolution of the carbonate cement, which may clog some pore throats. The results provide some new insights on the fluid-rock interaction during CO2 injection in depleted oil reservoirs or during CO2–EOR.
      PubDate: 2017-06-05T10:56:32.980102-05:
      DOI: 10.1002/2017GC006858
  • Spatial and temporal uplift history of South America from calibrated
           drainage analysis
    • Authors: V. Rodríguez Tribaldos; N. J. White, G.G. Roberts, M. J. Hoggard
      Abstract: A multi-disciplinary approach is used to analyze the Cenozoic uplift history of South America. Residual depth anomalies of oceanic crust abutting this continent help to determine the pattern of present-day dynamic topography. Admittance analysis and crustal thickness measurements indicate that the elastic thickness of the Borborema and Altiplano regions is ≤ 10 km with evidence for sub-plate support at longer wavelengths. A drainage inventory of 1827 river profiles is assembled and used to investigate landscape development. Linear inverse modeling enables river profiles to be fitted as a function of the spatial and temporal history of regional uplift. Erosional parameters are calibrated using observations from the Borborema Plateau and tested against continent-wide stratigraphic and thermochronologic constraints. Our results predict that two phases of regional uplift of the Altiplano plateau occurred in Neogene times. Regional uplift of the southern Patagonian Andes also appears to have occurred in Early Miocene times. The consistency between observed and predicted histories for the Borborema, Altiplano and Patagonian plateaux implies that drainage networks record coherent signals that are amenable to simple modeling strategies. Finally, the predicted pattern of incision across the Amazon catchment constrains solid sedimentary flux at the Foz do Amazonas. Observed and calculated flux estimates match, suggesting that erosion and deposition were triggered by regional Andean uplift during Miocene times.
      PubDate: 2017-06-02T07:05:46.559832-05:
      DOI: 10.1002/2017GC006909
  • Marine redox stratification during the early Cambrian (ca. 529-509 Ma) and
    • Authors: Yuying Zhang; Zhiliang He, Shu Jiang, Bo Gao, Zhongbao Liu, Bo Han, Hu Wang
      Abstract: High resolution geochemical data from nine sections representing shelf to basinal environments in the Yangtze Platform were analyzed to reconstruct the marine redox environment during early Cambrian. Based on Fe species and Mo/TOC ratios, we have supplemented marine redox stratification during Stage 4 (late Canglangpuian-Longwangmiaoan, ∼514-509 Ma) on basis of the previously studied Stage 2-Stage 3 (Meishucunian-Qiongzhusian, ∼529-514 Ma). A new proposed marine stratified redox model indicates that the mid-depth “euxinic wedge” developed at the base of slope during ∼514-509 Ma in contrast to that the “euxinic wedge” prevailed at the shelf margin during ∼529-514 Ma, even though these mid-depth euxinic waters both occurred between the oxic surface waters and ferruginous deep waters. This marine redox stratification resulted in high production and good preservation of organic matter during early Cambrian. TOC values in euxinic waters in the middle are generally higher than in ferruginous waters due to upwelling in slope. Therefore, the lower Cambrian organic-rich shales in the Yangtze Platform are inferred to be deposited under the anoxic-ferruginous and euxinic bottom waters with moderate-strong restriction.
      PubDate: 2017-06-02T07:05:40.24199-05:0
      DOI: 10.1002/2017GC006864
  • Magnetic signature of the June 22nd, 1932 tsunami deposits (Jalisco,
           Mexican Pacific coast)
    • Authors: M.F. Bógalo; M-T. Ramírez-Herrera, A. Goguitchaichvili, D. Rey, K.J. Mohamed, M. Calvo-Rathert, N. Corona
      Abstract: Recent studies have demonstrated that rock-magnetic analysis may provide additional information to distinguish and characterize extreme marine inundation events such as tsunamis. Rock-magnetic proxies reinforce and improve the environmental evidences supplied by other methods, adding some decisive clues for the interpretation of the origin and genesis of the sedimentary deposits. Here we report rock-magnetic, XRD and SEM microscopy results obtained in the Palo Verde estuary (Colima Pacific coast, Mexico) in order to enhance the tools for identification and reconstruction of two tsunami-induced deposits. The sedimentary sequence includes two sand units, a tsunami deposit (PV1) associated with the 22 June 1932 tsunami and a deeper sandy layer (PV2) related to a possible palaeotsunami that occurred around 1300 CE. Both sandy units are topped by finer grained units.Magnetic properties exhibit a significant correlation with the stratigraphy. High susceptibility (χ) and high saturation isothermal remanence (SIRM) values typical of high concentrations of (titano)magnetite are a distinctive feature of the most recent sandy tsunamigenic unit PV1 and the overlaying soil. The lower sandy tsunamigenic unit PV2 shows significantly lower χ and SIRM values, indicating lower concentration of (titano)magnetite in this unit and the overlaying clayey-silt unit. The latter also shows a higher coercivity component associated to (titano)hematite. Magnetic grain-size differences are also observed between PV1 and PV2 suggesting differences in hydraulic conditions at the time of deposition. The bulk mineralogical composition and sediment texture of these units also supports the hypothesis of different provenances for each tsunamigenic unit as inferred from magnetic properties.
      PubDate: 2017-06-02T06:56:04.228683-05:
      DOI: 10.1002/2016GC006752
  • Faulting and off-axis submarine massive sulfide accumulation at
           slow-spreading mid-ocean ridges: A numerical modeling perspective
    • Authors: C. Andersen; S. Theissen-Krah, M. Hannington, L. Rüpke, S. Petersen
      Abstract: The potential of mining Seafloor Massive Sulfide deposits for metals such as Cu, Zn, and Au is currently debated. One key challenge is to predict where the largest deposits worth mining might form, which in turn requires understanding the pattern of sub-seafloor hydrothermal mass and energy transport. Numerical models of heat and fluid flow are applied to illustrate the important role of fault zone properties (permeability and width) in controlling mass accumulation at hydrothermal vents at slow-spreading ridges. We combine modeled mass-flow rates, vent temperatures and vent field dimensions with the known fluid chemistry at the fault-controlled Logatchev 1 hydrothermal field of the Mid-Atlantic Ridge. We predict that the 135 kilotons of SMS at this site (estimated by other studies) can have accumulated with a minimum depositional efficiency of 5% in the known duration of hydrothermal venting (58,200 year age of the deposit). In general, the most productive faults must provide an efficient fluid pathway while at the same time limit cooling due to mixing with entrained cold seawater. This balance is best met by faults that are just wide and permeable enough to control a hydrothermal plume rising through the oceanic crust. Model runs with increased basal heat input, mimicking a heat flow contribution from along-axis, lead to higher mass fluxes and vent temperatures, capable of significantly higher SMS accumulation rates. Non-steady state conditions, such as the influence of a cooling magmatic intrusion beneath the fault zone, also can temporarily increase the mass flux while sustaining high vent temperatures.
      PubDate: 2017-06-02T06:55:49.191764-05:
      DOI: 10.1002/2017GC006880
  • The Gondou hydrothermal field in the Ryukyu Arc: A huge hydrothermal
           system on the flank of a caldera volcano
    • Authors: H. Minami; Y. Ohara
      Abstract: High-resolution geophysical mapping was conducted from an autonomous underwater vehicle on the flank of Daisan-Kume Knoll in the Ryukyu Arc, southwest of Japan. 1-m resolution bathymetry identified 264 spires, 173 large mounds and 268 small mounds within a depression that is up to 1600 m wide and up to 60 m deep, at water depths between 1330 and 1470 m. Hydrothermal venting is strongly inferred from the observation of plumes in sidescan sonar imagery and positive temperature anomalies over the spires and mounds. This field, named the Gondou Field, has a giant mound G1 with a diameter of 280 m and a height of 80 m. Mound G1 has distinctive summit ridges comprised of multiple spires where acoustic plumes with temperature anomalies up to 1.12°C are observed, indicative of high-temperature venting. Other than mound G1, a number of active large mounds more than 30 m wide and spires over 10-22 m tall are common and they concentrate in the central and southern areas of the field, suggesting that these areas are the center of present hydrothermal activity. Acoustic plumes imaged by side-scan sonar at the Gondou Field are different in character from bubble plumes imaged in other hydrothermal fields in the Ryukyu Arc. The plumes are diffused and deflected as they rise through the water column and have a shape consistent with black smokers.
      PubDate: 2017-05-30T11:36:43.696855-05:
      DOI: 10.1002/2017GC006868
  • New insights into the magmatism in the northern margin of the South China
           Sea: Spatial features and volume of intraplate seamounts
    • Authors: Chaoyan Fan; Shaohong Xia, Fang Zhao, Jinlong Sun, Jinghe Cao, Huilong Xu, Kuiyuan Wan
      Abstract: The extensive intraplate seamounts are obvious features in the northern South China Sea (SCS). However, the distribution, volume, and origin of these seamounts are not well understood, which greatly hinders our understanding of magmatism in the SCS. Based on high-resolution bathymetric data and 147 seismic profiles, and combining gravity and magnetic data, we first identify 45 seamounts in the northern margin of the SCS and simulate their shape with elliptical cones. Results show that the total volume of these 45 seamounts above seafloor is estimated at about 1885–3078 km3 and the total volume of intrusive magma above Moho is about 0.15 Mkm3, which is close to the estimates for classic large igneous provinces across the world. These seamounts are mostly located on the continental slope with thin crust (approximately 12–18 km), which reduces the overlying pressure and shortens the magmatic conduits. The dominant azimuth of elliptical major axis in seamounts is consistent with the synrift and synspreading fault strikes (NE-NEE), indicating that these pre-existing faults provide magmatic conduits for the subsequent postrift intraplate seamounts. Based on three existing clues, i.e., (1) the intraplate seamounts, high velocity layer and Hainan mantle plume are contiguous in 3-D space, (2) the high velocity layer is thicker beneath the continental shelf but thinner beneath the slope and (3) the basalts dredged from certain seamounts show OIB-type geochemical features, we propose a magmatic upwelling pattern which contains Hainan mantle plume to explain the spatial and morphological characteristics of these intraplate seamounts.
      PubDate: 2017-05-30T11:15:56.473593-05:
      DOI: 10.1002/2016GC006792
  • Submarine landslides triggered by destabilization of high-saturation
           hydrate anomalies
    • Authors: Alexander L. Handwerger; Alan W. Rempel, Rob M. Skarbek
      Abstract: Submarine landslides occur along continental margins at depths that often intersect the gas hydrate stability zone, prompting suggestions that slope stability may be affected by perturbations that arise from changes in hydrate stability. Here, we develop a numerical model to identify the conditions under which the destabilization of hydrates results in slope failure. Specifically, we focus on high-saturation hydrate anomalies at fine- to coarse-grained stratigraphic boundaries that can transmit bridging stresses that decrease the effective stress at sediment contacts and disrupt normal sediment consolidation. We evaluate slope stability before and after hydrate destabilization. Hydrate anomalies act to significantly increase the overall slope stability due to large increases in effective cohesion. However, when hydrate anomalies destabilize there is a loss of cohesion and increase in effective stress that causes the sediment grains to rapidly consolidate and generate pore pressures that can either trigger immediate slope failure or weaken the surrounding sediment until the pore pressure diffuses away. In cases where failure does not occur, the sediment can remain weakened for months. In cases where failure does occur, we quantify landslide dynamics using a rate and state frictional model and find that landslides can display either slow or dynamic (i.e. catastrophic) motion depending on the rate-dependent properties, size of the stress perturbation, and the size of the slip patch relative to a critical nucleation length scale. Our results illustrate the fundamental mechanisms through which the destabilization of gas hydrates can pose a significant geohazard.
      PubDate: 2017-05-30T11:10:47.055013-05:
      DOI: 10.1002/2016GC006706
  • Contrasted hydrothermal activity along the South-East Indian Ridge
           (130°E–140°E): From crustal to ultramafic circulation
    • Authors: Cédric Boulart; Anne Briais, Valérie Chavagnac, Sidonie Révillon, Georges Ceuleneer, Jean-Pierre Donval, Vivien Guyader,
      Abstract: Using a combined approach of seafloor mapping, MAPR and CTD survey, we report evidence for active hydrothermal venting along the 130°-140°E section of the poorly-known South-East Indian Ridge (SEIR) from the Australia-Antarctic Discordance (AAD) to the George V Fracture Zone (FZ). Along the latter, we report Eh and CH4 anomalies in the water column above a serpentinite massif, which unambiguously testify for ultramafic-related fluid flow. This is the first time that such circulation is observed on an intermediate-spreading ridge. The ridge axis itself is characterized by numerous off-axis volcanoes, suggesting a high magma supply. The water column survey indicates the presence of at least ten distinct hydrothermal plumes along the axis. The CH4:Mn ratios of the plumes vary from 0.37 to 0.65 denoting different underlying processes, from typical basalt-hosted to ultramafic-hosted high-temperature hydrothermal circulation. Our data suggest that the change of mantle temperature along the SEIR not only regulates the magma supply, but also the hydrothermal activity. The distribution of hydrothermal plumes from a ridge segment to another implies secondary controls such as the presence of fractures and faults along the axis or in the axial discontinuities. We conclude from these results that hydrothermal activity along the SEIR is controlled by magmatic processes at the regional scale and by the tectonics at the segment scale, which influences the type of hydrothermal circulation and leads to various chemical compositions. Such variety may impact global biogeochemical cycles, especially in the Southern Ocean where hydrothermal venting might be the only source of nutrients.
      PubDate: 2017-05-30T11:10:43.007143-05:
      DOI: 10.1002/2016GC006683
  • A calcite reference material for LA-ICP-MS U-Pb geochronology
    • Authors: Nick M. W. Roberts; E. Troy Rasbury, Randall R Parrish, Christopher J Smith, Matthew S. A. Horstwood, Daniel J Condon
      Abstract: U-Pb dating of calcite is an emerging but rapidly growing field of application in geochronology with great potential to inform problems in landscape, basin and mountain belt evolution, through age determination of diagenetic cements, vein mineralisation and geological formations difficult to date otherwise. In this brief, we present isotope dilution U-Pb isotope measurements on a sample of calcite (WC-1) that has been and will continue to be used as a reference material for in-situ U-Pb Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) dating, and which is suitable to be distributed to the geochronological community. We present in-situ measurements using LA-ICP-MS to demonstrate the suitability of WC-1 for use as a U-Pb dating reference material, in spite of it not being isotopically homogeneous. The WC-1 calcite sample is 254.4 ± 6.4 Ma old, and comprised of 85 to 98% radiogenic lead. It presents a suitable reference material that can facilitate dating of calcite ranging in age from Precambrian to late Neogene age.
      PubDate: 2017-05-30T11:10:39.071915-05:
      DOI: 10.1002/2016GC006784
  • What happens to in-soil Radon activity during a long-lasting eruption?
           Insights from Etna by multidisciplinary data analysis
    • Authors: S. Falsaperla; M. Neri, G. Di Grazia, H. Langer, S. Spampinato
      Abstract: We analyze short- to long-term changes (from days to months) in Radon (Rn) activity measured nearby (
      PubDate: 2017-05-30T10:50:47.284909-05:
      DOI: 10.1002/2017GC006825
  • Multianalytical provenance analysis of eastern Ross Sea LGM till sediments
           (Antarctica): Petrography, geochronology, and thermochronology detrital
    • Authors: Matteo Perotti; Benedetta Andreucci, Franco Talarico, Massimiliano Zattin, Antonio Langone
      Abstract: In order to reveal provenance of detrital sediments supplied by West Antarctic Ice Sheet (WAIS), 19 glaciomarine cores of Last Glacial Maximum age were analyzed from Eastern Ross Sea and Sulzberger Bay. Analytical techniques included petrographic analysis of gravel-sized clasts, geochronology (zircon U-Pb: Zrn-UPb) and thermochronology (apatite fission track: AFT) of sand-sized fractions. Petrographic analysis revealed a similarity with the lithologies presently exposed in western Marie Byrd Land (MBL), with major roles played by low grade metamorphic rocks and granitoids. Furthermore Zrn-UPb and AFT data allowed to identify the ages of formation and cooling of sedimentary source area, consisting of Cambrian-Precambrian basement (i.e. Swanson Formation in western MBL) which underwent at least two episodes of magma intrusion, migmatization and cooling during Devonian-Carboniferous and Cretaceous-Paleocene times. Scarcity of volcanic clasts in the region of Ross Sea along the front of West Antarctica Ice Streams in association with the occurrence of AFT Oligocene-Pliocene dates suggests a localized tectonic exhumation of portions of MBL, as already documented for the opposite side of West Antarctic Rift System in the Transantarctic Mountains. Furthermore, a Zrn-UPb and AFT population of Late Triassic-Jurassic age indicates the presence of unexposed rocks that formed or metamorphosed at that time in the sedimentary source area, which could be identified in McAyeal Ice Stream and Bindschadler Ice Stream catchment areas.
      PubDate: 2017-05-30T10:50:44.215514-05:
      DOI: 10.1002/2016GC006728
  • The onset of modern-like Atlantic meridional overturning circulation at
           the Eocene-Oligocene transition: Evidence, causes, and possible
           implications for global cooling
    • Authors: Meir Abelson; Jonathan Erez
      Abstract: A compilation of benthic δ18O from the whole Atlantic and the Southern Ocean (Atlantic sector), shows two major jumps in the interbasinal gradient of δ18O (Δδ18O) during the Eocene and the Oligocene: One at ∼40 Ma and the second concomitant with the isotopic event of the Eocene-Oligocene transition (EOT), ∼33.7 Ma ago. From previously published circulation models and proxies, we show that the first Δδ18O jump reflects the thermal isolation of Antarctica associated with the proto-Antarctic circumpolar current (ACC). The second marks the onset of interhemispheric northern-sourced circulation cell, similar to the modern Atlantic meridional overturning circulation (AMOC). The onset of AMOC-like circulation slightly preceded (100-300 ky) the EOT, as we show by the high resolution profiles of δ18O and δ13C previously published from DSDP/ODP sites in the Southern Ocean and South Atlantic. These events coincide with the onset of anti-estuarine circulation between the Nordic seas and the North Atlantic which started around the EOT and may be connected to the deepening of the Greenland-Scotland Ridge. We suggest that while the shallow proto-ACC supplied the energy for deep ocean convection in the Southern Hemisphere, the onset of the interhemispheric northern circulation cell was due to the significant EOT intensification of deepwater formation in the North Atlantic driven by the Nordic anti-estuarine circulation. This onset of the interhemispheric northern-sourced circulation cell could have prompted the EOT global cooling.
      PubDate: 2017-05-30T10:50:37.306625-05:
      DOI: 10.1002/2017GC006826
  • Seismic structure and segmentation of the axial valley of the Mid-Cayman
           Spreading Center
    • Authors: Harm J.A. Van Avendonk; Nicholas W. Hayman, Jennifer L. Harding, Ingo Grevemeyer, Christine Peirce, Anke Dannowski
      Abstract: We report the results of a two-dimensional tomographic inversion of marine seismic refraction data from an array of ocean-bottom seismographs (OBSs), which produced an image of the crustal structure along the axial valley of the ultraslow-spreading Mid-Cayman Spreading Center (MCSC). The seismic velocity model shows variations in the thickness and properties of the young oceanic crust that are consistent with the existence of two magmatic-tectonic segments along the 110 km-long spreading center. Seismic wave speeds are consistent with exhumed mantle at the boundary between these two segments, but changes in the vertical gradient of seismic velocity suggest that volcanic crust occupies most of the axial valley seafloor along the seismic transect. The two spreading segments both have a low-velocity zone (LVZ) several kilometers beneath the seafloor, which may indicate the presence of shallow melt. However, the northern segment also has low seismic velocities (3 km/s) in a thick upper crustal layer (1.5-2.0 km), which we interpret as an extrusive volcanic section with high porosity and permeability. This segment hosts the Beebe vent field, the deepest known high-temperature black smoker hydrothermal vent system. In contrast, the southern spreading segment has seismic velocities as high as 4.0 km/s near the seafloor. We suggest that the porosity and permeability of the volcanic crust in the southern segment are much lower, thus limiting deep seawater penetration and hydrothermal recharge. This may explain why no hydrothermal vent system has been found in the southern half of the MCSC.
      PubDate: 2017-05-30T10:47:14.854635-05:
      DOI: 10.1002/2017GC006873
  • A kinetic model to explain the grainsize and organic matter content
           dependence of magnetic susceptibility in transitional marine environments:
           A case study in Ría de Muros (NW Iberia)
    • Authors: Kais J. Mohamed; Alba Andrade, Daniel Rey, Belén Rubio, Ana María Bernabeu
      Abstract: Magnetic minerals in marine sediments are sensitive indicators of processes such as provenance changes, climatic controls, pollution and postdepositional geochemical changes. Magnetic susceptibility is the bulk property of the sediments most commonly used to understand the magnetic characteristics of sediments. Before conclusions can be drawn from changes in this parameter, it is important to understand what factors and to what extent control changes in magnetic susceptibility. The magnetic susceptibility of surficial sediments in the Galician Rias Baixas, in NW Spain, has been shown to covary with sediment texture and organic matter content. Downcore, the magnetic properties of these sediments experience drastic changes as a result of strong dissolution caused by early diagenesis. In this paper, we further explore the relationship between these factors and formalise the observed covariations as the result of a simple second order kinetic model dependent on the content of organic matter in surficial sediments in the Ria de Muros. The reanalysis of previously reported data from the Rias de Vigo and Pontevedra confirmed the validity of this model, and suggested that further controls such as wave climate and water depth in the rates at which magnetic susceptibility changes are controlled by organic matter content.
      PubDate: 2017-05-30T10:46:57.98981-05:0
      DOI: 10.1002/2017GC006823
  • Geological interpretation of volcanism and segmentation of the Mariana
           back-arc spreading center between 12.7°N and 18.3°N
    • Authors: Melissa O. Anderson; William W. Chadwick, Mark D. Hannington, Susan G. Merle, Joseph A. Resing, Edward T. Baker, David A. Butterfield, Sharon L. Walker, Nico Augustin
      Abstract: The relationships between tectonic processes, magmatism, and hydrothermal venting along ∼600 km of the slow-spreading Mariana back-arc between 12.7°N and 18.3°N reveal a number of similarities and differences compared to slow-spreading mid-ocean ridges. Analysis of the volcanic geomorphology and structure highlights the complexity of the back-arc spreading center. Here, ridge segmentation is controlled by large-scale basement structures that appear to pre-date back-arc rifting. These structures also control the orientation of the chains of cross-arc volcanoes that characterize this region. Segment-scale faulting is oriented perpendicular to the spreading direction, allowing precise spreading directions to be determined. Four morphologically-distinct segment types are identified: dominantly magmatic segments (Type I); magmatic segments currently undergoing tectonic extension (Type II); dominantly tectonic segments (Type III); and tectonic segments currently undergoing magmatic extension (Type IV). Variations in axial morphology (including eruption styles, neovolcanic eruption volumes, and faulting) reflect magma supply, which is locally enhanced by cross-arc volcanism associated with N-S compression along the 16.5°N and 17.0°N segments. In contrast, cross-arc seismicity is associated with N-S extension and increased faulting along the 14.5°N segment, with structures that are interpreted to be oceanic core complexes—the first with high-resolution bathymetry described in an active back-arc basin. Hydrothermal venting associated with recent magmatism has been discovered along all segment types.
      PubDate: 2017-05-23T05:20:31.927232-05:
      DOI: 10.1002/2017GC006813
  • Halogen variations through the quenched margin of a MORB lava: Evidence
           for direct assimilation of seawater during eruption
    • Authors: Michael W. Broadley; Ray. Burgess, Hidenori. Kumagai, Natalie M. Curran, Chris J. Ballentine
      Abstract: Halogens and noble gases within submarine basaltic glasses are critical tracers of interactions between the surface volatile reservoirs and the mantle. However, as the halogens and noble gases are concentrated within seawater, sediments and the oceanic crust this makes the original volatile signature of submarine basaltic lavas susceptible to geochemical overprinting. This study combines halogen (Cl, Br and I), noble gas, and K concentrations within a single submarine basaltic quenched margin to quantify the amount of seawater assimilation during eruption, and to further elucidate the mechanisms of overprinting. The outer sections of the glass rim are enriched in Cl compared to the interior of the margin, which maintains mantle-like Br/Cl, I/Cl and K/Cl ratios. Low Br/Cl and K/Cl in the outer sections of the basaltic glass margin indicate that the Cl enrichment in the outer glass is derived from the assimilation of a saline brine component with up to 70% of the Cl within the glass being derived from brine assimilation. Atmospheric noble gas contamination is decoupled from halogen contamination with contaminated outer sections maintaining MORB-like 40Ar/36Ar, suggesting seawater derived brine assimilation during eruption is not the dominant source of atmospheric noble gases in submarine basalts. Volatile heterogeneities in submarine basalts introduced during and after eruption, as we have shown in this study, have the potential to expand the range of mantle halogen compositions and only by better understanding these heterogeneities can the Br/Cl and I/Cl variance in mantle derived samples be determined accurately.
      PubDate: 2017-05-22T05:35:41.410744-05:
      DOI: 10.1002/2016GC006711
  • Development of branching brittle and ductile shear zones: A numerical
    • Authors: Sven Erik Meyer; Boris Kaus, Cees Passchier
      Abstract: Continental collision zones are usually associated with large-scale strike-slip shear zones. In most cases these shear zones are complex and consist of multiple strands, varying in width, length, and total displacement. Here we present 2-D numerical models to simulate the formation of such shear zones at different depth levels within the crust, under either brittle (frictional/plastic) or ductile conditions. Localization of shear zones is initiated by a material contrast (heterogeneity) of the material parameters. We systematically test the rate of strain-weakening in brittle and in ductile regimes to understand its influence on the development of shear zone networks. Our simulations suggest that the development of antithetic faults in a brittle shear zone system is closely linked to a decrease in the angle of friction during deformation. In general, variation of the strain-weakening also has a significant influence on ductile shear zones. Numerical results show that the geometry and thickness of the localized high strain zone are especially affected by weakening mechanisms during deformation. Furthermore, the interconnection and interaction of the shear strands lead to a more complex kinematic pattern, which lead to a local change in the maximum principal stress axis. These interaction of shear strands may explain the occurrence of shear related structures (e.g. folds) or differing characteristics of shear zones, such as the thickness of shear zones or the orientation of the faults to the stress field, which are consistent with field observations.
      PubDate: 2017-05-22T05:25:54.060713-05:
      DOI: 10.1002/2016GC006793
  • Sand supply to the Lake Albert Basin (Uganda) during the Miocene-Pliocene:
           A multiproxy provenance approach
    • Authors: D. Gagnevin; S. Tyrrell, A.C. Morton, J. Leather, N. Lee, N. Bordas-Le Floch, D. Frei, J. Lukaye
      Abstract: A multi-proxy provenance approach (heavy mineral analysis, U-Pb zircon geochronology and Pb isotopic analysis of K-feldspar) has constrained sediment supply within the Upper Nile drainage system in the Miocene - Pliocene. Provenance data from sandstones were obtained from three exploration wells, two situated on the north-eastern margin and one on the eastern flank of the Lake Albert Basin, NW Uganda. Data suggest that high- to low-grade metamorphic rocks and granitoids have variably supplied the heavy mineral assemblages around the Lake Albert Basin during the Miocene-Pliocene, with contributions from the isotopically-heterogeneous Archean Cratons (including the local Ugandan Craton, Tanzanian and Congo Cratons) and the Pan-African rocks (the Mozambique Belt) with possible contributions from the Neoproterozoic and Paleoproterozoic rocks. These data also highlight clear differences between supply to the eastern basin margin, compared with the northeast, which is reconcilable with current models for Miocene-Pliocene drainage in the region. Supply to northeastern Lake Albert during the Miocene-Pliocene appears to have been through a proto-Albert Nile (draining from NE to SW) and from a proto-Victoria Nile or similarly oriented palaeo-river systems draining from the east. In contrast, the eastern flanks of the basin were likely supplied via the palaeo-Nkusi river, tapping local hinterland sources and more distal basement to the far-east (Mozambique Belt). This study highlights the importance of utilizing a multi-proxy approach in provenance analysis as no one signal is capable of distinguishing the different source lands and constraining the evolving drainage patterns.
      PubDate: 2017-05-22T05:20:46.257961-05:
      DOI: 10.1002/2016GC006650
  • Rock magnetic and geochemical evidence for authigenic magnetite formation
           via iron reduction in coal-bearing sediments offshore Shimokita Peninsula,
           Japan (IODP Site C0020)
    • Authors: Stephen C. Phillips; Joel E. Johnson, William C. Clyde, Jacob B. Setera, Daniel P. Maxbauer, Silke Severmann, Natascha Riedinger
      Abstract: Sediments recovered at Integrated Ocean Drilling Program (IODP) Site C0020, in a forearc basin offshore Shimokita Peninsula, Japan, include numerous coal beds (0.3 – 7 m thick) that are associated with a transition from a terrestrial to marine depositional environment. Within the primary coal-bearing unit (∼2 km depth below seafloor) there are sharp increases in magnetic susceptibility in close proximity to the coal beds, superimposed on a background of consistently low magnetic susceptibility throughout the remainder of the recovered stratigraphic sequence. We investigate the source of the magnetic susceptibility variability and characterize the dominant magnetic assemblage throughout the entire cored record, using isothermal remanent magnetization (IRM), thermal demagnetization, anhysteretic remanent magnetization (ARM), iron speciation, and iron isotopes. Magnetic mineral assemblages in all samples are dominated by very low-coercivity minerals with unblocking temperatures between 350-580°C that are interpreted to be magnetite. Samples with lower unblocking temperatures (300-400°C), higher ARM, higher frequency dependence, and isotopically heavy δ56Fe across a range of lithologies in the coal-bearing unit (between 1925-1995 mbsf), indicate the presence of fine-grained authigenic magnetite. We suggest that iron-reducing bacteria facilitated the production of fine-grained magnetite within the coal-bearing unit during burial and interaction with pore waters. The coal/peat acted as a source of electron donors during burial, mediated by humic acids, to supply iron reducing bacteria in the surrounding siliciclastic sediments. These results indicate that coal-bearing sediments may play an important role in iron cycling in subsiding peat environments and if buried deeply through time, within the subsequent deep biosphere.
      PubDate: 2017-05-22T05:20:42.482476-05:
      DOI: 10.1002/2017GC006943
  • A CO2-gas precursor to the March 2015 Villarrica volcano eruption
    • Authors: Alessandro Aiuppa; Marcello Bitetto, Vincenzo Francofonte, Gabriela Velasquez, Claudia Bucarey Parra, Gaetano Giudice, Marco Liuzzo, Roberto Moretti, Yves Moussallam, Nial Peters, Giancarlo Tamburello, Oscar. A. Valderrama, Aaron Curtis
      Abstract: We present here the first volcanic gas compositional time-series taken prior to a paroxysmal eruption of Villarrica volcano (Chile). Our gas plume observations were obtained using a fully autonomous Multi-component Gas Analyser System (Multi-GAS) in the 3 month-long phase of escalating volcanic activity that culminated into the March 3 2015 paroxysm, the largest since 1985. Our results demonstrate a temporal evolution of volcanic plume composition, from low CO2/SO2 ratios (0.65-2.7) during November 2014-January 2015 to CO2/SO2 ratios up to ≈ 9 then after. The H2O/CO2 ratio simultaneously declined to
      PubDate: 2017-05-22T05:20:40.074385-05:
      DOI: 10.1002/2017GC006892
  • Pervasive silicification and hanging wall overplating along the 13°20'N
           oceanic detachment fault (Mid-Atlantic Ridge)
    • Authors: D. Bonnemains; J. Escartín, C. Mével, M. Andreani, A. Verlaguet
      Abstract: The corrugated detachment fault zone of the active 13°20'N oceanic core complex (Mid Atlantic Ridge) was investigated with a deep-sea vehicle to assess the links between deformation, alteration, and magmatism at detachment fault zones. We present a study of eighteen in-situ fault rock samples from striated fault outcrops on the flanks of microbathymetric corrugations. All the samples are mafic breccias that are mostly derived from a diabase protolith, with two of them also showing mixing with ultramafic clasts. Breccias are cataclastic and display variable deformation textures, recording numerous slip events, and showing pervasive silicification throughout the fault zone. Deformation-silicification relationships are also complex, showing both static and syntectonic quartz precipitation; undeformed quartz overprints the fault breccia textures, and reflective and striated fault surfaces cross-cut silicified rocks. In-situ detachment fault rocks are mainly fault breccias with almost exclusively basaltic clasts, with rare ultramafic ones, a lithology and texture never observed previously at other oceanic detachment fault zones. We propose the lower dyke complex in the hanging wall crust at the volcanic rift valley floor is the most plausible diabase source. Mechanical mixing of predominantly mafic and rare ultramafic clasts suggests an underlying ultramafic footwall, and that mafic accretion operates in the shallowest crust (1-2 km), at the base of the dyke complex at temperatures >400°C. Silicification is produced by silica-rich fluids syntectonically channeled along the fault zone, and likely derived from hydrothermal alteration of basaltic rocks, likely mixed with serpentinization-derived fluids.
      PubDate: 2017-05-22T05:20:34.069562-05:
      DOI: 10.1002/2017GC006846
  • Short-term variations of Icelandic ice cap mass inferred from cGPS
           coordinate time series
    • Authors: Kathleen Compton; Richard A. Bennett, Sigrún Hreinsdóttir, Tonie van Dam, Andrea Bordoni, Valentina Barletta, Giorgio Spada
      Abstract: As the global climate changes, understanding short-term variations in water storage is increasingly important. Continuously operating Global Positioning System (cGPS) stations in Iceland record annual periodic motion – the elastic response to winter accumulation and spring melt seasons – with peak-to-peak vertical amplitudes over 20 mm for those sites in the Central Highlands. Here, for the first time for Iceland, we demonstrate the utility of these cGPS-measured displacements for estimating seasonal and shorter-term ice cap mass changes. We calculate unit responses to each of the five largest ice caps in central Iceland at each of the 62 cGPS locations using an elastic half-space model and estimate ice mass variations from the cGPS time series using a simple least squares inversion scheme. We utilize all three components of motion, taking advantage of the seasonal motion recorded in the horizontal. We remove secular velocities and accelerations and explore the impact that seasonal motions due to atmospheric, hydrologic, and non-tidal ocean loading have on our inversion results. Our results match available summer and winter mass balance measurements well, and we reproduce the seasonal stake-based observations of loading and melting within the 1σ confidence bounds of the inversion. We identify non-periodic ice mass changes associated with interannual variability in precipitation and other processes such as increased melting due to reduced ice surface albedo or decreased melting due to ice cap insulation in response to tephra deposition following volcanic eruptions, processes that are not resolved with once- or twice- yearly stake measurements.
      PubDate: 2017-05-22T05:20:29.304937-05:
      DOI: 10.1002/2017GC006831
  • The formation of gold-rich seafloor sulfide deposits: Evidence from the
           Beebe Hydrothermal Vent Field, Cayman Trough
    • Authors: Alexander P. Webber; Stephen Roberts, Bramley J. Murton, Rachel A. Mills, Matthew R. S. Hodgkinson
      Abstract: The Beebe vent field (BVF) in the Cayman Trough has built an auriferous massive sulfide deposit on the ultra-slow spreading mid-Cayman spreading centre. The genesis of auriferous sulfide deposits at mid-ocean ridges is not fully understood, although there is a growing recognition that slow and ultra-slow spreading centres are conducive to gold mineralization. Analysis of hydrothermal precipitates from the BVF indicates that the highest gold contents are present within “beehive diffusers”, which have developed a highly porous pyrrhotite framework. The beehive structure allows vent fluids to effuse slowly, while allowing ingress of seawater to cool the fluid. The prevalence of pyrrhotite in the beehive samples, lack of sulfates, association between pyrrhotite and gold grains, and results of thermodynamic modelling, suggests gold precipitation occurred under highly reduced conditions even during mixing with seawater. In contrast, high temperature chimneys, with a single orifice, maintain high temperatures to the primary vent orifice and much of the gold is lost to seawater. Despite this, both chimney types are relatively gold enriched, which points to a further underlying cause for high gold at the BVF such as interaction of hydrothermal fluids with ultramafic lithologies in the basement. The final gold composition of the deposit is partially controlled by loss of gold during mass-wasting of the material, with gold depletion most prevalent in blocks formed at beehive-type chimneys. The BVF demonstrates that the overall gold content of a massive sulfide deposit is the sum of basement, precipitation, and surface processes.
      PubDate: 2017-05-08T04:50:44.982809-05:
      DOI: 10.1002/2017GC006922
  • Superweak asthenosphere in light of upper mantle seismic anisotropy
    • Authors: Thorsten W. Becker
      Abstract: Earth's upper mantle includes a ∼ 200 km thick asthenosphere underneath the plates where viscosity and seismic velocities are reduced compared to the background. This zone of weakness matters for plate dynamics and may be required for the generation of plate tectonics itself. However, recent seismological and electro-magnetic studies indicate strong heterogeneity in thinner layers underneath the plates which, if related to more extreme, global viscosity reductions, may require a revision of our understanding of mantle convection. Here, I use dynamically-consistent mantle flow modeling and the constraints provided by azimuthal seismic anisotropy as well as plate motions to explore the effect of a range of global and local viscosity reductions. The fit between mantle flow model predictions and observations of seismic anisotropy is highly sensitive to radial and lateral viscosity variations. I show that moderate sub-oceanic viscosity reductions, to ∼ 0.01 to 0.1 times the upper mantle viscosity, are preferred by the fit to anisotropy and global plate motions, depending on layer thickness. Lower viscosities degrade the fit to azimuthal anisotropy. Localized patches of viscosity reduction, or layers of subducted asthenosphere, however, have only limited additional effects on anisotropy or plate velocities. This indicates that it is unlikely that regional observations of sub-plate anomalies are both continuous and indicative of dramatic viscosity reduction. Locally, such weak patches may exist and would be detectable by regional anisotropy analysis, for example. However, large-scale plate dynamics are most likely governed by broad continent-ocean asthenospheric viscosity contrasts rather than a thin, possibly high melt fraction layer.
      PubDate: 2017-04-27T15:07:22.512707-05:
      DOI: 10.1002/2017GC006886
  • Understanding volcanic hazard at the most populated caldera in the world:
           Campi Flegrei, Southern Italy
    • Authors: Giuseppe De Natale; Claudia Troise, Christopher R.J. Kilburn, Renato Somma, Roberto Moretti
      Abstract: Naples and its hinterland in Southern Italy are one of the most urbanized areas in the world under threat from volcanic activity. The region lies within range of three active volcanic centers: Vesuvius, Campi Flegrei, and Ischia. The Campi Flegrei caldera, in particular, has been in unrest for six decades. The unrest followed four centuries of quiescence and has heightened concern about an increased potential for eruption. Innovative modelling and scientific drilling are being used to investigate Campi Flegrei, and the results highlight key directions for better understanding the mechanisms of caldera formation and the roles of magma intrusion and geothermal activity in determining the volcano's behavior. They also provide a framework for evaluating and mitigating the risk from this caldera and other large ones worldwide.
      PubDate: 2017-04-20T09:00:07.038048-05:
      DOI: 10.1002/2017GC006972
  • Seafloor age dependence of Rayleigh wave phase velocities in the Indian
    • Authors: Karen E. Godfrey; Colleen A. Dalton, Jeroen Ritsema
      Abstract: Variations in the phase velocity of fundamental-mode Rayleigh waves across the Indian Ocean are determined using two inversion approaches. First, variations in phase velocity as a function of seafloor age are estimated using a pure-path age-dependent inversion method. Second, a two-dimensional parameterization is used to solve for phase velocity within 1.25° × 1.25° grid cells. Rayleigh wave travel-time delays have been measured between periods of 38 and 200 s. The number of measurements in the study area ranges between 4139 paths at a period of 200 s and 22,272 paths at a period of 40 s. At periods 
      PubDate: 2017-04-18T15:46:04.860724-05:
      DOI: 10.1002/2017GC006824
  • Possible sources of hydrothermal activity and mud volcanism in southern
           Sakhalin inferred from local earthquake seismic tomography
    • Authors: Ivan Koulakov; Aleksander S. Serdyukov, Alexey V. Konovalov, Valentin I. Mikhailov, Dmitry A. Safonov, Anton A. Duchkov, Nassir Al-Arifi, Sami El Khrepy
      Abstract: We present the first seismic model of the crust beneath Sakhalin based on P- and S-wave arrival time data from local earthquakes. Based on the results of numerous synthetic tests, we conclude that this model has fair horizontal and vertical resolution to 20–25 km depth. At shallow depths, seismic anomalies are clearly associated with known geological structures, such as the high-velocity Paleozoic Susunai block and the low-velocity Cenozoic fold belts along the West Sakhalin Mountains. In vertical sections, we observe westward underthrusting of the Susunai block to a distance of at least 70 km, which may represent the regional compression and considerable crustal shortening in this area. Based on the tomography results, we hypothesize about the origin of the mud volcanism in southern Sakhalin. We propose that because of the general westward underthrusting regime in Sakhalin, hydrocarbon-rich shelf sediments may be entrained to considerable depths under the rigid Susunai block, which serves as a non-permeable cover. The released gases find the weakest zones around the Susunai block and along the Tym-Poronay Fault and escape to the surface to form the South Sakhalin and Lesnovsky mud volcano fields.
      PubDate: 2017-04-18T15:45:34.823377-05:
      DOI: 10.1002/2017GC006820
  • Can high-temperature, high-heat flux hydrothermal vent fields be explained
           by thermal convection in the lower crust along fast spreading mid-ocean
    • Authors: Fabrice J. Fontaine; M. Rabinowicz, M. Cannat
      Abstract: We present numerical models to explore possible couplings along the axis of fast spreading ridges, between hydrothermal convection in the upper crust, and magmatic flow in the lower crust. In an end-member category of models corresponding to effective viscosities μM lower than 1013 Pa.s in a melt-rich lower crustal along-axis corridor and permeability k not exceeding ∼10−16 m2 in the upper crust, the hot, melt-rich, gabbroic lower crust convects as a viscous fluid, with convection rolls parallel to the ridge axis. In these models, we show that the magmatic-hydrothermal interface settles at realistic depths for fast ridges, i.e. 1-2 km below seafloor. Convection cells in both horizons are strongly coupled and km-wide hydrothermal upflows/plumes, spaced by 8-10 km, arise on top of the magmatic upflows. Such magmatic-hydrothermal convective couplings may explain the distribution of vent fields along the East (EPR) and South-East Pacific Rise (SEPR). The lower crustal plumes deliver melt locally at the top of the magmatic horizon possibly explaining the observed distribution of melt-rich regions/pockets in the axial melt lenses of EPR and SEPR. Crystallization of this melt provides the necessary latent heat to sustain permanent ∼100 MW vents fields. Our models also contribute to current discussions on how the lower crust forms at fast ridges: they provide a possible mechanism for focused transport of melt-rich crystal mushes from moho level to the axial melt lens where they further crystallize, feed eruptions and are transported both along and off-axis to produce the lower crust.
      PubDate: 2017-04-18T15:45:31.656303-05:
      DOI: 10.1002/2016GC006737
  • Rock record and magnetic response to large earthquakes within Wenchuan
           Earthquake Fault Scientific Drilling cores
    • Authors: Lei Zhang; Zhiming Sun, Haibing Li, Laishi Zhao, Sheng-Rong Song, Yu-Min Chou, Yong Cao, Xiaozhou Ye, Huan Wang, Xiangli He
      Abstract: Fault-related pseudotachylytes are often considered to be produced by large seismic events. To investigate the rock record and magnetic response to large earthquakes within cores from the Wenchuan Earthquake Fault Scientific Drilling borehole 2 (WFSD-2), we carried out microstructural, geochemical and rock magnetic analyses of representative cores. Based on microstructural observations and powder X-ray diffraction analyses, we found 21 layers of melt-origin pseudotachylytes from 579.62–599.31 m-depth in the cores. The presence of early-formed pseudotachylyte fragments in the new layer suggests that seismic faulting processes exploited the same fault strand more than once. Pseudotachylyte veins have higher values of magnetic susceptibility relative to wall rocks. Rock magnetic results indicate that the magnetic minerals within the pseudotachylyte veins are magnetite with varying amounts of paramagnetic minerals. Magnetic hysteresis loops show that a reduction of the grain-size of ferromagnetic minerals is not a plausible explanation for the higher magnetic susceptibility values in pseudotachylyte veins. Rock magnetic analyses indicate that frictional heating (>500°C) occurred in the pseudotachylyte veins during large earthquakes. The resulting high temperatures induced thermal decomposition of paramagnetic minerals, forming magnetite and contributing to the higher magnetic susceptibility values. Different generations of pseudotachylytes and numerous high magnetic susceptibility zones together demonstrate that ancient powerful earthquakes may have occurred repeatedly in the Longmen Shan thrust belt.
      PubDate: 2017-04-12T14:17:43.058504-05:
      DOI: 10.1002/2017GC006822
  • 3-D basin-scale reconstruction of natural gas hydrate system of the Green
           Canyon, Gulf of Mexico
    • Authors: Ewa Burwicz; Thomas Reichel, Klaus Wallmann, Wolf Rottke, Matthias Haeckel, Christian Hensen
      Abstract: Our study presents a basin-scale 3D modeling solution, quantifying and exploring gas hydrate accumulations in the marine environment around the Green Canyon (GC955) area, Gulf of Mexico. It is the first modeling study that considers the full complexity of gas hydrate formation in a natural geological system. Overall, it comprises a comprehensive basin re-construction, accounting for depositional and transient thermal history of the basin, source rock maturation, petroleum components generation, expulsion and migration, salt tectonics and associated multi-stage fault development. The resulting 3D gas hydrate distribution in the Green Canyon area is consistent with independent borehole observations. An important mechanism identified in this study and leading to high gas hydrate saturation (> 80 vol. %) at the base of the gas hydrate stability zone (GHSZ), is the recycling of gas hydrate and free gas enhanced by high Neogene sedimentation rates in the region. Our model predicts the rapid development of secondary intra-salt mini-basins situated on top of the allochthonous salt deposits which leads to significant sediment subsidence and an ensuing dislocation of the lower GHSZ boundary. Consequently, large amounts of gas hydrates located in the deepest parts of the basin dissociate and the released free methane gas migrates upwards to recharge the GHSZ. In total, we have predicted the gas hydrate budget for the Green Canyon area that amounts to ∼3,256 Mt of gas hydrate which is equivalent to ∼340 Mt of carbon (∼7 x 1011 m3 of CH4 at STP conditions), and consists mostly of biogenic hydrates.
      PubDate: 2017-04-12T14:14:51.098131-05:
      DOI: 10.1002/2017GC006876
  • Evolution of the South Pacific helium plume over the past 3 decades
    • Authors: J.E. Lupton; W.J. Jenkins
      Abstract: The recent GEOTRACES Eastern Pacific Zonal Transect in 2013 crossed the East Pacific Rise at 15°S following the same track as the 1987 Helios Expedition along the core of the mid-depth helium plume that spreads westward from the East Pacific Rise (EPR) axis. The fact that several stations were co-located with the earlier Helios stations has allowed a detailed comparison of the changes in the helium plume over the intervening 26 years. While the plume in many areas is unchanged, there is a marked decrease in plume intensity at longitude 120°W in the 2013 data which was not present in 1987. Recent radioisotope measurements along the plume track suggest that this decrease is due to the intrusion of a different water mass into the plume, rather than a modulation of hydrothermal input on the EPR axis. Analysis of GEOTRACES hydrographic data shows excess heat present in the plume up to 0.04°C, corresponding to a 3He/heat ratio of ∼2.5 × 10−18 mol J−1, similar to that found in mature hydrothermal vents. RAFOS floats deployed in 1987 indicate an average westward transport of ∼0.3 cm s−1 at 2500 m depth in the off-axis plume, in agreement with recent estimates of ∼0.4 cm s−1 based on “aging” of the plume from 227Ac/3He ratios.
      PubDate: 2017-04-12T14:12:32.435656-05:
      DOI: 10.1002/2017GC006848
  • Natural H2 in Kansas: Deep or shallow origin?
    • Authors: J. Guélard; V. Beaumont, V. Rouchon, F. Guyot, D. Pillot, D. Jézéquel, M. Ader, K. D. Newell, E. Deville
      Abstract: A geochemical study of gas coming from three wells in northeastern Kansas supplements previous studies from the 1980s and points to a persistent regional phenomenon of H2 production. In 2008, a new well showed, just after drilling, a free gas phase with more than 80 mole % of H2, followed by water production associated with gas. This gas is mainly composed of N2, He, H2 and occasionally CH4, with changing proportions through time. A drastic decrease in H2 at the well was observed since the aquifer is produced, along with occasional recharges in H2 evidenced notably in the early phases of gas sampling. We demonstrate that this evolution of gas composition is closely associated to the well completion story. Accordingly, two distinct origins of H2 are proposed: (1) deep crustal H2: water reduction associated to iron oxidation in the Precambrian basement; (2) reactions occurring in the tubing, primarily attributed to high contents of reduced iron and/or dissolved organic carbon (DOC=4.1 mg.L−1) in the water. The low δD values averaging -760 ‰ are attributed to a low temperature process, possibly a re-equilibration with water. Furthermore, the suggested origins are supported by the observed gas associations: (a) deep crustal H2 with radiogenic gases (4He and 40Ar) and metamorphic N2 (δ15N averaging +2.5‰); (b) surficial H2 with methane produced in the sedimentary aquifer and the tubing by methanogenic organisms.
      PubDate: 2017-04-03T02:41:08.147781-05:
      DOI: 10.1002/2016GC006544
  • Shallow melting of MORB-like mantle under hot continental lithosphere,
           Central Anatolia
    • Authors: Mary R. Reid; W. Kirk Schleiffarth, Michael A. Cosca, Jonathan R. Delph, Janne Blichert-Toft, Kari M. Cooper
      Abstract: Widespread mafic volcanism, elevated crustal temperatures, and plateau-type topography in Central Anatolia, Turkey, could collectively be the result of lithospheric delamination, mantle upwelling, and tectonic escape. We use results from 40Ar/39Ar geochronology, basalt geochemistry, and a passive-source broadband seismic experiment obtained in a collaborative international effort (Continental Dynamics – Central Anatolia Tectonics) to investigate the upper mantle structure and evolution of melting conditions over an ∼2400 km2 area south and west of Hasan volcano. New 40Ar/39Ar dates for the basalts mostly cluster between 0.2 and 0.6 Ma, but some scoria cones are as old as 2.5 Ma. Basalts are dominantly Mg-rich (Mg#=62 to 71), moderately alkaline (normative Ne
      PubDate: 2017-04-03T02:35:57.642899-05:
      DOI: 10.1002/2016GC006772
  • Lithospheric structure of Iberia and Morocco using finite-frequency
           Rayleigh wave tomography from earthquakes and seismic ambient noise
    • Authors: I. Palomeras; A. Villaseñor, S. Thurner, A. Levander, J. Gallart, M. Harnafi
      Abstract: We present a new 3D shear velocity model of the western Mediterranean from the Pyrenees, Spain, to the Atlas Mountains, Morocco, and the estimated crustal and lithospheric thickness. The velocity model shows different crustal and lithospheric velocities for the Variscan provinces, those which have been affected by Alpine deformation, and those which are actively deforming. The Iberian Massif has detectable differences in crustal thickness that can be related to the evolution of the Variscan orogen in Iberia. Areas affected by Alpine deformation have generally lower velocities in the upper and lower crust than the Iberian Massif. Beneath the Gibraltar Strait and surrounding areas the crustal thickness is greater than 50 km, below which a high velocity anomaly (>4.5 km/s) is mapped to depths greater than 200 km. We identify this as a subducted remnant of the NeoTethys plate referred to as the Alboran and western Mediterranean slab. Beneath the adjacent Betic and Rif Mountains, the Alboran slab is still attached to the base of the crust, depressing it, and ultimately delaminating the lower crust and mantle lithosphere as the slab sinks. Under the adjacent continents the Alboran slab is surrounded by low upper mantle shear wave velocities (Vs
      PubDate: 2017-03-28T11:00:29.795201-05:
      DOI: 10.1002/2016GC006657
  • Differential response of corals to regional mass-warming events as evident
           from skeletal Sr/Ca and Mg/Ca ratios
    • Authors: Harry Clarke; Juan Pablo D'Olivo, James Falter, Jens Zinke, Ryan Lowe, Malcolm McCulloch
      Abstract: During the summer of 2010/11, a regional marine heat wave resulted in coral bleaching of variable severity along much of the western coastline of Australia. At Ningaloo Reef, a 300km long fringing reef system and World Heritage site, highly contrasting coral bleaching was observed between two morphologically distinct nearshore reef communities located on either side of the Ningaloo Peninsula: Tantabiddi (∼20% bleaching) and Bundegi (∼90% bleaching). For this study, we collected coral cores (Porites sp.) from Tantabiddi and Bundegi reef sites to assess the response of the Sr/Ca temperature proxy and Mg/Ca ratios to the variable levels of thermal stress imposed at these two sites during the 2010/11 warming event. We found that there was an anomalous increase in Sr/Ca and decrease in Mg/Ca ratios in the Bundegi record that was coincident with the timing of severe coral bleaching at the site, while no significant changes were observed in the Tantabiddi record. We show that the change in the relationship of Sr/Ca and Mg/Ca ratios with temperature at Bundegi during the 2010/11 event reflects changes in related coral ‘vital' processes during periods of environmental stress. These changes were found to be consistent with a reduction in active transport of Ca2+ to the site of calcification leading to a reduction in calcification rates and reduced Rayleigh fractionation of incorporated trace elements. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-17T19:20:26.74265-05:0
      DOI: 10.1002/2016GC006788
  • Issue Information
    • Pages: 1793 - 1793
      PubDate: 2017-06-15T04:03:24.504337-05:
      DOI: 10.1002/ggge.21121
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