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Geochemistry, Geophysics, Geosystems: G³

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https://www.readbyqxmd.com/read/30166946/seismic-imaging-of-thickened-lithosphere-resulting-from-plume-pulsing-beneath-iceland
#1
Catherine A Rychert, Nicholas Harmon, John J Armitage
Ocean plates conductively cool and subside with seafloor age. Plate thickening with age is also predicted, and hot spots may cause thinning. However, both are debated and depend on the way the plate is defined. Determining the thickness of the plates along with the process that governs it has proven challenging. We use S-to-P (Sp) receiver functions to image a strong, persistent LAB beneath Iceland where the mid-Atlantic Ridge interacts with a plume with hypothesized pulsating thermal anomaly. The plate is thickest, up to 84 ± 6 km, beneath lithosphere formed during times of hypothesized hotter plume temperatures and as thin as 61 ± 6 km beneath regions formed during colder intervals...
June 2018: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/30174559/submachine-web-based-tools-for-exploring-seismic-tomography-and-other-models-of-earth-s-deep-interior
#2
Kasra Hosseini, Kara J Matthews, Karin Sigloch, Grace E Shephard, Mathew Domeier, Maria Tsekhmistrenko
We present SubMachine, a collection of web-based tools for the interactive visualization, analysis, and quantitative comparison of global-scale data sets of the Earth's interior. SubMachine focuses on making regional and global-scale seismic tomography models easily accessible to the wider solid Earth community, in order to facilitate collaborative exploration. We have written software tools to visualize and explore over 30 tomography models-individually, side-by-side, or through statistical and averaging tools...
May 2018: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/30344451/magnetism-at-depth-a-view-from-an-ancient-continental-subduction-and-collision-zone
#3
Suzanne A McEnroe, Peter Robinson, Nathan Church, Michael Purucker
Recent sophisticated global data compilations and magnetic surveys have been used to investigate the nature of magnetization in the lower crust and upper mantle. Two approaches to constraining magnetizations are developed, providing minimum (0.01 SI) and maximum (0.04 SI) susceptibility estimates, given some assumed thickness (15+ km here). These values are higher than are found in many continental rocks. Are there rocks deeper in the crust or upper mantle that are more magnetic than expected, or are the model assumptions incomplete? What is the magnetic behavior of deep crustal and upper mantle rocks, when slightly cooler than the Curie or Néel temperatures of their magnetic minerals, after being exhumed from locations of high-grade metamorphism at greater depth? Different sets of equilibrium metamorphic minerals can be considered that would form under different conditions...
April 2018: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/29937699/merrill-micromagnetic-earth-related-robust-interpreted-language-laboratory
#4
Pádraig Ó Conbhuí, Wyn Williams, Karl Fabian, Phil Ridley, Lesleis Nagy, Adrian R Muxworthy
Complex magnetic domain structures and the energy barriers between them are responsible for pseudo-single-domain phenomena in rock magnetism and contribute significantly to the magnetic remanence of paleomagnetic samples. This article introduces MERRILL, an open source software package for three-dimensional micromagnetics optimized and designed for the calculation of such complex structures. MERRILL has a simple scripting user interface that requires little computational knowledge to use but provides research strength algorithms to model complex, inhomogeneous domain structures in magnetic materials...
April 2018: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/29937698/characterization-by-scanning-precession-electron-diffraction-of-an-aggregate-of-bridgmanite-and-ferropericlase-deformed-at-hp-ht
#5
B C Nzogang, J Bouquerel, P Cordier, A Mussi, J Girard, S Karato
Scanning precession electron diffraction is an emerging promising technique for mapping phases and crystal orientations with short acquisition times (10-20 ms/pixel) in a transmission electron microscope similarly to the Electron Backscattered Diffraction (EBSD) or Transmission Kikuchi Diffraction (TKD) techniques in a scanning electron microscope. In this study, we apply this technique to the characterization of deformation microstructures in an aggregate of bridgmanite and ferropericlase deformed at 27 GPa and 2,130 K...
March 2018: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/29097907/constraints-on-the-anisotropic-contributions-to-velocity-discontinuities-at-%C3%A2-60-km-depth-beneath-the-pacific
#6
Catherine A Rychert, Nicholas Harmon
Strong, sharp, negative seismic discontinuities, velocity decreases with depth, are observed beneath the Pacific seafloor at ∼60 km depth. It has been suggested that these are caused by an increase in radial anisotropy with depth, which occurs in global surface wave models. Here we test this hypothesis in two ways. We evaluate whether an increase in surface wave radial anisotropy with depth is robust with synthetic resolution tests. We do this by fitting an example surface wave data set near the East Pacific Rise...
August 2017: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/27917071/a-distinct-source-and-differentiation-history-for-kolumbo-submarine-volcano-santorini-volcanic-field-aegean-arc
#7
Martijn Klaver, Steven Carey, Paraskevi Nomikou, Ingrid Smet, Athanasios Godelitsas, Pieter Vroon
This study reports the first detailed geochemical characterization of Kolumbo submarine volcano in order to investigate the role of source heterogeneity in controlling geochemical variability within the Santorini volcanic field in the central Aegean arc. Kolumbo, situated 15 km to the northeast of Santorini, last erupted in 1650 AD and is thus closely associated with the Santorini volcanic system in space and time. Samples taken by remotely-operated vehicle that were analyzed for major element, trace element and Sr-Nd-Hf-Pb isotope composition include the 1650 AD and underlying K2 rhyolitic, enclave-bearing pumices that are nearly identical in composition (73 wt...
August 2016: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/27656115/increased-rates-of-large-magnitude-explosive-eruptions-in-japan-in-the-late-neogene-and-quaternary
#8
S H Mahony, R S J Sparks, L M Wallace, S L Engwell, E M Scourse, N H Barnard, J Kandlbauer, S K Brown
Tephra layers in marine sediment cores from scientific ocean drilling largely record high-magnitude silicic explosive eruptions in the Japan arc for up to the last 20 million years. Analysis of the thickness variation with distance of 180 tephra layers from a global data set suggests that the majority of the visible tephra layers used in this study are the products of caldera-forming eruptions with magnitude (M) > 6, considering their distances at the respective drilling sites to their likely volcanic sources...
July 2016: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/27570497/orbitally-paced-phosphogenesis-in-mediterranean-shallow-marine-carbonates-during-the-middle-miocene-monterey-event
#9
Gerald Auer, Christoph A Hauzenberger, Markus Reuter, Werner E Piller
During the Oligo-Miocene, major phases of phosphogenesis occurred in the Earth's oceans. However, most phosphate deposits represent condensed or allochthonous hemipelagic deposits, formed by complex physical and chemical enrichment processes, limiting their applicability for the study regarding the temporal pacing of Miocene phosphogenesis. The Oligo-Miocene Decontra section located on the Maiella Platform (central Apennines, Italy) is a widely continuous carbonate succession deposited in a mostly middle to outer neritic setting...
April 2016: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/27570496/fluid-inclusion-petrology-and-microthermometry-of-the-cocos-ridge-hydrothermal-system-iodp-expedition-344-crisp-2-site-u1414
#10
Jennifer Brandstätter, Walter Kurz, Kurt Krenn, Peter Micheuz
In this study, we present new data from microthermometry of fluid inclusions entrapped in hydrothermal veins along the Cocos Ridge from the IODP Expedition 344 Site U1414. The results of our study concern a primary task of IODP Expedition 344 to evaluate fluid/rock interaction linked with the tectonic evolution of the incoming Cocos Plate from the Early Miocene up to recent times. Aqueous, low saline fluids are concentrated within veins from both the Cocos Ridge basalt and the overlying lithified sediments of Unit III...
April 2016: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/30123099/linkages-between-mineralogy-fluid-chemistry-and-microbial-communities-within-hydrothermal-chimneys-from-the-endeavour-segment-juan-de-fuca-ridge
#11
T J Lin, H C Ver Eecke, E A Breves, M D Dyar, J W Jamieson, M D Hannington, H Dahle, J L Bishop, M D Lane, D A Butterfield, D S Kelley, M D Lilley, J A Baross, J F Holden
Rock and fluid samples were collected from three hydrothermal chimneys at the Endeavour Segment, Juan de Fuca Ridge to evaluate linkages among mineralogy, fluid chemistry, and microbial community composition within the chimneys. Mössbauer, midinfrared thermal emission, and visible-near infrared spectroscopies were utilized for the first time to characterize vent mineralogy, in addition to thin-section petrography, X-ray diffraction, and elemental analyses. A 282°C venting chimney from the Bastille edifice was composed primarily of sulfide minerals such as chalcopyrite, marcasite, and sphalerite...
February 2016: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/27587984/erosion-rate-study-at-the-allchar-deposit-macedonia-based-on-radioactive-and-stable-cosmogenic-nuclides-26-al-36-cl-3-he-and-21-ne
#12
M K Pavićević, V Cvetković, S Niedermann, V Pejović, G Amthauer, B Boev, F Bosch, I Aničin, W F Henning
This paper focuses on constraining the erosion rate in the area of the Allchar Sb-As-Tl-Au deposit (Macedonia). It contains the largest known reserves of lorandite (TlAsS2), which is essential for the LORanditeEXperiment (LOREX), aimed at determining the long-term solar neutrino flux. Because the erosion history of the Allchar area is crucial for the success of LOREX, we applied terrestrial in situ cosmogenic nuclides including both radioactive ((26)Al and (36)Cl) and stable ((3)He and (21)Ne) nuclides in quartz, dolomite/calcite, sanidine, and diopside...
February 2016: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/27478414/visualizing-tephra-deposits-and-sedimentary-processes-in-the-marine-environment-the-potential-of-x-ray-microtomography
#13
Adam J Griggs, Siwan M Davies, Peter M Abbott, Mark Coleman, Adrian P Palmer, Tine L Rasmussen, Richard Johnston
Localized tephra deposition in marine sequences is the product of many complex primary and secondary depositional processes. These can significantly influence the potential applicability of tephra deposits as isochronous marker horizons and current techniques, used in isolation, may be insufficient to fully unravel these processes. Here we demonstrate the innovative application of X-ray microtomography (µCT) to successfully identify tephra deposits preserved within marine sediments and use these parameters to reconstruct their internal three-dimensional structure...
December 2015: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/27840594/advantages-of-a-conservative-velocity-interpolation-cvi-scheme-for-particle-in-cell-methods-with-application-in-geodynamic-modeling
#14
Hongliang Wang, Roberto Agrusta, Jeroen van Hunen
The particle-in-cell method is generally considered a flexible and robust method to model the geodynamic problems with chemical heterogeneity. However, velocity interpolation from grid points to particle locations is often performed without considering the divergence of the velocity field, which can lead to significant particle dispersion or clustering if those particles move through regions of strong velocity gradients. This may ultimately result in cells void of particles, which, if left untreated, may, in turn, lead to numerical inaccuracies...
June 2015: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/26709352/abbot-ice-shelf-structure-of-the-amundsen-sea-continental-margin-and-the-southern-boundary-of-the-bellingshausen-plate-seaward-of-west-antarctica
#15
James R Cochran, Kirsty J Tinto, Robin E Bell
Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia...
May 2015: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/27642264/tracking-the-weathering-of-basalts-on-mars-using-lithium-isotope-fractionation-models
#16
Alberto G Fairén, Elisabeth Losa-Adams, Carolina Gil-Lozano, Luis Gago-Duport, Esther R Uceda, Steven W Squyres, J Alexis P Rodríguez, Alfonso F Davila, Christopher P McKay
Lithium (Li), the lightest of the alkali elements, has geochemical properties that include high aqueous solubility (Li is the most fluid mobile element) and high relative abundance in basalt-forming minerals (values ranking between 0.2 and 12 ppm). Li isotopes are particularly subject to fractionation because the two stable isotopes of lithium-(7)Li and (6)Li-have a large relative mass difference (∼15%) that results in significant fractionation between water and solid phases. The extent of Li isotope fractionation during aqueous alteration of basalt depends on the dissolution rate of primary minerals-the source of Li-and on the precipitation kinetics, leading to formation of secondary phases...
April 2015: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/27656114/viscosity-measurements-of-crystallizing-andesite-from-tungurahua-volcano-ecuador
#17
Magdalena Oryaëlle Chevrel, Corrado Cimarelli, Lea deBiasi, Jonathan B Hanson, Yan Lavallée, Fabio Arzilli, Donald B Dingwell
Viscosity has been determined during isothermal crystallization of an andesite from Tungurahua volcano (Ecuador). Viscosity was continuously recorded using the concentric cylinder method and employing a Pt-sheathed alumina spindle at 1 bar and from 1400°C to subliquidus temperatures to track rheological changes during crystallization. The disposable spindle was not extracted from the sample but rather left in the sample during quenching thus preserving an undisturbed textural configuration of the crystals...
March 2015: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/26693211/grain-size-dynamics-beneath-mid-ocean-ridges-implications-for-permeability-and-melt-extraction
#18
Andrew J Turner, Richard F Katz, Mark D Behn
Grain size is an important control on mantle viscosity and permeability, but is difficult or impossible to measure in situ. We construct a two-dimensional, single phase model for the steady state mean grain size beneath a mid-ocean ridge. The mantle rheology is modeled as a composite of diffusion creep, dislocation creep, dislocation accommodated grain boundary sliding, and a plastic stress limiter. The mean grain size is calculated by the paleowattmeter relationship of Austin and Evans (2007). We investigate the sensitivity of our model to global variations in grain growth exponent, potential temperature, spreading-rate, and mantle hydration...
March 2015: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/26321881/deep-water-recycling-through-time
#19
Valentina Magni, Pierre Bouilhol, Jeroen van Hunen
We investigate the dehydration processes in subduction zones and their implications for the water cycle throughout Earth's history. We use a numerical tool that combines thermo-mechanical models with a thermodynamic database to examine slab dehydration for present-day and early Earth settings and its consequences for the deep water recycling. We investigate the reactions responsible for releasing water from the crust and the hydrated lithospheric mantle and how they change with subduction velocity (vs ), slab age (a) and mantle temperature (Tm)...
November 2014: Geochemistry, Geophysics, Geosystems: G³
https://www.readbyqxmd.com/read/26300699/paleomagnetic-recording-fidelity-of-nonideal-magnetic-systems
#20
Adrian R Muxworthy, David Krása, Wyn Williams, Trevor P Almeida
A suite of near-identical magnetite nanodot samples produced by electron-beam lithography have been used to test the thermomagnetic recording fidelity of particles in the 74-333 nm size range; the grain size range most commonly found in rocks. In addition to controlled grain size, the samples had identical particle spacings, meaning that intergrain magnetostatic interactions could be controlled. Their magnetic hysteresis parameters were indicative of particles thought not to be ideal magnetic recorders; however, the samples were found to be excellent thermomagnetic recorders of the magnetic field direction...
June 2014: Geochemistry, Geophysics, Geosystems: G³
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