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Geochemistry, Geophysics, Geosystems: G³

Édouard G H Philippe, Jean-Pierre Valet, Guillaume St-Onge, Anojh Thevarasan
Sampling of sediment cores using plastic U-channels has made possible the acquisition of detailed records of paleomagnetic secular variation, geomagnetic polarity, environmental magnetic studies, and relative paleointensity over the past several million years. U-channel measurements provide the great advantage of rapid measurements of long sediment cores, but the signal resolution is attenuated by the response function of the magnetometer sensors, which therefore restrains the recovery of rapid and large-amplitude field changes...
November 2018: Geochemistry, Geophysics, Geosystems: G³
Aude Lavayssière, Catherine Rychert, Nicholas Harmon, Derek Keir, James O S Hammond, J-Michael Kendall, Cécile Doubre, Sylvie Leroy
Imaging the lithosphere is key to understand mechanisms of extension as rifting progresses. Continental rifting results in a combination of mechanical stretching and thinning of the lithosphere, decompression upwelling, heating, sometimes partial melting of the asthenosphere, and potentially partial melting of the mantle lithosphere. The northern East African Rift system is an ideal locale to study these processes as it exposes the transition from tectonically active continental rifting to incipient seafloor spreading...
October 2018: Geochemistry, Geophysics, Geosystems: G³
Jennifer Brandstätter, Walter Kurz, Sylvain Richoz, Matthew J Cooper, Damon A H Teagle
Carbonate veins in the igneous basement and in the lithified sedimentary cover of the Cocos Ridge at International Ocean Discovery Program (IODP) Hole 344-U1414A reveal the hydrologic system and fluid-rock interactions. IODP Hole 344-U1414A was drilled on the northern flank of the Cocos Ridge and is situated 1 km seaward from the Middle America Trench offshore Costa Rica. Isotopic and elemental compositions were analyzed to constrain the fluid source of the carbonate veins and to reveal the thermal history of Hole 344-U1414A...
October 2018: Geochemistry, Geophysics, Geosystems: G³
Stefano M Bernasconi, Inigo A Müller, Kristin D Bergmann, Sebastian F M Breitenbach, Alvaro Fernandez, David A Hodell, Madalina Jaggi, Anna Nele Meckler, Isabel Millan, Martin Ziegler
About a decade after its introduction, the field of carbonate clumped isotope thermometry is rapidly expanding because of the large number of possible applications and its potential to solve long-standing questions in Earth Sciences. Major factors limiting the application of this method are the very high analytical precision required for meaningful interpretations, the relatively complex sample preparation procedures, and the mass spectrometric corrections needed. In this paper we first briefly review the evolution of the analytical and standardization procedures and discuss the major remaining sources of uncertainty...
September 2018: Geochemistry, Geophysics, Geosystems: G³
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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