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A Geyer, A M Álvarez-Valero, G Gisbert, M Aulinas, D Hernández-Barreña, A Lobo, J Marti
Deception Island (South Shetland Islands) is one of the most active volcanoes in Antarctica, with more than 20 explosive eruptive events registered over the past two centuries. Recent eruptions (1967, 1969, and 1970) and the volcanic unrest episodes that happened in 1992, 1999, and 2014-2015 demonstrate that the occurrence of future volcanic activity is a valid and pressing concern for scientists, technical and logistic personnel, and tourists, that are visiting or working on or near the island. We present a unifying evolutionary model of the magmatic system beneath Deception Island by integrating new petrologic and geochemical results with an exhaustive database of previous studies in the region...
January 23, 2019: Scientific Reports
Charline Lormand, Georg F Zellmer, Károly Németh, Geoff Kilgour, Stuart Mead, Alan S Palmer, Naoya Sakamoto, Hisayoshi Yurimoto, Anja Moebis
Crystals within volcanic rocks record geochemical and textural signatures during magmatic evolution before eruption. Clues to this magmatic history can be examined using crystal size distribution (CSD) studies. The analysis of CSDs is a standard petrological tool, but laborious due to manual hand-drawing of crystal margins. The trainable Weka segmentation (TWS) plugin in ImageJ is a promising alternative. It uses machine learning and image segmentation to classify an image. We recorded back-scattered electron (BSE) images of three volcanic samples with different crystallinity (35, 50 and ≥85 vol...
December 2018: Microscopy and Microanalysis
Uwe Jenchen
From samples of the Middle to Late Triassic El Tranquilo Group (El Tranquilo anticline, Deseado Massif, Patagonia) petrographic (qualitative and modal) analyses and geochemical analyses (major, trace elements, and rare earth elements (REEs)) of 80 samples were carried out. The data presented here contain a broad overview of photomicrography, recalculated modal point-count data, geochemical raw data, and simple statistics of selected geochemical parameters. The data presented in this article are interpreted and discussed in the research article entitled "Petrography and geochemistry of the Triassic El Tranquilo Group, Deseado Massif, Patagonia, Argentina: Implications for provenance and tectonic setting" (Jenchen, 2018)...
December 2018: Data in Brief
Artur Benisek, Edgar Dachs
The internal energies and entropies of 21 well-known minerals were calculated using the density functional theory (DFT), viz. kyanite, sillimanite, andalusite, albite, microcline, forsterite, fayalite, diopside, jadeite, hedenbergite, pyrope, grossular, talc, pyrophyllite, phlogopite, annite, muscovite, brucite, portlandite, tremolite, and CaTiO3 -perovskite. These thermodynamic quantities were then transformed into standard enthalpies of formation from the elements and standard entropies enabling a direct comparison with tabulated values...
2018: Contributions to Mineralogy and Petrology. Beiträge Zur Mineralogie und Petrologie
Anthony I S Kemp
Many studies link the presence of continents on Earth to the operation of plate tectonics. Radiogenic isotope data have, however, long consigned the bulk of crust generation and preservation to the murky realm of the Precambrian Earth, where the prevailing geodynamic systems are highly uncertain due to the sparse and complex nature of the geological record of these early eons. The purpose of this paper is to examine the nature of this geological record, considering the biases and artefacts that may undermine its fidelity, and to assess what are the most robust lines of evidence from which meaningful geodynamic inferences can be drawn...
October 1, 2018: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
S Widiyantoro, M Ramdhan, J-P Métaxian, P R Cummins, C Martel, S Erdmann, A D Nugraha, A Budi-Santoso, A Laurin, A A Fahmi
Our seismic tomographic images characterize, for the first time, spatial and volumetric details of the subvertical magma plumbing system of Merapi Volcano. We present P- and S-wave arrival time data, which were collected in a dense seismic network, known as DOMERAPI, installed around the volcano for 18 months. The P- and S-wave arrival time data with similar path coverage reveal a high Vp/Vs structure extending from a depth of ≥20 km below mean sea level (MSL) up to the summit of the volcano. Combined with results of petrological studies, our seismic tomography data allow us to propose: (1) the existence of a shallow zone of intense fluid percolation, directly below the summit of the volcano; (2) a main, pre-eruptive magma reservoir at ≥ 10 to 20 km below MSL that is orders of magnitude larger than erupted magma volumes; (3) a deep magma reservoir at MOHO depth which supplies the main reservoir; and (4) an extensive, subvertical fluid-magma-transfer zone from the mantle to the surface...
September 12, 2018: Scientific Reports
Matthew S Tarling, Steven A F Smith, Cecilia Viti, James M Scott
Laboratory experiments on serpentinite suggest that extreme dynamic weakening at earthquake slip rates is accompanied by amorphisation, dehydration and possible melting. However, hypotheses arising from experiments remain untested in nature, because earthquake ruptures have not previously been recognised in serpentinite shear zones. Here we document the progressive formation of high-temperature reaction products that formed by coseismic amorphisation and dehydration in a plate boundary-scale serpentinite shear zone...
September 3, 2018: Nature Communications
Carl A Peters, Simon C George
Research on the early rise of oxygenic photosynthesis and eukaryotes has recently encountered a major pitfall, as some hopane and sterane biomarkers reported in Archaean rocks are the results of contamination. Following an extensive petrological framework in the Pilbara Craton, Western Australia, oil-bearing fluid inclusions and solid bitumens were identified in replacement and hydrothermal carbonate veins cross-cutting Archaean metasedimentary rocks. The 2.55-2.63 billion years old metasedimentary rocks were found to be depleted of indigenous biomarkers...
November 2018: Geobiology
Sara Di Salvo, Eleonora Braschi, Martina Casalini, Sara Marchionni, Teresa Adani, Maurizio Ulivi, Andrea Orlando, Simone Tommasini, Riccardo Avanzinelli, Paul P A Mazza, Sandro Conticelli, Lorella Francalanci
An analytical protocol for high-precision, in situ microscale isotopic investigations is presented here, which combines the use of a high-performing mechanical microsampling device and high-precision TIMS measurements on micro-Sr samples, allowing for excellent results both in accuracy and precision. The present paper is a detailed methodological description of the whole analytical procedure from sampling to elemental purification and Sr-isotope measurements. The method offers the potential to attain isotope data at the microscale on a wide range of solid materials with the use of minimally invasive sampling...
2018: Journal of Analytical Methods in Chemistry
Liang Yue, ZiLiang Liu, Yongsheng Ma
The Precambrian sedimentary strata on the southern margin of the North China Craton are well developed and widely exposed, making the region ideal for the study of depositional processes. However, because of the length of the depositional history and the lack of biogenic criteria, interpretations of the sedimentary environments of the Precambrian strata are often based on the tectonic background, geographical environment, rock type and sedimentary structures, resulting in controversies in the literature. In this study of the Bingmagou Formation in the Ruyang Group on the southern margin of the North China Craton, analysis of petrologic features, palaeocurrents and sedimentary facies is combined with regional correlation of relevant strata and the reconstruction of ancient landforms to explain the depositional environments and environmental transitions...
May 29, 2018: Scientific Reports
M Fedi, F Cella, M D'Antonio, G Florio, V Paoletti, V Morra
We analyze a wide gravity low in the Campania Active Volcanic Area and interpret it by a large and deep source distribution of partially molten, low-density material from about 8 to 30 km depth. Given the complex spatial-temporal distribution of explosive volcanism in the area, we model the gravity data consistently with several volcanological and petrological constraints. We propose two possible models: one accounts for the coexistence, within the lower/intermediate crust, of large amounts of melts and cumulates besides country rocks...
May 29, 2018: Scientific Reports
Erell Leocat, Christophe Rielland, Patrice Letessier
The issue of Elongated Mineral Particles (EMP) in building materials has been revealed during roadworks in 2013 in France. In fact, road coating aggregates are made of specific rock gravels that can contain Naturally Occurring Asbestos (NOA), which is mainly actinolite. The legislation refers to six regulatory asbestos, that consist in asbestiform habitus of the six minerals. The current technical standard is not adapted for analyzing natural material, as it cannot distinguish the asbestiform fibers and the cleavage fragments fibers...
May 3, 2018: Toxicology and Applied Pharmacology
Larry R Nittler, Conel M O'D Alexander, Jemma Davidson, My E I Riebe, Rhonda M Stroud, Jianhua Wang
NanoSIMS C-, N-, and O-isotopic mapping of matrix in CO3.0 chondrite Dominion Range (DOM) 08006 revealed it to have in its matrix the highest abundance of presolar O-rich grains (257 +76/-96 ppm, 2σ) of any meteorite. It also has a matrix abundance of presolar SiC of 35 (+25/-17, 2σ) ppm, similar to that seen across primitive chondrite classes. This provides additional support to bulk isotopic and petrologic evidence that DOM 08006 is the most primitive known CO meteorite. Transmission electron microscopy of five presolar silicate grains revealed one to have a composite mineralogy similar to larger amoeboid olivine aggregates and consistent with equilibrium condensation, two non-stoichiometric amorphous grains and two olivine grains, though one is identified as such solely based on its composition...
April 1, 2018: Geochimica et Cosmochimica Acta
Chunquan Yu, Elizabeth A Day, Maarten V de Hoop, Michel Campillo, Saskia Goes, Rachel A Blythe, Robert D van der Hilst
Global seismic discontinuities near 410 and 660 km depth in Earth's mantle are expressions of solid-state phase transitions. These transitions modulate thermal and material fluxes across the mantle and variations in their depth are often attributed to temperature anomalies. Here we use novel seismic array analysis of SS waves reflecting off the 410 and 660 below the Hawaiian hotspot. We find amplitude-distance trends in reflectivity that imply lateral variations in wavespeed and density contrasts across 660 for which thermodynamic modeling precludes a thermal origin...
March 28, 2018: Nature Communications
David McDougal, Daisuke Nakashima, Travis J Tenner, Noriko T Kita, John W Valley, Takaaki Noguchi
High precision oxygen three-isotope ratios were measured for four mineral phases (olivine, low-Ca and high-Ca pyroxene, and plagioclase) in equilibrated ordinary chondrites (EOC) using a secondary ion mass spectrometer. Eleven EOCs were studied that cover all groups (H, L, LL) and petrologic types (4, 5, 6), including S1-S4 shock stages, as well as unbrecciated and brecciated meteorites. SIMS analyses of multiple minerals were made in close proximity (mostly <100 μm) from several areas in each meteorite thin section, to evaluate isotope exchange among minerals...
November 2017: Meteoritics & Planetary Science
Chad L Yost, Lily J Jackson, Jeffery R Stone, Andrew S Cohen
The temporal proximity of the ∼74 ka Toba supereruption to a putative 100-50 ka human population bottleneck is the basis for the volcanic winter/weak Garden of Eden hypothesis, which states that the eruption caused a 6-year-long global volcanic winter and reduced the effective population of anatomically modern humans (AMH) to fewer than 10,000 individuals. To test this hypothesis, we sampled two cores collected from Lake Malawi with cryptotephra previously fingerprinted to the Toba supereruption. Phytolith and charcoal samples were continuously collected at ∼3-4 mm (∼8-9 yr) intervals above and below the Toba cryptotephra position, with no stratigraphic breaks...
March 2018: Journal of Human Evolution
Francesca Di Luccio, Giovanni Chiodini, Stefano Caliro, Carlo Cardellini, Vincenzo Convertito, Nicola Alessandro Pino, Cristiano Tolomei, Guido Ventura
Intrusions are a ubiquitous component of mountain chains and testify to the emplacement of magma at depth. Understanding the emplacement and growth mechanisms of intrusions, such as diapiric or dike-like ascent, is critical to constrain the evolution and structure of the crust. Petrological and geological data allow us to reconstruct magma pathways and long-term magma differentiation and assembly processes. However, our ability to detect and reconstruct the short-term dynamics related to active intrusive episodes in mountain chains is embryonic, lacking recognized geophysical signals...
January 2018: Science Advances
Patricia L Clay, Ray Burgess, Henner Busemann, Lorraine Ruzié-Hamilton, Bastian Joachim, James M D Day, Christopher J Ballentine
Volatile element delivery and retention played a fundamental part in Earth's formation and subsequent chemical differentiation. The heavy halogens-chlorine (Cl), bromine (Br) and iodine (I)-are key tracers of accretionary processes owing to their high volatility and incompatibility, but have low abundances in most geological and planetary materials. However, noble gas proxy isotopes produced during neutron irradiation provide a high-sensitivity tool for the determination of heavy halogen abundances. Using such isotopes, here we show that Cl, Br and I abundances in carbonaceous, enstatite, Rumuruti and primitive ordinary chondrites are about 6 times, 9 times and 15-37 times lower, respectively, than previously reported and usually accepted estimates...
November 29, 2017: Nature
Oğuz H Göğüş, Russell N Pysklywec, A M C Şengör, Erkan Gün
Lithospheric drips have been interpreted for various regions around the globe to account for the recycling of the continental lithosphere and rapid plateau uplift. However, the validity of such hypothesis is not well documented in the context of geological, geophysical and petrological observations that are tested against geodynamical models. Here we propose that the folding of the Central Anatolian (Kırşehir) arc led to thickening of the lithosphere and onset of "dripping" of the arc root. Our geodynamic model explains the seismic data showing missing lithosphere and a remnant structure characteristic of a dripping arc root, as well as enigmatic >1 km uplift over the entire plateau, Cappadocia and Galatia volcanism at the southern and northern plateau margins since ~10 Ma, respectively...
November 16, 2017: Nature Communications
Clément Ganino, Guy Libourel
Early Solar System planetesimal thermal models predict the heating of the chondritic protolith and the preservation of a chondritic crust on differentiated parent bodies. Petrological and geochemical analyses of chondrites have suggested that secondary alteration phases formed at low temperatures (<300 °C) by fluid-rock interaction where reduced and oxidized Vigarano type Carbonaceous (CV) chondrites witness different physicochemical conditions. From a thermodynamical survey of Ca-Fe-rich secondary phases in CV3 chondrites including silica activity (aSiO2 ), here we show that the classical distinction between reduced and oxidized chondrites is no longer valid and that their Ca-Fe-rich secondary phases formed in similar reduced conditions near the iron-magnetite redox buffer at low aSiO2 (log(aSiO2 ) <-1) and moderate temperature (210-610 °C)...
August 15, 2017: Nature Communications
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