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https://www.readbyqxmd.com/read/29974603/hydrocarbon-biomarkers-preserved-in-carbonate-veins-of-potentially-paleoproterozoic-age-and-implications-for-the-early-biosphere
#1
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...
July 5, 2018: Geobiology
https://www.readbyqxmd.com/read/29850369/high-precision-in-situ-87-sr-86-sr-analyses-through-microsampling-on-solid-samples-applications-to-earth-and-life-sciences
#2
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
https://www.readbyqxmd.com/read/29844488/sedimentary-environment-and-depositional-evolution-of-the-mesoproterozoic-bingmagou-formation-on-the-southern-margin-of-the-north-china-craton
#3
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
https://www.readbyqxmd.com/read/29844430/gravity-modeling-finds-a-large-magma-body-in-the-deep-crust-below-the-gulf-of-naples-italy
#4
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
https://www.readbyqxmd.com/read/29730310/analysis-and-identification-of-elongated-mineral-particles-in-road-coated-aggregates
#5
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
https://www.readbyqxmd.com/read/29628527/high-abundances-of-presolar-grains-and-15-n-rich-organic-matter-in-co3-0-chondrite-dominion-range-08006
#6
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
https://www.readbyqxmd.com/read/29593266/compositional-heterogeneity-near-the-base-of-the-mantle-transition-zone-beneath-hawaii
#7
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
https://www.readbyqxmd.com/read/29551884/intermineral-oxygen-three-isotope-systematics-of-silicate-minerals-in-equilibrated-ordinary-chondrites
#8
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
https://www.readbyqxmd.com/read/29477183/subdecadal-phytolith-and-charcoal-records-from-lake-malawi-east-africa-imply-minimal-effects-on-human-evolution-from-the-%C3%A2-74-ka-toba-supereruption
#9
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
https://www.readbyqxmd.com/read/29326978/seismic-signature-of-active-intrusions-in-mountain-chains
#10
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
https://www.readbyqxmd.com/read/29189777/halogens-in-chondritic-meteorites-and-terrestrial-accretion
#11
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
https://www.readbyqxmd.com/read/29142259/drip-tectonics-and-the-enigmatic-uplift-of-the-central-anatolian-plateau
#12
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
https://www.readbyqxmd.com/read/28811478/reduced-and-unstratified-crust-in-cv-chondrite-parent-body
#13
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
https://www.readbyqxmd.com/read/28724931/assessing-the-shock-state-of-the-lunar-highlands-implications-for-the-petrogenesis-and-chronology-of-crustal-anorthosites
#14
J F Pernet-Fisher, K H Joy, D J P Martin, K L Donaldson Hanna
Our understanding of the formation and evolution of the primary lunar crust is based on geochemical systematics from the lunar ferroan anorthosite (FAN) suite. Recently, much effort has been made to understand this suite's petrologic history to constrain the timing of crystallisation and to interpret FAN chemical diversity. We investigate the shock histories of lunar anorthosites by combining Optical Microscope (OM) 'cold' cathodoluminescence (CL)-imaging and Fourier Transform Infrared (FTIR) spectroscopy analyses...
July 19, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28489866/magmatic-evolution-of-panama-canal-volcanic-rocks-a-record-of-arc-processes-and-tectonic-change
#15
David W Farris, Agustin Cardona, Camilo Montes, David Foster, Carlos Jaramillo
Volcanic rocks along the Panama Canal present a world-class opportunity to examine the relationship between arc magmatism, tectonic forcing, wet and dry magmas, and volcanic structures. Major and trace element geochemistry of Canal volcanic rocks indicate a significant petrologic transition at 21-25 Ma. Oligocene Bas Obispo Fm. rocks have large negative Nb-Ta anomalies, low HREE, fluid mobile element enrichments, a THI of 0.88, and a H2Ocalc of >3 wt. %. In contrast, the Miocene Pedro Miguel and Late Basalt Fm...
2017: PloS One
https://www.readbyqxmd.com/read/28295045/stochastic-modelling-of-deep-magmatic-controls-on-porphyry-copper-deposit-endowment
#16
Massimo Chiaradia, Luca Caricchi
Porphyry deposits, our main source of copper and of significant amounts of Mo, Re and Au, form at convergent margins in association with intermediate-felsic magmas. Although it is accepted that copper is transported and precipitated by fluids released by these magmas, the magmatic processes leading to the formation of economic deposits remain elusive. Here we perform Monte Carlo petrological and geochemical modelling to quantitatively link crustal magmatic processes and the geochemical signatures of magmas (i...
March 15, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28264194/rheological-separation-of-the-megathrust-seismogenic-zone-and-episodic-tremor-and-slip
#17
Xiang Gao, Kelin Wang
Episodic tremor and accompanying slow slip, together called ETS, is most often observed in subduction zones of young and warm subducting slabs. ETS should help us to understand the mechanics of subduction megathrusts, but its mechanism is still unclear. It is commonly assumed that ETS represents a transition from seismic to aseismic behaviour of the megathrust with increasing depth, but this assumption is in contradiction with an observed spatial separation between the seismogenic zone and the ETS zone. Here we propose a unifying model for the necessary geological condition of ETS that explains the relationship between the two zones...
March 16, 2017: Nature
https://www.readbyqxmd.com/read/28261660/fragmentation-of-wall-rock-garnets-during-deep-crustal-earthquakes
#18
Håkon Austrheim, Kristina G Dunkel, Oliver Plümper, Benoit Ildefonse, Yang Liu, Bjørn Jamtveit
Fractures and faults riddle the Earth's crust on all scales, and the deformation associated with them is presumed to have had significant effects on its petrological and structural evolution. However, despite the abundance of directly observable earthquake activity, unequivocal evidence for seismic slip rates along ancient faults is rare and usually related to frictional melting and the formation of pseudotachylites. We report novel microstructures from garnet crystals in the immediate vicinity of seismic slip planes that transected lower crustal granulites during intermediate-depth earthquakes in the Bergen Arcs area, western Norway, some 420 million years ago...
February 2017: Science Advances
https://www.readbyqxmd.com/read/28242686/previously-unknown-class-of-metalorganic-compounds-revealed-in-meteorites
#19
Alexander Ruf, Basem Kanawati, Norbert Hertkorn, Qing-Zhu Yin, Franco Moritz, Mourad Harir, Marianna Lucio, Bernhard Michalke, Joshua Wimpenny, Svetlana Shilobreeva, Basil Bronsky, Vladimir Saraykin, Zelimir Gabelica, Régis D Gougeon, Eric Quirico, Stefan Ralew, Tomasz Jakubowski, Henning Haack, Michael Gonsior, Peter Jenniskens, Nancy W Hinman, Philippe Schmitt-Kopplin
The rich diversity and complexity of organic matter found in meteorites is rapidly expanding our knowledge and understanding of extreme environments from which the early solar system emerged and evolved. Here, we report the discovery of a hitherto unknown chemical class, dihydroxymagnesium carboxylates [(OH)2 MgO2 CR]- , in meteoritic soluble organic matter. High collision energies, which are required for fragmentation, suggest substantial thermal stability of these Mg-metalorganics (CHOMg compounds). This was corroborated by their higher abundance in thermally processed meteorites...
March 14, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28223715/massive-production-of-abiotic-methane-during-subduction-evidenced-in-metamorphosed-ophicarbonates-from-the-italian-alps
#20
Alberto Vitale Brovarone, Isabelle Martinez, Agnès Elmaleh, Roberto Compagnoni, Carine Chaduteau, Cristiano Ferraris, Imène Esteve
Alteration of ultramafic rocks plays a major role in the production of hydrocarbons and organic compounds via abiotic processes on Earth and beyond and contributes to the redistribution of C between solid and fluid reservoirs over geological cycles. Abiotic methanogenesis in ultramafic rocks is well documented at shallow conditions, whereas natural evidence at greater depths is scarce. Here we provide evidence for intense high-pressure abiotic methanogenesis by reduction of subducted ophicarbonates. Protracted (≥0...
February 22, 2017: Nature Communications
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