Organic Geochemistry of Earth's Upper Mantle Fluids

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Geothermometric Constraints on the Thermal Architecture, Metamorphism, and Exhumation of the Northern Range, Trinidad

The Northern Range of Trinidad is composed of Mesozoic passive margin sedimentary rocks that underwent ductile deformation and subgreenschist- to greenschist-facies metamorphism in the early Miocene. Previous studies suggested a two-stage formation of the Northern Range between the Caribbean and South American plates: an initial collision drove mountain building in the Miocene and subsequent strike-slip plate motion preferentially exhumed the western segment, producing a westward increase in the metamorphic thermal gradient. However, these studies were not able to resolve whether this gradient was discrete or continuous so the tectonic model awaits testing. In this study we use Raman spectroscopy on carbonaceous material (RSCM), an empirical geothermometer, to constrain peak temperatures across the Northern Range with a greater resolution than was available in previous studies. The RSCM temperatures show an abrupt increase from 337°C ± 10°C in the east to 442°C ± 16°C west of Chupara Point, where a range-cutting fault (Chupara Fault) had been inferred in previous geologic mapping campaigns. Thus, the discrete thermal discontinuity of ~100°C very likely represents the Chupara Fault. Our RSCM-derived peak metamorphic temperatures are 50°C to 100°C higher than those from previous estimates, requiring revision of tectonic models to account for deeper burial and greater exhumation. The peak metamorphic conditions determined here, and the deduced timing of faulting from published thermochronological data, are consistent with the two-stage tectonic model proposed in previous studies

Field‐based evidence for intra‐slab high‐permeability channel formation at eclogite‐facies conditions during subduction

International audienceFluid release from subducting oceanic lithosphere is a key process for subduction zone geodynamics, from controlling arc volcanism to seismicity and tectonic exhumation. However, many fundamental details of fluid composition, flow pathways, and reactivity with slab-forming rocks remain to be thoroughly understood. In this study we investigate a multi-kilometer-long, high-pressure metasomatic system preserved in the lawsonite-eclogite metamorphic unit of Alpine Corsica, France. The fluid-mediated process was localized along a major intra-slab interface, which is the contact between basement and cover unit. Two distinct metasomatic stages are identified and discussed. We show that these two stages resulted from the infiltration of deep fluids that were derived from the same source and had the same slab-parallel, updip flow direction. By mass balance analysis, we quantify metasomatic mass changes along this fluid pathway and the time-integrated fluid fluxes responsible for them. In addition, we also assess carbon fluxes associated with these metasomatic events. The magnitude of the estimated fluid fluxes (104-105) indicates that major intra-slab interfaces such as lithological boundaries acted as fluid channels facilitating episodic pulses of fluid flow. We also show that when fluids are channelized, high time-integrated fluid fluxes lead to carbon fluxes several orders of magnitude higher than carbon fluxes generated by local dehydration reactions. Given the size and geologic features of the investigated metasomatic system, we propose that it represents the first reported natural analogue of the so-called high permeability channels predicted by numerical simulations

Bone structural similarity score: a multiparametric tool to match properties of biomimetic bone substitutes with their target tissues

Background: One of the hardest tasks in developing or selecting grafts for bone substitution surgery or tissue engineering is to match the structural and mechanical properties of tissue at the recipient site, because of the large variability of tissue properties with anatomical site, sex, age and health conditions of the patient undergoing implantation. We investigated the feasibility of defining a quantitative bone structural similarity score based on differences in the structural properties of synthetic grafts and bone tissue. Methods: Two biocompatible hydroxyapatite porous scaffolds with different nominal pore sizes were compared with trabecular bone tissues from equine humerus and femur. Images of samples’ structures were acquired by high-resolution micro-computed tomography and analyzed to estimate porosity, pore size distribution and interconnectivity, specific surface area, connectivity density and degree of anisotropy. Young’s modulus and stress at break were measured by compression tests. Structural similarity distances between sample pairs were defined based on scaled and weighted differences of the measured properties. Their feasibility was investigated for scoring structural similarity between considered scaffolds or bone tissues. Results: Manhattan distances and Quadrance generally showed sound and consistent similarities between sample pairs, more clearly than simple statistical comparison and with discriminating capacity similar to image-based scores to assess progression of pathologies affecting bone structure. Conclusions: The results suggest that a quantitative and objective bone structural similarity score may be defined to help biomaterials scientists fabricate, and surgeons select, the graft or scaffold best mimicking the structure of a given bone tissue

Hydrogenation reactions of carbon on Earth: linking methane, margarine, and life

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in McGlynn, S. E., Glass, J. B., Johnson-Finn, K., Klein, F., Sanden, S. A., Schrenk, M. O., Ueno, Y., & Vitale-Brovarone, A. Hydrogenation reactions of carbon on Earth: linking methane, margarine, and life. American Mineralogist, 105(5), (2020): 599-608, doi:10.2138/am-2020-6928CCBYNCND.Hydrogenation reactions are a major route of electron and proton flow on Earth. Interfacing geology and organic chemistry, hydrogenations occupy pivotal points in the Earth’s global geochemical cycles. Some examples of hydrogenation reactions on Earth today include the production and consumption of methane in both abiotic and biotic reactions, the reduction of protons in hydrothermal settings, and the biological synthesis and degradation of fatty acids. Hydrogenation reactions were likely important for prebiotic chemistry on the early Earth, and today serve as one of the fundamental reaction classes that enable cellular life to construct biomolecules. An understanding and awareness of hydrogenation reactions is helpful for comprehending the larger web of molecular and material inter-conversions on our planet. In this brief review we detail some important hydrogenation and dehydrogenation reactions as they relate to geology, biology, industry, and atmospheric chemistry. Such reactions have implications ranging from the suite of reactions on early Earth to industrial applications like the production of hydrocarbon fuel.S.E.M. is supported by NSF Award 1724300 and JSPS KAKENHI Grant JP18H01325. A.V.B. is supported by ANR T-ERC, CNRS INSU-SYSTER, and Rita Levi Montalcini by MIUR. J.B.G. is supported by NASA Exobiology Grant NNX14AJ87G and 80NSSC19K0477. F.K. is supported by NSF-OCE award 1634032 and 1427274. M.O.S. is supported by the NASA Astrobiology Institute Rock-Powered Life Grant NNA15BB02A

Deep Earth carbon reactions through time and space

The authors acknowledge partial support from the Sloan Foundation grant G-2016-7157.Reactions involving carbon in the deep Earth have limited manifestation on Earth’s surface, yet they have played a critical role in the evolution of our planet. The metal-silicate partitioning reaction promoted carbon capture during Earth’s accretion and may have sequestered substantial carbon in Earth’s core. The freezing reaction involving iron-carbon liquid could have contributed to the growth of Earth’s inner core and the geodynamo. The redox melting/freezing reaction largely controls the movement of carbon in the modern mantle, and reactions between carbonates and silicates in the deep mantle also promote carbon mobility. The ten-year activity of the Deep Carbon Observatory has made important contributions to our knowledge of how these reactions are involved in the cycling of carbon throughout our planet, both past and present, and helped to identify gaps in our understanding that motivate and give direction to future studies.Publisher PDFPeer reviewe

Coupled surface to deep Earth processes: Perspectives from TOPO-EUROPE with an emphasis on climate- and energy-related societal challenges

Understanding the interactions between surface and deep Earth processes is important for research in many diverse scientific areas including climate, environment, energy, georesources and biosphere. The TOPO-EUROPE initiative of the International Lithosphere Program serves as a pan-European platform for integrated surface and deep Earth sciences, synergizing observational studies of the Earth structure and fluxes on all spatial and temporal scales with modelling of Earth processes. This review provides a survey of scientific developments in our quantitative understanding of coupled surface-deep Earth processes achieved through TOPO-EUROPE. The most notable innovations include (1) a process-based understanding of the connection of upper mantle dynamics and absolute plate motion frames; (2) integrated models for sediment source-to-sink dynamics, demonstrating the importance of mass transfer from mountains to basins and from basin to basin; (3) demonstration of the key role of polyphase evolution of sedimentary basins, the impact of pre-rift and pre-orogenic structures, and the evolution of subsequent lithosphere and landscape dynamics; (4) improved conceptual understanding of the temporal evolution from back-arc extension to tectonic inversion and onset of subduction; (5) models to explain the integrated strength of Europe's lithosphere; (6) concepts governing the interplay between thermal upper mantle processes and stress-induced intraplate deformation; (7) constraints on the record of vertical motions from high-resolution data sets obtained from geo-thermochronology for Europe's topographic evolution; (8) recognition and quantifications of the forcing by erosional and/or glacial-interglacial surface mass transfer on the regional magmatism, with major implications for our understanding of the carbon cycle on geological timescales and the emerging field of biogeodynamics; and (9) the transfer of insights obtained on the coupling of deep Earth and surface processes to the domain of geothermal energy exploration. Concerning the future research agenda of TOPO-EUROPE, we also discuss the rich potential for further advances, multidisciplinary research and community building across many scientific frontiers, including research on the biosphere, climate and energy. These will focus on obtaining a better insight into the initiation and evolution of subduction systems, the role of mantle plumes in continental rifting and (super)continent break-up, and the deformation and tectonic reactivation of cratons; the interaction between geodynamic, surface and climate processes, such as interactions between glaciation, sea level change and deep Earth processes; the sensitivity, tipping points, and spatio-temporal evolution of the interactions between climate and tectonics as well as the role of rock melting and outgassing in affecting such interactions; the emerging field of biogeodynamics, that is the impact of coupled deep Earth – surface processes on the evolution of life on Earth; and tightening the connection between societal challenges regarding renewable georesources, climate change, natural geohazards, and novel process-understanding of the Earth system

Impact des structures héritées de l'ouverture océanique mésozoique sur l'évolution tectono-métamorphique Alpine des unités de Haute-Pression en Corse pendant la subduction continentale

La Corse Alpine offre une section complète du prisme orogénique alpin où la plupart des équivalents des unités décrites dans les Alpes Occidentales peuvent être trouvés sur une section de 40 km. Les minéraux d'haute pression sont exceptionnellement bien préservés, particulièrement la lawsonite, offrant un accès unique à la compréhension de zones de subduction. La Corse alpine est formée par une pile complexe d’unités métamorphiques d'origine continentale et océanique. Ces unités ont été interprétées soit comme des mélanges tectoniques complexes formés pendant la subduction alpine, soit comme les parties plus continues de lithosphère continentale et-ou océanique. Les rares estimations de condition PT sur des larges régions de la chaîne résultent en plusieurs incertitudes dans l'identification des limites séparant les unités qui ont subi des évolutions tectono-métamorphiques différentes et, par conséquent, dans la définition d'une architecture complète de la chaîne. Les données de terrain, structurelles et métamorphiques obtenues dans cette étude aux différentes échelles suggèrent que la chaîne de la Corse alpine est caractérisée par une forte conservation de structures pré-alpin, de la micro-échelle à l'échelle de la chaîne, malgré la déformation intense associée avec le métamorphisme, qui a localement donné les conditions du facies éclogitique et lawsonite. En détail, seulement neuf domaines tectono-métamorphiques homogènes ont été identifiés. Ces terrains peuvent être attribué aux domaines paléogéographiques différents qui ont subi des évolutions tectono-métamorphiques différentes. Malgré ça, les données géochronologiques fournies pendant cette étude indiquent que la Corse alpine résulte d'une évolution complexe, étant caractérisée par la signature claire tant de la tectonique alpine Eocène, à 35 Ma, que de la tectonique apennine, à 25 Ma. Les résultats fournis dans cette thèse contribuent non seulement à la compréhension des processus de subduction et de formation de montagnes, mais donnent aussi des contraintes importantes pour déchiffrer les systèmes Tethys-Alpes et Alpes-Apennine.Alpine Corsica offers a complete section through the Alpine orogenic wedge where most equivalent of the units described in the Western Alps may be found over a 40 km section. High-pressure mineral assemblages are exceptionally well preserved, especially lawsonite, offering a unique access to the understanding of deeply subducted terranes.Alpine Corsica consists of a complex stack of variably metamorphosed units of continental and Tethys-derived material. These units have been interpreted either as complex tectonic mixing formed during the Alpine subduction, or as more continuous portions of continental and/or oceanic lithosphere. The lack of detailed PT estimates over wide regions of the belt results in several uncertainties in identifying the boundaries separating units that experienced different tectono-metamorphic evolutions and, consequently, in the definition of an exhaustive architecture of the belt.Field, structural and metamorphic data collected in this study at different scales suggest that the Alpine Corsica belt is characterized by a high preservation of pre-Alpine sctructures, from the micro-scale up the scale of the belt, despite the intense deformation essociated with metamorphism, which locally reached lawsonite-eclogite metamorphism. In particular, only nine homogeneous tectono-metamorphic domains have been identified. These terranes can be referred to different paleogeographic domains that experienced different tectono-metamorphic evolutions.Despite that, geochronological data provided during this study indicate that Alpine Corsica results fro a complex polyphase evolution, being characterized by clear signature of both Alpine tectonics, at around 35 Ma, and Apennine tectonics, at around 25 Ma.Results provided in this paper contribute not only to the understanding of processes of subduction and mountain building, but also give important constraints for deciphering the Tethys-Alps and Alps-Apennine systems