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Rosenberg C.L.,University Pierre and Marie Curie | Rosenberg C.L.,CNRS Paris Institute of Earth Sciences | Kissling E.,ETH Zurich
Geology | Year: 2013

Accommodation of collisional shortening in the Central Alps varies dramatically along strike, and this change is inferred to result from along-strike changes of rheology. In the western Central Alps, 90% of shortening is accommodated in the thickened lower plate. In the eastern Central Alps, 90% of shortening is accommodated in the upper plate. In the central Central Alps, shortening is almost equally partitioned between the two plates. The lower crust of the Adriatic plate forms a wedge that reaches a maximum north-south extension of almost 70 km in the Engadine section, progressively decreasing westward and disappearing along the Simplon section. This difference indicates an along-strike increase of intra-plate decoupling, limiting shortening of the Adriatic plate to the middle and upper parts of the crust. Whereas the upper plate indents into the thickened accreted lower plate in the Simplon section, it is the lower plate that indents an intensely deforming upper plate in the Engadine section. In the west, the Ivrea mantle body increases the strength of the Adriatic upper plate, and Barrovian metamorphism weakens the lower plate. Therefore, along-strike transfer of shortening from one plate to the other appears to be a manifestation of along-strike changes in rheology deep in the crust. © 2013 Geological Society of America. Source

Chorowicz J.,CNRS Paris Institute of Earth Sciences
Comptes Rendus - Geoscience | Year: 2016

The Pieniny Klippen Belt (PKB) is a narrow, discontinuous zone rich in olistostromes and olistoliths (Klippen) in the western Carpathians. This paper, based on prior works including tectonic and stratigraphic evidences, suggests that the PKB rocks were deposited from the Triassic to the Early Paleogene along the eastern footwall of a major Split-Karlovac-Initial PKB-Crustal-Zone (SKICZ) paleotransform fault zone. This transform fault was then separating the continental crust of the Austro-Alpine zone in the west and a Carpathian Embayment Ocean in the east. It was only during the Late Paleogene-Early Miocene that the PKB rocks were integrated into the accretionary prism that formed at the front of the eastward-extruded ALCAPA units. This interpretation therefore supports the existence of a major paleotransform fault zone in the Neo-Tethys during the Triassic-Early Paleogene. This paleotransform had been previously suggested to explain the observed reversal in obduction and subduction at the junction between the eastern-southern Alps and the Carpathians-Dinarides. © 2015 Académie des sciences. Source

Le Pourhie L.,CNRS Paris Institute of Earth Sciences | Le Pourhie L.,French National Center for Scientific Research | Saleeby J.,California Institute of Technology
Geology | Year: 2013

Along the western border of the Sierra Nevada microplate, the San Andreas fault (California, United States) is comprised of three segments. Two (north and south segments) are locked and support large earthquakes (e.g., the M 7.7 1906 San Francisco and the M 7.8 1857 Fort Tejon earthquakes), while the central segment, from Parkfield to San Juan Bautista, is creeping. Based on mechanical models, we show that the late Pliocene-Quaternary convective removal (delamination) of the southern Sierra Nevada mantle lithosphere and associated uplift of the Sierra Nevada Mountains causes the Great Valley upper crust to deform by flexure and buckling. Additional three-dimensional flexural models imply that the local flexural bulge overlaps with the creeping segment of the fault system, while geological observations indicate that the local weakening of the San Andreas fault started at the same time that the Sierra Nevada started its recent phase of uplift. We argue that bending stresses promote lithostatic pore pressure to occur in the depth range of 7-15 km, causing the effective strength of the fault to vanish, and locally favoring creep. Our results suggest for the first time that earthquake cycles along a major plate boundary may be influenced by convective instabilities in the adjacent upper mantle. © 2013 Geological Society of America. Source

Tribovillard N.,Lille University of Science and Technology | Algeo T.J.,University of Cincinnati | Baudin F.,CNRS Paris Institute of Earth Sciences | Riboulleau A.,Lille University of Science and Technology
Chemical Geology | Year: 2012

Patterns of uranium-molybdenum covariation in marine sediments have the potential to provide insights regarding depositional conditions and processes in paleoceanographic systems. Specifically, such patterns can be used to assess bottom water redox conditions, the operation of metal-oxyhydroxide particulate shuttles in the water column, and the degree of water mass restriction. The utility of this paleoenvironmental proxy is due to the differential geochemical behavior of U and Mo: (1) uptake of authigenic U by marine sediments begins at the Fe(II)-Fe(III) redox boundary (i.e., suboxic conditions), whereas authigenic Mo enrichment requires the presence of H 2S (i.e., euxinic conditions), and (2) transfer of aqueous Mo to the sediment may be enhanced through particulate shuttles, whereas aqueous U is unaffected by this process. In the present study, we examine U-Mo covariation in organic-rich sediments deposited mostly in the western Tethyan region during oceanic anoxic events (OAEs) of Early Jurassic to Late Cretaceous age. Our analysis generally confirms existing interpretations of redox conditions in these formations but provides significant new insights regarding water mass restriction and the operation of particulate shuttles in depositional systems. These insights will help to address contentious issues pertaining to the character and origin of Mesozoic OAEs, such as the degree to which regional paleoceanographic factors controlled the development of the OAEs. © 2011 Elsevier B.V. Source

Sanloup C.,CNRS Paris Institute of Earth Sciences
Chemical Geology | Year: 2016

Knowing the density of silicate liquids at high pressure is essential to answer questions relevant to the presence of magmas at depth, whether that be in the present Earth or in its earliest times, during differentiation of the planet. Melts have unique physical and chemical properties, which vary as a function pressure, and chemical composition. The focus here will be on in situ measurements of the density of magmas, with a presentation of the available methods and of the main results obtained so far, including why some magmas may be trapped at depth. Understanding the macroscopical physical properties of magmas requires an accurate microscopic structural description. Structural descriptions of compressed magmas are becoming more widely available, from experiments and from theoretical calculations. These structural inputs are used to understand the compression mechanisms at stake in the densification of magmas, e.g. the collapse of voids, coordination increase for the major cations, and bond compressibility. These densification processes profoundly affect not only the physical properties of the melt, but also its chemical properties, i.e. the way element partition between the magma and a metallic melt or between the magma and crystals. © 2016 Elsevier B.V. Source

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