Plagioclase Peridotites in Ocean-Continent Transitions: Refertilized Mantle Domains Generated by Melt Stagnation in the Shallow Mantle Lithosphere

The existence of different mantle domains exposed in ocean-continent transition zones provides a framework for understanding the generation of ultramafic seafloor along magma-poor rifted margins. In this study we present detailed petrological and geochemical data on peridotites from the Eastern Central Alps ophiolites in Switzerland and Italy to identify different mantle domains, to estimate the extent of refertilization, and to test whether refertilization is associated with a thermal signature that has important implications for geophysical interpretations of ocean-continent transitions. The compositions of clinopyroxene, orthopyroxene and spinel clearly reflect the different mantle domains. Relative to clinopyroxenes from spinel peridotites, clinopyroxenes from plagioclase peridotites have lower Na2O and Sr contents, but higher middle to heavy rare earth element ratios and Zr concentrations, and different Sc-V relationships. Spinels in plagioclase peridotites have higher TiO2 and lower Mg-numbers compared with those in spinel peridotites. Mineral-mineral trace element partitioning suggests that spinel peridotites equilibrated at substantially lower temperatures than plagioclase peridotites. The temperature difference between the spinel and plagioclase peridotites indicates an important thermal boundary between the two. The geochemical data show systematic spatial variations. A heterogeneous, ‘subcontinental domain' with no syn-rift melt imprint is separated from a ‘refertilized domain' that exhibits a complex history of regional-scale melt infiltration and melt-rock reaction, which has erased most of the ancient history. Simple calculations suggest that up to 12% of mid-ocean ridge basalt-type melt can be stored in plagioclase peridotite, relative to a depleted residue. Such a ‘lithospheric sponge' provides an explanation for the fertile compositions of the peridotites and the rare occurrence of volcanic rocks in magma-poor rifted margins. We suggest that magma-poor vs magma-rich margins are largely determined by the efficiency of melt extraction and not so much by melt generation processes, given a similar initial composition of the upwelling mantle. It is proposed that refertilization increases textural diversity and chemical heterogeneity related to shallow crystallization in the mantle lithospher

Gestion des émissions de poussières et de l'usage de l'eau lors de la circulation sur pistes non revêtues

Sur la plupart des chantiers de travaux publics, aussi bien dans le bâtiment ou sur les chantiers de construction et d'aménagement de voies de transport, la poussière est une source de nuisance majeure impactant aussi bien le chantier que son environnement. La poussière est une source de nuisance majeure impactant aussi bien le chantier que son environnement. Une meilleure gestion des émissions de poussière lors de travaux de terrassement peut permettre de réduire significativement les nuisances sur le site et ses alentours. Le guide « Recommandations pour la gestion des émissions de poussières et de l'usage de l'eau lors de la circulation sur pistes non revêtues » propose des méthodes de qualification des travaux et de l'environnement du site, de contrôle et de prévention des émissions de poussières, ainsi que de leur inhibition par arrosage : par l'évaluation des sols d'un site de travaux ; par l'évaluation du matériel d'arrosage ; par l'évaluation de l'environnement proche du site vis-à-vis de son exposition à la poussière

Refertilization of mantle peridotite in embryonic ocean basins: trace element and Nd isotopic evidence and implications for crust–mantle relationships

Many mantle peridotites exhumed along ancient and present-day magma-poor passive continental margins, along (ultra-) slow spreading ridges and fracture zones are plagioclase-bearing and generally too fertile to be the residue of partial melting processes alone. Likewise, the associated gabbroic and basaltic rocks are not a priori genetically linked to the underlying mantle rocks. Trace element and Nd isotopic studies in the eastern Central Alps peridotites in eastern Switzerland and northern Italy provide evidence for near-fractional melting and depletion at high pressure in Permian time followed by refertilization of subcontinental mantle by ascending melts at low pressure in Jurassic time. These results suggest regional-scale modification of ancient subcontinental mantle by melt infiltration and melt^rock reaction during incipient opening of oceanic basins. The similar Nd isotopic composition of plagioclase peridotite (ONd160 : 7.4^10.6) and associated mafic crust (ONd160 : 7.3^9.6) indicates that the liquids, which reacted with the peridotites derived from similar N-MORB type mantle sources. Plagioclase peridotites in magma-poor passive margins may predominantly form as a consequence of diffuse porous flow of melt in the thermal boundary layer above an upwelling asthenosphere and probably represent modified ancient subcontinental mantle. Thus, plagioclase peridotites exhumed in passive margins and possibly in (ultra-) slow spreading ridges may represent magma-poor periods where liquids stagnate in the thermal boundary layer and react with the surrounding peridotites. Once the effects of conductive heat loss dominate over advection of heat from below, diffuse porous flow of melt becomes less important and might be replaced by the formation of gabbro bodies

DAMPs and RAGE Pathophysiology at the Acute Phase of Brain Injury: An Overview

Early or primary injury due to brain aggression, such as mechanical trauma, hemorrhage or is-chemia, triggers the release of damage-associated molecular patterns (DAMPs) in the extracellular space. Some DAMPs, such as S100B, participate in the regulation of cell growth and survival but may also trigger cellular damage as their concentration increases in the extracellular space. When DAMPs bind to pattern-recognition receptors, such as the receptor of advanced glycation end-products (RAGE), they lead to non-infectious inflammation that will contribute to necrotic cell clearance but may also worsen brain injury. In this narrative review, we describe the role and ki-netics of DAMPs and RAGE at the acute phase of brain injury. We searched the MEDLINE database for “DAMPs” or “RAGE” or “S100B” and “traumatic brain injury” or “subarachnoid hemorrhage” or “stroke”. We selected original articles reporting data on acute brain injury pathophysiology, from which we describe DAMPs release and clearance upon acute brain injury, and the implication of RAGE in the development of brain injury. We will also discuss the clinical strategies that emerge from this overview in terms of biomarkers and therapeutic perspective

DAMPs and RAGE Pathophysiology at the Acute Phase of Brain Injury: An Overview

Early or primary injury due to brain aggression, such as mechanical trauma, hemorrhage or is-chemia, triggers the release of damage-associated molecular patterns (DAMPs) in the extracellular space. Some DAMPs, such as S100B, participate in the regulation of cell growth and survival but may also trigger cellular damage as their concentration increases in the extracellular space. When DAMPs bind to pattern-recognition receptors, such as the receptor of advanced glycation end-products (RAGE), they lead to non-infectious inflammation that will contribute to necrotic cell clearance but may also worsen brain injury. In this narrative review, we describe the role and ki-netics of DAMPs and RAGE at the acute phase of brain injury. We searched the MEDLINE database for “DAMPs” or “RAGE” or “S100B” and “traumatic brain injury” or “subarachnoid hemorrhage” or “stroke”. We selected original articles reporting data on acute brain injury pathophysiology, from which we describe DAMPs release and clearance upon acute brain injury, and the implication of RAGE in the development of brain injury. We will also discuss the clinical strategies that emerge from this overview in terms of biomarkers and therapeutic perspective

What is the tectono-metamorphic evolution of continental break-up: insights from the Tasna ocean-continent transition

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