Mechano-chemical feedbacks during deformation and hydration of peridotites

The hydration of the Earth’s mantle is a crucial process for many aspects of our planet, from the behaviour of the tectonic plates to the global water cycle and the origin of life. This process is called serpentinization and has a considerable impact on the rock’s behaviour when under stress. It makes rocks easier to break and is associated with a volume increase that can locally perturb tectonic stress and break surrounding rocks. The rock composing the mantle, peridotite, has however a very low permeability, and water has difficulties to circulate within it. Faulting is thus intimately linked to the water supply during serpentinization. Even though the link between faulting and serpentinization has been established, the way these two processes interact is not fully understood. Tectonically and seismically active zones in oceanic context are recognized to be preferred zones of serpentinization, but most common models for serpentinization do not reflect this major role of tectonics. This work highlights the role of tectonics in serpentinization initiation and maintenance through a combination of microstructural and seismic studies

Osmium isotope evidence for rapid melt migration towards the Moho in the Oman ophiolite

International audienc

Fracture network and serpentinization at oceanic spreading ridges: in-situ observations and comparison with a fossilized system

The efficiency of water transport to reactive peridotite is commonly the limiting factor for serpentinization of the lithospheric mantle to happen. This hydration process is typical of the oceanic lithosphere due to its thin crust and active fracturation, continuously creating new pathways for seawater, at ridge axis and subduction zones. Consequently, the extent of serpentinization is closely coupled with the intensity of the tectonic activity. Our study focuses on two sections of the South West Indian oceanic ridge, an ultra-slow spreading ridge. The very low melt production along this ridge type leads to extreme extensional regimes dominated by either magmatic or tectonic processes; this makes ultra-slow spreading ridges an ideal system to study the impact of magmatic vs tectonic extension on serpentinization along ridge axis. Three extensional regimes have been identified: volcanic, where the melt focuses leading to an up to 8 km thick basaltic crust, magmatic, characterized by a thin basaltic crust and deep seismic activity (down to 30 km depth), and amagmatic, characterized by peridotite covering the seafloor and even deeper seismic activity (down to 35 km depth). Aseismic zones are present at the surface of the magmatic and amagmatic regimes, likely associated with extensive serpentinization and efficient water supply. Based on seismic activity, we estimate that brittle damage can maintain high permeability in the case of the amagmatic and magmatic regimes while it is limited in the case of the volcanic regime. Our results indicate that oceanic ridges with spreading rates slower than 20 millimetres per year store at least 0.10 km3 of water per year in the oceanic mantle due to serpentinization. We compare these results with observations from serpentinized samples obtained during the 2018 Oman Drilling Project Phase 2. Samples have been drilled down to 400 m deep in the Oman Samail ophiolite and are composed of partially to completely serpentinized lithospheric dunite and harzburgite crosscut by multiple generations of magmatic dykes and serpentine veins. While the story of these rocks is complex, it is still possible to identify early features associated with on axis events. In agreement with our assumption that serpentinization is controlled by seismic damage, early fractures are commonly associated with enhanced serpentinization. We observe the dykes as being supplementary pathways for fluids

ESR and OSL variability in quartz extracted from magmatic, metamorphic or sedimentary rock

International audienceSediment routing systems in fluvial catchments are primarily governed by intertwined climatic, tectonic and man-induced drivers at the centennial/millennial timescales. Among the various geomor-phological and geochemical approaches developed to trace sediment dynamics, the scientific commu-nity has recently explored the potential of (palaeo-)dosimetric methods, which are extensively used to date e.g. Quaternary alluvial environments. Recently, Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) signals have been successfully transposed to decipher sediment prove-nance and transport in fluvial catchments. In this context, the French ANR QUARTZ research project aims at using quartz grains as an ubiquitous marker of sediment dynamics to understand (i) how each quartz grain holds a source-specific signature, and (ii) how this signature evolves along sediment routing systems. This contribu-tion specifically focuses on the first research topic.Quartz-bearing rocks located upstream in catchments deliver the material that is usually dated by OSL and/or ESR in fluvial sequences/deposits for geological or archaeological purposes. Here, we ana-lyzed with ESR and OSL methods quartz grains originating from different source rocks in the Streng-bach and Séveraisse catchments (France), draining a low mountain range (Vosges Mountains) and the Alps (Ecrins Massif), respectively. These rocks comprise magmatic, metamorphic and sedimentary lithologies of distinct age and composition, and provide quartz minerals present in the transposed and deposited sediments. The quartz grains were analyzed with ESR and OSL methods on the quartz min-erals from different quartz-bearing rock formations in both catchments, i.e. mostly granites, gneisses and sandstones of distinct ages and/or compositions. The source-specific signature of the different ESR signals (Ti/Al ratio, signal shape, non-optically bleachable intensity of the Al centre) was investigated. The bleaching kinetics of the different ESR centres used in dating and present in these quartz from different rock types were also investigated. Depending on the history of the quartz-bearing rock and therefore of the quartz nature (magmatic, metamorphic or sedimentary), we suggest that the ESR re-sponse varies in terms of signal shapes and intensity ratios of the different centres measured. Similar-ly, quartz OSL characteristics have been investigated (OSL signal intensities, contributions of fast/medium/slow OSL components, dose-response curves and saturation behavior) between rocks of different origins, as well as the bleaching potential (residual doses) between different quartz origins. These analyses are currently complemented in a near future by quantified trace element analyses on quartz samples from the same sources. This will allow us not only to provide encouraging results in terms of tracing quartz in fluvial deposits, but also a better understanding of the processes at the origin of ESR and OSL signals variability. This will constitute a first step towards understanding the dosi-metric behaviour of the sediments to be dated, and towards even more reliable dating techniques

ESR and OSL variability in quartz extracted from magmatic, metamorphic or sedimentary rock

International audienceSediment routing systems in fluvial catchments are primarily governed by intertwined climatic, tectonic and man-induced drivers at the centennial/millennial timescales. Among the various geomor-phological and geochemical approaches developed to trace sediment dynamics, the scientific commu-nity has recently explored the potential of (palaeo-)dosimetric methods, which are extensively used to date e.g. Quaternary alluvial environments. Recently, Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) signals have been successfully transposed to decipher sediment prove-nance and transport in fluvial catchments. In this context, the French ANR QUARTZ research project aims at using quartz grains as an ubiquitous marker of sediment dynamics to understand (i) how each quartz grain holds a source-specific signature, and (ii) how this signature evolves along sediment routing systems. This contribu-tion specifically focuses on the first research topic.Quartz-bearing rocks located upstream in catchments deliver the material that is usually dated by OSL and/or ESR in fluvial sequences/deposits for geological or archaeological purposes. Here, we ana-lyzed with ESR and OSL methods quartz grains originating from different source rocks in the Streng-bach and Séveraisse catchments (France), draining a low mountain range (Vosges Mountains) and the Alps (Ecrins Massif), respectively. These rocks comprise magmatic, metamorphic and sedimentary lithologies of distinct age and composition, and provide quartz minerals present in the transposed and deposited sediments. The quartz grains were analyzed with ESR and OSL methods on the quartz min-erals from different quartz-bearing rock formations in both catchments, i.e. mostly granites, gneisses and sandstones of distinct ages and/or compositions. The source-specific signature of the different ESR signals (Ti/Al ratio, signal shape, non-optically bleachable intensity of the Al centre) was investigated. The bleaching kinetics of the different ESR centres used in dating and present in these quartz from different rock types were also investigated. Depending on the history of the quartz-bearing rock and therefore of the quartz nature (magmatic, metamorphic or sedimentary), we suggest that the ESR re-sponse varies in terms of signal shapes and intensity ratios of the different centres measured. Similar-ly, quartz OSL characteristics have been investigated (OSL signal intensities, contributions of fast/medium/slow OSL components, dose-response curves and saturation behavior) between rocks of different origins, as well as the bleaching potential (residual doses) between different quartz origins. These analyses are currently complemented in a near future by quantified trace element analyses on quartz samples from the same sources. This will allow us not only to provide encouraging results in terms of tracing quartz in fluvial deposits, but also a better understanding of the processes at the origin of ESR and OSL signals variability. This will constitute a first step towards understanding the dosi-metric behaviour of the sediments to be dated, and towards even more reliable dating techniques

ESR and OSL variability in quartz extracted from magmatic, metamorphic or sedimentary rock

International audienceSediment routing systems in fluvial catchments are primarily governed by intertwined climatic, tectonic and man-induced drivers at the centennial/millennial timescales. Among the various geomor-phological and geochemical approaches developed to trace sediment dynamics, the scientific commu-nity has recently explored the potential of (palaeo-)dosimetric methods, which are extensively used to date e.g. Quaternary alluvial environments. Recently, Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) signals have been successfully transposed to decipher sediment prove-nance and transport in fluvial catchments. In this context, the French ANR QUARTZ research project aims at using quartz grains as an ubiquitous marker of sediment dynamics to understand (i) how each quartz grain holds a source-specific signature, and (ii) how this signature evolves along sediment routing systems. This contribu-tion specifically focuses on the first research topic.Quartz-bearing rocks located upstream in catchments deliver the material that is usually dated by OSL and/or ESR in fluvial sequences/deposits for geological or archaeological purposes. Here, we ana-lyzed with ESR and OSL methods quartz grains originating from different source rocks in the Streng-bach and Séveraisse catchments (France), draining a low mountain range (Vosges Mountains) and the Alps (Ecrins Massif), respectively. These rocks comprise magmatic, metamorphic and sedimentary lithologies of distinct age and composition, and provide quartz minerals present in the transposed and deposited sediments. The quartz grains were analyzed with ESR and OSL methods on the quartz min-erals from different quartz-bearing rock formations in both catchments, i.e. mostly granites, gneisses and sandstones of distinct ages and/or compositions. The source-specific signature of the different ESR signals (Ti/Al ratio, signal shape, non-optically bleachable intensity of the Al centre) was investigated. The bleaching kinetics of the different ESR centres used in dating and present in these quartz from different rock types were also investigated. Depending on the history of the quartz-bearing rock and therefore of the quartz nature (magmatic, metamorphic or sedimentary), we suggest that the ESR re-sponse varies in terms of signal shapes and intensity ratios of the different centres measured. Similar-ly, quartz OSL characteristics have been investigated (OSL signal intensities, contributions of fast/medium/slow OSL components, dose-response curves and saturation behavior) between rocks of different origins, as well as the bleaching potential (residual doses) between different quartz origins. These analyses are currently complemented in a near future by quantified trace element analyses on quartz samples from the same sources. This will allow us not only to provide encouraging results in terms of tracing quartz in fluvial deposits, but also a better understanding of the processes at the origin of ESR and OSL signals variability. This will constitute a first step towards understanding the dosi-metric behaviour of the sediments to be dated, and towards even more reliable dating techniques

ESR and OSL variability in quartz extracted from magmatic, metamorphic or sedimentary rock

International audienceSediment routing systems in fluvial catchments are primarily governed by intertwined climatic, tectonic and man-induced drivers at the centennial/millennial timescales. Among the various geomor-phological and geochemical approaches developed to trace sediment dynamics, the scientific commu-nity has recently explored the potential of (palaeo-)dosimetric methods, which are extensively used to date e.g. Quaternary alluvial environments. Recently, Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) signals have been successfully transposed to decipher sediment prove-nance and transport in fluvial catchments. In this context, the French ANR QUARTZ research project aims at using quartz grains as an ubiquitous marker of sediment dynamics to understand (i) how each quartz grain holds a source-specific signature, and (ii) how this signature evolves along sediment routing systems. This contribu-tion specifically focuses on the first research topic.Quartz-bearing rocks located upstream in catchments deliver the material that is usually dated by OSL and/or ESR in fluvial sequences/deposits for geological or archaeological purposes. Here, we ana-lyzed with ESR and OSL methods quartz grains originating from different source rocks in the Streng-bach and Séveraisse catchments (France), draining a low mountain range (Vosges Mountains) and the Alps (Ecrins Massif), respectively. These rocks comprise magmatic, metamorphic and sedimentary lithologies of distinct age and composition, and provide quartz minerals present in the transposed and deposited sediments. The quartz grains were analyzed with ESR and OSL methods on the quartz min-erals from different quartz-bearing rock formations in both catchments, i.e. mostly granites, gneisses and sandstones of distinct ages and/or compositions. The source-specific signature of the different ESR signals (Ti/Al ratio, signal shape, non-optically bleachable intensity of the Al centre) was investigated. The bleaching kinetics of the different ESR centres used in dating and present in these quartz from different rock types were also investigated. Depending on the history of the quartz-bearing rock and therefore of the quartz nature (magmatic, metamorphic or sedimentary), we suggest that the ESR re-sponse varies in terms of signal shapes and intensity ratios of the different centres measured. Similar-ly, quartz OSL characteristics have been investigated (OSL signal intensities, contributions of fast/medium/slow OSL components, dose-response curves and saturation behavior) between rocks of different origins, as well as the bleaching potential (residual doses) between different quartz origins. These analyses are currently complemented in a near future by quantified trace element analyses on quartz samples from the same sources. This will allow us not only to provide encouraging results in terms of tracing quartz in fluvial deposits, but also a better understanding of the processes at the origin of ESR and OSL signals variability. This will constitute a first step towards understanding the dosi-metric behaviour of the sediments to be dated, and towards even more reliable dating techniques

Seismic faults triggered early stage serpentinization of peridotites from the Samail Ophiolite, Oman

Serpentinization of mantle peridotites has first order effects on the rheology and tectonic behavior of the oceanic lithosphere, on the global water cycle, and on the biosphere at mid-oceanic ridges. Investigating serpentinization of abyssal peridotites is limited by the scarce occurrences of peridotites at or close to the ocean floor at slow and ultra-slow ridge environments where peridotite is exposed by long-lived detachments. The processes controlling hydration of the upper mantle below a thick magmatic crust at fast spreading ridges are poorly constrained. Here we present results based on samples from cores drilled in peridotites from the Samail ophiolite obtained during the Oman Drilling Project. We describe an early generation of highly localized brittle faults ubiquitous through all the peridotite cores and investigate their relation to the main serpentinization event represented by mesh-textured serpentinites. We combine microstructural observations with mineral and bulk chemical analyses as well as oxygen isotope microanalyses obtained by secondary ion mass spectrometry (SIMS). Asymmetric wall rock damage, weakening of crystal preferred orientation (CPO) in small fault clasts, and intense fragmentation within the fault zones even in association with very small displacements suggest that the early stage faults represent seismic events and predate mesh formation. Hydration and mesh texture formation follows in the wake of this faulting. Serpentinization is associated with moderate enrichment of fluid mobile elements including B, Li, Rb and U, indicative of fluid rock interaction characterized by relatively low fluid/rock ratios. This is consistent with a scenario where serpentinization took place below a thick magmatic crust following an earthquake-induced permeability increase. The oxygen isotope compositions of mesh serpentine are consistent with off-axis serpentinization at temperatures in the range 200-250 °CISSN:0012-821XISSN:1385-013

Creation of Quartz ID cards for source tracing using a multi-method approach as part of the ANR Quartz project: Lithium as a key element

International audienceQuartz is one of the most abundant minerals of the continental crust. Being highly resistant to weathering, it is ubiquitous in fluvial sediments and an ideal marker of their dynamics. The chemistry and physical properties of quartz are intricately linked and dependent on the mineral crystallization environment and subsequent history [1]. One of the main objectives of the French ANR Quartz project is to use this characteristic of quartz to trace its origin within fluvial sediments by combining conventional characterization methods with dosimetric methods such as Electronic Spin Resonance (ESR) and Optically Stimulated Luminescence (OSL) usually used for dating. The first step to this is the characterization of the quartz signature of each of the bedrocks of the watershed of interest. In this context, Li is a critical element to study. It is one of the main trace elements of quartz and has previously been reported as active in both paramagnetic and luminescent centers which are responsible for the signal measured by ESR and OSL techniques [2,3].In this study, we focus on the Strengbach watershed (French Vosges). Its relatively small size allowed for an exhaustive sampling of the various bedrocks, including granites, gneiss, Buntsandstein sandstones and hydrothermal fractures filled with quartz. Within these samples, quartz has been systematically analyzed using cathodoluminescence (CL), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and Laser Induced Breakdown Spectrometry (LIBS). Laser ablation of quartz is made difficult by its hardness and transparency which can lead to intensive tearing of the sample. To ensure usable data, analyses were made on thick (100 µm) rock sections and using a more energetic laser setup than usual. Bedrock samples have also been treated mechanically (grinding, sieving and magnetic separation) and chemically (HCl, H2SiF6 and heavy liquid separation) to extract quartz grains for Electronic Spin Resonance (ESR), Thermo-Luminescence (TL) and Optically Stimulated Luminescence (OSL) analyses.Results highlight the critical role of lithium in the definition of quartz origin signature. Concentration of Li and other main trace elements (such as Al, Ti) vary depending on quartz type and origin. However, the distinction is not complete between the different groups. CL, OSL and/or ESR signals are sensitive to chemistry but also to the position of foreign atoms within the quartz lattice, providing supplementary criteria for sample distinction. Interestingly, we report a discrepancy between the signal intensity of the ESR center associated with Li and the Li concentration likely indicating the occurrence of Li at several different sites within the mineral lattice. The combination of techniques is a valuable tool to better define the role(s) and positions of Li within the quartz lattice. This both helps better understand ESR and OSL signals, thus improving associated dating techniques, and sharpen differences between quartz signatures of the different Strengbach bedrocks.[1] J. Götze, Mineralogical magazine 73 (2009) 645-671[2] J. Götze, M. Plötze, D. Habermann, Mineralogy and Petrology 71 (2001) 225-250.[3] R.I. Mashkovtsev, Y. Pan, New Developments in Quartz Research: Varieties, Crystal Chemistry and Uses in Technology (2013)

Coupling dosimetric methods (luminescence and ESR) with hydrosedimentary connectivity to unravel source-to-sink dynamics in the Strengbach catchment (Eastern France)

International audienceSediment routing systems in fluvial catchments are primarily governed by intertwined climatic, tectonic and man-induced drivers at the centennial/millennial timescales. Among the various geomorphicical and geochemical approaches developed to trace sediment dynamics, the scientific community has recently explored the potential of (palaeo-)dosimetric methods, which are extensively used to date e.g. Quaternary alluvial environments. Recently, optically Stimulated luminescence (OSL) and Electron Spin Resonance (ESR) signals have been successfully transposed to decipher sediment provenance and transport in fluvial catchments. In parallel, the index of connectivity has been growingly used to quantitatively assess catchment-scale hydrosedimentary connectivity over the last decade. Against this framework, the French ANR QUARTZ research project aims at using quartz grains as an ubiquitous marker of sedimentary dynamics to understand (i) how each quartz grain holds a source-specific signature, and (ii) how this signature evolves along sediment routing systems. This study specifically focuses on the second aim. Longitudinal measurements of OSL and ESR signals from modern river borne sediments are performed together with the assessment of the catchment-scale index of connectivity. It is argued here that coupling both information can help to quantitatively unravel source-to-sink sedimentary dynamics. More precisely, the longitudinal evolution of ESR and OSL residual doses in quartz sediments is reconstructed. Whilst a downstream decrease of residual doses is expected owing to increasing duration to light exposure with increasing transport distance, sediment inputs from tributaries can blur this signal. Here, this relation between bleaching evolution of quartz and sediments inputs is investigated via the index of connectivity. A first campaign was performed in the Strengbach catchment in the Vosges Mountains (Eastern France) as it represents an ideal natural laboratory. Firstly, the geochemical composition of the source materials has been studied for more than thirty years. Secondly, it contains various quartz-bearing formations, i.e. plutonic, metamorphic and sedimentary. Finally, it displays a simple geomorphic configuration with (i) well-identified sources in the Vosges Mountains, (ii) a deeply-incised main valley with absence of significant intermediate storage (e.g. no terrace system) and (iii) a clear, single sink (Upper Rhine Graben). This allows representative computation of the index of connectivity (or dysconnectivity)