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Contractional relay zones between pairs of normal faults are sometimes associated with multiple antithetic faults in a geometry similar to that found in Riedel shear zones. Detailed fault displacement profiles of outcrop examples of this geometry demonstrate that the antithetic faults accommodate the transfer of displacement between the synthetic faults that bound the relay zones. The throw on individual antithetic faults, or R′ shears, is typically constant across relay zones while the throw profile on the synthetic faults, or R shears, is stepped; the steps occurring across branchpoints with abutting R’ shears. Transfer of fault displacement occurs by a combination of block rotation and irrotational block translation within the relay zone. As fault throw increases, contractional relay zones are by-passed by the linkage of the synthetic faults, in a manner analogous to the formation of P-shears by the linkage of R shears in classic Riedel shear experiments, but with the original relay zone structure still preserved within the fault zone. With yet further strain bedding may rotate into near-parallelism with the fault surface, with the original geometrical configuration of the relay zone difficult to unravel.

International audience

National audience; The continental rifted margins of Mozambique provide an excellent example ofcontinental passive margins with a significant structural variability associated tomagmatism and inheritance. Despite accumulated knowledge in this area, the tectonicstructure and nature of the crust from Mozambique margins, especially the Limpopotransform margin are still poorly known. Here, we use high-resolution seismicreflection dataset and wells from industry to propose a structural interpretation of thisarea.Our results indicate that the Limpopo transform fault zone limits a continental crustwestward, with deep Karoo grabens, from an oceanic crust domain eastward. TheLimpopo transform margin also shows a widespread magmatism, attested by thepresence of lava flows and highly magmatic oceanic crust, implying different thermalperturbations through time and space.We suggest that the expression of thermal perturbations started with the Karoo LargeIgneous province emplacement at about 180 Ma. This intense magmatism event isfavored by pre-existing and neo-formed faults, which may contribute significantly to thedistribution of magma generated. We propose an evolution model from the onset of therifted margin to the seafloor spreading along the Limpopo magma-rich transformmargin with (i) an E-W extension trend responsible for the formation of a large faultcontrolledbasin during the Permo-Trias (T1); (ii) the extension becoming NNW-SSE,oblique to the margin direction as attested by the presence of flower structures, allowsfor reactivation of previous structures inducing the deposition of a volcanosedimentarywedge, and the formation of several magmatic infilling during the Jurassic(T2); (iii) the onset of oceanic spreading after ca. M25 (i.e. 156 Ma) in the Limpopo areawhich triggered the uplift and erosion of the proximal parts of the margin as well as theformation of several other magmatic infilling (T3).

International audience; A new geophysical and geological dataset, acquired during the SISMAORE oceanographic campaign (2020-2021), reveals a recent tectonic and volcanic deformation distributed over 130km in the abyssal plain that permit to unravel the unconstrained lithospheric plate boundaries between Lwandle and Somalia blocks and the controversial origin of the Comoros Archipelago.Two recent submarine volcanic and tectonic provinces of 5000km2 , with a large number of varied volcanic structures and faults, are unveiled: the N160° N'Droundé (north of GrandeComore) and the N130° Mwezi provinces (north of Anjouan/Mayotte). Dredged Mwezi rocks suggest a recent gas-rich volcanic activity. It is also identified a recent N130° trending volcanic structures (cones, lava flows, eruptive fissures) between Anjouan and Mayotte in agreement with the presence of shallow earthquakes, and also recent lava flows on the southern flanks of the Grande Comore and Moheli. Southwards, recent sedimentation is important with no volcanism and deformation. A consistent sedimentary thickness covers the flanks of Mayotte and Anjouan and the presence of large areas of submarine instability at the foot and on the slope of the islands is confirmed.These first observations suggest a transtensional deformation, accommodated by dextral strike-slip motion, strongly influenced by pre-existing structuration of the Mesozoic oceanic crust and by the East Africa Rift system. The 130km wide zone of intraplate deformationcharacterizes an immature lithospheric plate boundary of the north Lwandle block.

International audience; Slab tearing induces localized deformations in the overriding plates of subduction zones and transfer zones accommodating differential retreat in back-arc regions. Because the space available for retreating slabs is limited in the Mediterranean realm, slab tearing during retreat has been a major ingredient of the evolution of this region since the end of the Eocene. The association of detailed seismic tomographic models and extensive field observations makes the Mediterranean an ideal natural laboratory to study these transfer zones. We review in this paper the various structures in back-arc regions differential retreat from the Alboran Sea to the Aegean-Anatolian region and discuss them with the help of 3D numerical models to better understand the partitioning of deformation between high-angle and low-angle faults, as well as the 3-D kinematics of deformation in the middle and lower crusts. Simple, archetypal, crustal-scale strike-slip faults are in fact rare in these contexts above slab tears. Transfer zones are in general instead wide deformation zones, from several tens to several hundred kilometers. A partitioning of deformation is observed between the upper and the lower crust with low-angle extensional shear zones at depth and complex association of transtensional basins at the surface. In the Western Mediterranean, between the Gulf of Lion and the Valencia basin, transtensional strike-slip faults are associated with syn-rift basins and lower crustal domes elongated in the direction of retreat (a-type domes), associated with massive magmatic intrusions in the lower crust and volcanism at the surface. On the northern side of the Alboran Sea, wide E-W trending strike-slip zones in the brittle field show partitioned thrusting and strike-slip faulting in the external zones of the Betics, and E-W trending metamorphic core complexes in the internal zones, parallel to the main retreat direction with a transition in time from ductile to brittle deformation. On the opposite, the southern margin of the Alboran Sea shows short en-échelon strike-slip faults. Deep structures are not known there. In the Aegean-Anatolian region, two main tear faults with different degrees of maturity are observed. Western Anatolia (Menderes Massif) and the Eastern Aegean Sea evolved above a major left-lateral tear in the Hellenic slab. In the crust, the differential retreat was accommodated mostly by low-angle shear zones with a constant direction of stretching and the formation of a-type high-temperature domes exhumed from the middle and lower crust. These low-angle shear zones evolve through time from ductile to brittle. On the opposite side of the Aegean region, the Corinth and Volos Rift as well as the Kephalonia fault offshore, accommodate the formation of a dextral tear fault. Here, only the brittle crust can be observed, but seismological data suggest low-angle shear zones at depth below the rifts. We discuss the rare occurrence of pure strike-slip faults in these contexts and propose that the high heat flow above the retreating slabs and more especially above slab tears favors a ductile behavior with distributed deformation of the crust and the formation of low-angle shear zones and high-temperature domes. While retreat proceeds, aided by tears, true strike-slip fault system may localize and propagate toward the retreating trench, ultimately leading to the formation of new plate boundary, as shown by the example of the North Anatolian Fault.; Les déchirures des panneaux plongeants dans les zones de subduction induisent des déformations localisées dans les domaines arrière-arcs des plaques chevauchantes sous la forme de zones de transfert qui accommodent les différences latérales de vitesse de retrait des fosses. Parce que l’espace disponible pour ce retrait est limité dans le domaine méditerranéen, les déchirures ont joué un rôle majeur dans l’évolution de cette région depuis la fin de l’Eocène. L’association de modèles tomographiques détaillés et de nombreuses observations de terrain font de la Méditerranée un laboratoire naturel idéal pour étudier ces zones de transfert. Nous proposons ici une revue des diverses structures des domaines arrière-arc accommodant le retrait différentiel depuis la Mer d’Alboran jusqu’à la région égéenne et nous les discutons grâce à des modèles numériques 3-D pour mieux comprendre le partitionnement de la déformation entre les failles à fort et faible pendage et la cinématique 3-D dans la croûte moyenne et la croûte inférieure. Nous montrons que les failles localisées purement décrochantes d’échelle crustale sont rares au-dessus de ces zones de déchirure. Les zones de transfert sont au contraire plutôt des zones de déformation larges de quelques dizaines à quelques centaines de kilomètres. On y observe un partitionnement de la déformation entre la croûte supérieure et la croûte inférieure avec des zones de cisaillement extensives à faible pendage en profondeur et une association complexe de bassins en transtension et de détachements dans la croûte supérieure. En Méditerranée occidentale, entre Golfe du Lion et bassin de Valence, des failles décrochantes transtensives sont associées à des bassins syn-rift et des dômes de croûte inférieure allongés dans la direction du retrait (dômes de type « a »), associés à des intrusions magmatiques massives dans la croûte inférieure et du volcanisme en surface. Sur la marge septentrionale de la Mer d’Alboran, des zones décrochantes E-O larges dans le domaine cassant montrent un partitionnement entre des chevauchements et des décrochements dans les zones externes et des dômes métamorphiques allongés E-O dans les zones internes, parallèlement à la direction principale de retrait, avec une évolution du ductile vers le cassant au cours du temps. La rive sud de la Mer d’Alboran montre à l’opposé des failles décrochantes en échelon courtes et les structures profondes sont mal connues. Dans la région Egée-Anatolie, deux zones larges de degré de maturité différents sont observées. L’ouest de l’Anatolie (massif du Menderes) et l’est de la Mer Egée ont évolué au-dessus d’une déchirure majeure du panneau plongeant hellénique. Dans la croûte, le retrait différentiel est principalement accommodé par des zones de cisaillement extensives à faible pendage avec des directions d’étirement cohérentes régionalement et des dômes métamorphiques de type « a » et de haute température exhumés depuis la croûte moyenne et la croûte inférieure. Ces zones de cisaillement à faible pendage évoluent du ductile au cassant au cours du temps. Du côté opposé du domaine égéen, le rift de Corinthe, le rift de Volos, ainsi que la faille de transfert de Céphalonie accommodent la formation d’une large zone de transfert dextre. Dans cette région, seule la croute supérieure peut être observée, mais les données sismologiques suggèrent l’existence de zones de cisaillement à faible pendage sous les rifts actifs. Nous discutons la rareté des grandes failles de transfert purement décrochantes dans ces contextes et proposons que le flux de chaleur élevé au-dessus des panneaux plongeants en recul et plus encore au-dessus des zones de déchirures favorise un comportement ductile avec déformation distribuée de la croûte et la formation de zones de cisaillement à faible pendage et de dômes de haute température. Pendant le retrait, favorisé par ces déchirures, de véritables failles décrochantes lithosphériques peuvent ensuite se localiser et évoluer en limites de plaques, comme le montre l’exemple de la Faille Nord Anatolienne.

International audience; Abstract. Back-arc extension superimposed on mountain belts leads to distributed normal faults and shear zones interacting with magma emplacement within the crust. The composition of granitic magmas emplaced at this stage often involves a large component of crustal melting. The Miocene Aegean granitoids were emplaced in metamorphic core complexes (MCCs) below crustal-scale low-angle normal faults and ductile shear zones. Intrusion processes interact with extension and shear along detachments, from the hot magmatic flow within the pluton root zone to the colder ductile and brittle deformation below and along the detachment. A comparison of the Aegean plutons with the island of Elba MCC in the back-arc region of the Apennine subduction shows that these processes are characteristic of pluton–detachment interactions in general. We discuss a conceptual emplacement model, tested by numerical models. Mafic injections within the partially molten lower crust above the hot asthenosphere trigger the ascent within the core of the MCC of felsic magmas, controlled by the strain localization on persistent crustal-scale shear zones at the top that guide the ascent until the brittle ductile transition. Once the system definitely enters the brittle regime, the detachment and the upper crust are intruded, while new detachments migrate upward and in the direction of shearing.

Most of the previous works on data flow optimizations for Machine Learning hardware accelerators try to find algorithmic re-factorization such as loop-reordering and loop-tiling. However, the analysis and information they provide are still at very high level and one must further map them onto instructions that hardware can understand. This paper presents "Dijkstra-Through-Time" (DTT), an ahead of time compute and memory scheduling-mapping algorithm for deterministic workloads. It provides a simple implementation and supports accelerators with complex NoC configurations, at the expense of a long compilation process. This initial paper illustrates a proof of concept implementation to merge scheduling and data cache coherence mechanisms to get more optimized data flows., Comment: The paper contains 7 pages and 10 figures. It is the result of the work performed during an internship at Nokia Bell Labs (Antwerp) in 2020

International audience; Slab tearing induces localized deformations in the overriding plates of subduction zones and transfer zones accommodating differential retreat in back-arc regions. Because the space available for retreating slabs is limited in the Mediterranean realm, slab tearing during retreat has been a major ingredient of the evolution of this region since the end of the Eocene. The association of detailed seismic tomographic models and extensive field observations makes the Mediterranean an ideal natural laboratory to study these transfer zones. We review in this paper the various structures in back-arc regions differential retreat from the Alboran Sea to the Aegean-Anatolian region and discuss them with the help of 3D numerical models to better understand the partitioning of deformation between high-angle and low-angle faults, as well as the 3-D kinematics of deformation in the middle and lower crusts. Simple, archetypal, crustal-scale strike-slip faults are in fact rare in these contexts above slab tears. Transfer zones are in general instead wide deformation zones, from several tens to several hundred kilometers. A partitioning of deformation is observed between the upper and the lower crust with low-angle extensional shear zones at depth and complex association of transtensional basins at the surface. In the Western Mediterranean, between the Gulf of Lion and the Valencia basin, transtensional strike-slip faults are associated with syn-rift basins and lower crustal domes elongated in the direction of retreat (a-type domes), associated with massive magmatic intrusions in the lower crust and volcanism at the surface. On the northern side of the Alboran Sea, wide E-W trending strike-slip zones in the brittle field show partitioned thrusting and strike-slip faulting in the external zones of the Betics, and E-W trending metamorphic core complexes in the internal zones, parallel to the main retreat direction with a transition in time from ductile to brittle deformation. On the opposite, the southern margin of the Alboran Sea shows short en-échelon strike-slip faults. Deep structures are not known there. In the Aegean-Anatolian region, two main tear faults with different degrees of maturity are observed. Western Anatolia (Menderes Massif) and the Eastern Aegean Sea evolved above a major left-lateral tear in the Hellenic slab. In the crust, the differential retreat was accommodated mostly by low-angle shear zones with a constant direction of stretching and the formation of a-type high-temperature domes exhumed from the middle and lower crust. These low-angle shear zones evolve through time from ductile to brittle. On the opposite side of the Aegean region, the Corinth and Volos Rift as well as the Kephalonia fault offshore, accommodate the formation of a dextral tear fault. Here, only the brittle crust can be observed, but seismological data suggest low-angle shear zones at depth below the rifts. We discuss the rare occurrence of pure strike-slip faults in these contexts and propose that the high heat flow above the retreating slabs and more especially above slab tears favors a ductile behavior with distributed deformation of the crust and the formation of low-angle shear zones and high-temperature domes. While retreat proceeds, aided by tears, true strike-slip fault system may localize and propagate toward the retreating trench, ultimately leading to the formation of new plate boundary, as shown by the example of the North Anatolian Fault.; Les déchirures des panneaux plongeants dans les zones de subduction induisent des déformations localisées dans les domaines arrière-arcs des plaques chevauchantes sous la forme de zones de transfert qui accommodent les différences latérales de vitesse de retrait des fosses. Parce que l’espace disponible pour ce retrait est limité dans le domaine méditerranéen, les déchirures ont joué un rôle majeur dans l’évolution de cette région depuis la fin de l’Eocène. L’association de modèles tomographiques détaillés et de nombreuses observations de terrain font de la Méditerranée un laboratoire naturel idéal pour étudier ces zones de transfert. Nous proposons ici une revue des diverses structures des domaines arrière-arc accommodant le retrait différentiel depuis la Mer d’Alboran jusqu’à la région égéenne et nous les discutons grâce à des modèles numériques 3-D pour mieux comprendre le partitionnement de la déformation entre les failles à fort et faible pendage et la cinématique 3-D dans la croûte moyenne et la croûte inférieure. Nous montrons que les failles localisées purement décrochantes d’échelle crustale sont rares au-dessus de ces zones de déchirure. Les zones de transfert sont au contraire plutôt des zones de déformation larges de quelques dizaines à quelques centaines de kilomètres. On y observe un partitionnement de la déformation entre la croûte supérieure et la croûte inférieure avec des zones de cisaillement extensives à faible pendage en profondeur et une association complexe de bassins en transtension et de détachements dans la croûte supérieure. En Méditerranée occidentale, entre Golfe du Lion et bassin de Valence, des failles décrochantes transtensives sont associées à des bassins syn-rift et des dômes de croûte inférieure allongés dans la direction du retrait (dômes de type « a »), associés à des intrusions magmatiques massives dans la croûte inférieure et du volcanisme en surface. Sur la marge septentrionale de la Mer d’Alboran, des zones décrochantes E-O larges dans le domaine cassant montrent un partitionnement entre des chevauchements et des décrochements dans les zones externes et des dômes métamorphiques allongés E-O dans les zones internes, parallèlement à la direction principale de retrait, avec une évolution du ductile vers le cassant au cours du temps. La rive sud de la Mer d’Alboran montre à l’opposé des failles décrochantes en échelon courtes et les structures profondes sont mal connues. Dans la région Egée-Anatolie, deux zones larges de degré de maturité différents sont observées. L’ouest de l’Anatolie (massif du Menderes) et l’est de la Mer Egée ont évolué au-dessus d’une déchirure majeure du panneau plongeant hellénique. Dans la croûte, le retrait différentiel est principalement accommodé par des zones de cisaillement extensives à faible pendage avec des directions d’étirement cohérentes régionalement et des dômes métamorphiques de type « a » et de haute température exhumés depuis la croûte moyenne et la croûte inférieure. Ces zones de cisaillement à faible pendage évoluent du ductile au cassant au cours du temps. Du côté opposé du domaine égéen, le rift de Corinthe, le rift de Volos, ainsi que la faille de transfert de Céphalonie accommodent la formation d’une large zone de transfert dextre. Dans cette région, seule la croute supérieure peut être observée, mais les données sismologiques suggèrent l’existence de zones de cisaillement à faible pendage sous les rifts actifs. Nous discutons la rareté des grandes failles de transfert purement décrochantes dans ces contextes et proposons que le flux de chaleur élevé au-dessus des panneaux plongeants en recul et plus encore au-dessus des zones de déchirures favorise un comportement ductile avec déformation distribuée de la croûte et la formation de zones de cisaillement à faible pendage et de dômes de haute température. Pendant le retrait, favorisé par ces déchirures, de véritables failles décrochantes lithosphériques peuvent ensuite se localiser et évoluer en limites de plaques, comme le montre l’exemple de la Faille Nord Anatolienne.

International audience; The break-up of the Gondwana supercontinent started during the Early Jurassic and lead to the formation of the Mozambique passive margins, as Africa and Antarctica separated during the mid-Jurassic period. Albeit plate kinematics during the oceanic spreading stage are relatively well constrained, the initial fit of Africa and Antarctica, their earliest relative movements and the architecture of distinct margin segments from Mozambique to South Africa in relation to those from Antarctica remain sparsely known. While margins architecture has been recently evidenced along the central Mozambique, the spatial extent of rifting further south remains poorly documented.Based on detailed observations related to seismic reflection profiles and oil company wells, findings show the existence of a magma-rich segment with large volume of seaward dipping reflectors in the South Mozambique (i.e. the Natal segment). Such segment is defined by a rapid transition from continental to oceanic domains that differs from classical divergent margins. Such particular architecture may be related to a difference in lithosphere rheology (i.e. Archean vs. Neoproterozoic) that favored extension and upwelling from a deep thermomechanical anomaly, called Karoo superplume. In parallel, the birth of the Natal ocean occurred at ca. 165 - 160 Ma and bring new constrains on Gondwana breakup. Here, we inferred a simplified conceptual geodynamic model for the whole area, from the initiation of extension to the seafloor spreading. We summarize this evolution in three main steps. Stage T1 represents the first extensional event inducing crustal thinning during the Permo-Trias before the breakup of the Gondwana. It is characterized by an E-W extension trend responsible for the formation of large N-S fault-controlled basins. Stage T2 is marked by the onset of a plume activity at about 180 Ma. Characterized by large N-S trending basins and by seawards dipping reflectors infilling, deformation related to T2 is consistent with a NW-SE trending extension. Finally, Stage T3 corresponds to the continuation of the rift with a stress field rotation ranging from NW-SE to N-S, suggesting that Antarctica moving in a SSE direction with respect to Africa after 156 Ma. The entire region is then going through an episode of uplift related to mantle dynamics.

International audience; The Karoo Large Igneous Province is one of the most extensively studied continental trapp [1, 2 and reference therein]. Nonetheless the nature, composition and origin of some parts of this province, and principally its youngest portions outcropping within the Lebombo province remain unclear [3]. Moreover the relationships between this province, the volcanic Mozambique oblique margin formation and the Gondwana break up are still highly debated. To better understand the composition of the mantle source(s) from which the melts originated and their geodynamic implication from Jurassic times to oceanisation within the Mozambique Channel we studied volcanic and plutonic samples from several drill holes within the South MozambicanCoastal Plain (SMCP) as well as samples from the Movene and the Bumbeni complex areas. Weconducted major, trace elements and radiogenic isotopes (Sr, Nd, Pb) analyses as well as 40Ar/39Ar dating. Our results clearly demonstrate that the SMCP basement is composed of continental lithosphere more or less modified by mantle magmatism as expected in a continental flood basalt setting. Conversely to some previous interpretations no oceanic crust is present within the SMCP which has important implications for the initial Gondwana fit[4].Our results indicate that a plume-type mantle source, more or less influenced by Sub-Continental Lithospheric Mantle and Upper Depleted ambient Mantle, is involved in the formation of all Karoo-related magmatism episodes in the area. The isotope composition of the African mantle plume is highly comparable to the one of the Afar plume suggesting that the thermal anomaly may have been active for about 200 Ma. [1] Cox, (1988) InContinental Flood Basalts, Spinger; [2] Jourdan et al.,(2007), J. Petrol.,48:1043-1077; [3] Melluso et al., (2008), J. South Af. Earth Sci.52:139-151; [4] Thompson et al., (2019) Earth Science Reviews191:26-56

Virtual Conference; International audience

High temperature geothermal resources are mainly located along subduction zones. The Menderes geothermal Province (Turkey) offers the opportunity to study amagmatic geothermal systems, without necessarily invoking a magmatic heat source in the upper crust. This study shows that high temperatures in the back-arc domain are primarily related to subduction dynamics (i.e. rollback and tearing). Numerical models suggest that shear heating and mantle flows increase temporarily the amount of heat flow at the base of the crust. Furthermore, field studies on the entire Aegean region (Cyclades, Dodecanese and Western Anatolia) show a similar tectonic and thermal evolution since the Cretaceous, characterized by a succession of episodes of HP-LT and HT-LP metamorphism. Moreover, the contribution of TRSCM and radiochronometric data (⁴⁰Ar-³⁹Ar, U-Pb) reveals the formation of a largethermal pulse contemporaneous with the exhumation of the Menderes MCC. This event occurs in the Miocene and may be explained by a drastic change in subduction dynamics (i.e. slab tearing under the Menderes Massif).Crustal-scale structures (i.e. detachments) induce the emplacement of the Menderes MCC, and also control deep fluids circulation in the crust from brittle-ductile transition zone to the surface without magmatic contribution inthe upper crust. As a consequence, the Menderes geothermal Province is recognized as a most important active geothermal province in the world because it results from subduction dynamics. This dynamics thus controls thespatial and temporal distribution of thermal anomaly and extension, inducing crustal-scale permeable structures(detachments) that enhance fluids circulation.; Les ressources géothermales de haute température se localisent principalement le long des zones de subduction. Considérée comme amagmatique, la Province géothermale du Menderes (Turquie) offre l’opportunité d’étudier des systèmes géothermaux sans nécessairement invoquer une source de chaleur magmatique dans les premiers kilomètres de la croûte. Cette étude montre que les températures anormalement élevées dans la zone d’arrière-arcs sont principalement liées à la dynamique particulière de la subduction est-méditerranéenne (i.e. retrait et déchirure). Les résultats de modèles numériques suggèrent que le shear heating et les flux mantelliques modifient temporairement la quantité du flux de chaleur à la base de croûte. Par ailleurs, des études de terrain sur l’ensemble de la région (Cyclades, Dodécanèse et Anatolie occidentale) montrent une évolution tectonique et thermique similaire depuis le Crétacé, marquée minéralogiquement par une succession d’épisodes de HP-BT puis de HT-BP. Toutefois, l’apport des données TRSCM et radiochronométriques (⁴⁰Ar-³⁹Ar, U-Pb) souligne un évènement thermique majeur contemporain à la mise en place du dôme métamorphique du Menderes. Cet événement que l’on explique par un changement drastique de la dynamique de subduction (i.e. déchirure du panneau plongeant sous le Massif du Menderes), se développe au Miocène. Des structures d’échelle crustale (i.e. détachements)accommodent la mise en place du Massif du Menderes et contrôlent la circulation des fluides dans la croûte, depuis la zone de transition fragile-ductile jusqu’à la surface, sans nécessairement impliquer la contribution de systèmes magmatiques dans la croûte supérieure. La Province géothermale du Menderes est considérée comme une province de haute température de taille mondiale car elle résulte de la dynamique de subduction qui contrôle spatialement et temporellement l’intensité de l’anomalie thermique mais également la mise en place de structures perméables(détachements) d’échelle crustale favorisant la circulation des fluides.

High temperature geothermal resources are mainly located along subduction zones. The Menderes geothermal Province (Turkey) offers the opportunity to study amagmatic geothermal systems, without necessarily invoking a magmatic heat source in the upper crust. This study shows that high temperatures in the back-arc domain are primarily related to subduction dynamics (i.e. rollback and tearing). Numerical models suggest that shear heating and mantle flows increase temporarily the amount of heat flow at the base of the crust. Furthermore, field studies on the entire Aegean region (Cyclades, Dodecanese and Western Anatolia) show a similar tectonic and thermal evolution since the Cretaceous, characterized by a succession of episodes of HP-LT and HT-LP metamorphism. Moreover, the contribution of TRSCM and radiochronometric data (⁴⁰Ar-³⁹Ar, U-Pb) reveals the formation of a largethermal pulse contemporaneous with the exhumation of the Menderes MCC. This event occurs in the Miocene and may be explained by a drastic change in subduction dynamics (i.e. slab tearing under the Menderes Massif).Crustal-scale structures (i.e. detachments) induce the emplacement of the Menderes MCC, and also control deep fluids circulation in the crust from brittle-ductile transition zone to the surface without magmatic contribution inthe upper crust. As a consequence, the Menderes geothermal Province is recognized as a most important active geothermal province in the world because it results from subduction dynamics. This dynamics thus controls thespatial and temporal distribution of thermal anomaly and extension, inducing crustal-scale permeable structures(detachments) that enhance fluids circulation.; Les ressources géothermales de haute température se localisent principalement le long des zones de subduction. Considérée comme amagmatique, la Province géothermale du Menderes (Turquie) offre l’opportunité d’étudier des systèmes géothermaux sans nécessairement invoquer une source de chaleur magmatique dans les premiers kilomètres de la croûte. Cette étude montre que les températures anormalement élevées dans la zone d’arrière-arcs sont principalement liées à la dynamique particulière de la subduction est-méditerranéenne (i.e. retrait et déchirure). Les résultats de modèles numériques suggèrent que le shear heating et les flux mantelliques modifient temporairement la quantité du flux de chaleur à la base de croûte. Par ailleurs, des études de terrain sur l’ensemble de la région (Cyclades, Dodécanèse et Anatolie occidentale) montrent une évolution tectonique et thermique similaire depuis le Crétacé, marquée minéralogiquement par une succession d’épisodes de HP-BT puis de HT-BP. Toutefois, l’apport des données TRSCM et radiochronométriques (⁴⁰Ar-³⁹Ar, U-Pb) souligne un évènement thermique majeur contemporain à la mise en place du dôme métamorphique du Menderes. Cet événement que l’on explique par un changement drastique de la dynamique de subduction (i.e. déchirure du panneau plongeant sous le Massif du Menderes), se développe au Miocène. Des structures d’échelle crustale (i.e. détachements)accommodent la mise en place du Massif du Menderes et contrôlent la circulation des fluides dans la croûte, depuis la zone de transition fragile-ductile jusqu’à la surface, sans nécessairement impliquer la contribution de systèmes magmatiques dans la croûte supérieure. La Province géothermale du Menderes est considérée comme une province de haute température de taille mondiale car elle résulte de la dynamique de subduction qui contrôle spatialement et temporellement l’intensité de l’anomalie thermique mais également la mise en place de structures perméables(détachements) d’échelle crustale favorisant la circulation des fluides.

International audience; Most previous geodynamic studies treat subduction zones with backward migration (rollback), slab tearing or slab breakoff by numerical or laboratory experiments and by integrating seismicity, tomography data and geochemical studies. Here we investigate these processes in the Aegean-Anatolian domain and particularly the western side of Turkey (western Anatolia) by incorporating thermal regime of the crust, and in particular the geothermal fields as anomalies that could reflect the thermal state of Aegean subduction zone at depth. This domain is characterized by 1) extensional crustal deformation which progressively localized during the Aegean slab retreat from late Eocene to Present, enabling the development of a hot backarc domain; this extension accelerated between 15 and 8 Ma coeval with a fast rotation of the Hellenides and 2) since the latest Miocene, extension is coupled with the development of the North Anatolian Fault that accommodates the westward escape of the Anatolian block. Both the acceleration of extension in the Middle Miocene and the recent escape of Anatolia have been proposed to result from several slab tearing events, the first one being located below western Turkey and the Eastern Aegean Sea, a second one below eastern Turkey and a last one below the Corinth Rift (Faccenna et al., 2006; Jolivet et al., 2013). The distribution of magmatism and mineral resources has been suggested to be largely controlled by these retreat and tearing events (Menant et al., submitted). The development of a widespread active geothermal province in western Anatolia is unlikely to simply result from the Quaternary magmatism whose volcanism part has a too limited extent. Conversely, the long wavelength east-west variation of surface heat flow density could reflect deep thermal processes in the lower crust and/or deeper, and we thus look for possible connections with larger-scale mantle dynamics. We use the distribution of thermal anomalies at different scales and the 3D shape of the Aegean slab to discuss mantle and crustal dynamics. In order to constrain the development and the propagation of slab tears during subduction beneath western Anatolia, we used spatial and temporal data on magmatic activity, geochemical signatures of this activity (e.g. increase of mantle source component), seismic tomography models and seismicity data. We also discuss the origin of the thermal anomalies propagating all the way to the surface, whether they relate to deep-seated mantle processes only (western Anatolia, Turkey) or to more superficial volcanic processes above a hot mantle like in Central and Eastern Anatolia.

International audience; Strain localization is a fundamental process determining plate tectonics. It is expressed in the ductile field by shearzones where strain concentrates. Despite their worldwide distribution in most metamorphic units, their detailedcharacterization and processes comprehension are far to be fully addressed. In this work, a graphic approach totectono-metamorphic facies identification is applied to the Delfini Shear Zone in Syros (Cyclades, Greece), whichis mostly characterized by metabasites displaying different degree of retrogression from fresh eclogite to prasinite.Several exhumation mechanisms brought them from the depths of the subduction zone to the surface, fromsyn-orogenic exhumation to post-orogenic backarc extension. Boudinage, grain-size reduction and metamorphicreactions determinate strain localization across well-deformed volumes of rocks organized in a hierarchic frameof smaller individual shear zones (10-25 meters thick). The most representative of them can be subdivided in 5tectono-metamorphic (Tm) facies, TmA to E. TmA records HP witnesses and older folding stages preserved withinlarge boudins as large as 1-2 m across. TmB is characterized by much smaller and progressively more asymmetricboudins and sigmoids. TmC is defined by well-transposed sub- to plane-parallel blueschist textures crossed bychlorite-shear bands bounding the newly formed boudins. When strain increases (facies TmD-E), the texture isprogressively retrograded to LP-HT greenschist-facies conditions. Those observations allowed us to establish a sequenceof stages of strain localization. The first stage (1) is determined by quite symmetric folding and boudinage.In a second stage (2), grain-size reduction is associated with dense shear bands formation along previously formedglaucophane and quartz-rich veins. With progressively more localized strain, mode-I veins may arrange as tensiongashes that gradually evolve to blueschist shear bands. This process determinates the formation of smaller asymmetricsyn-blueschist boudins and is associated with epidote grain-size reduction, synonym of more intense strainlocalization. In the latest stage (3), newly formed chlorite-rich shear bands bound new boudins of the previouslyproduced terms having blueschist fine-grained heritage. Sense of shear is consistently top-to-the-ENE through theentire localization process. Greenschist-related boudinage is associated with quartz precipitation along the mainshear bands and at the necks of boudins, places of strain localization. Metamorphic reactions and transpositionsgradually obliterate the former texture, being progressively more active towards the top, where minor shear zoneshave been deforming at the expenses of similar folds and epidote-rich levels. The resulting qualitative analysismeans to be a proxy for further numerical models and a comparison to similar field-study areas.

International audience; Exhumation of metamorphic core complexes is accompanied by progressive strain localization within large-scale shear zones, which may evolve into long-lived bounding detachments affected by ductile to brittle deformation. Despite the well-studied P-T-t patterns of individual nappes, their relative timing, mode and kinematics of exhuma-tion are debated. In this study, in the frame of the Mediterranean syn-and post-orogenic deformation, examples of shear zone hierarchization and strain localization from Sifnos and Syros islands (Cyclades, Greece) are documented in detail in order to explain 3D-geometries and regional kinematics and are here tentatively related to the Ar/Ar ages available in literature. During the Eocene syn-orogenic uplift, the degree of strain localization increases progressively from blue-to green-schists deformation. Some of these shear zones where then reworked during the Oligo-Miocene post-orogenic deformation in different, usually warmer P-T conditions and a new episode of strain localisation, and an evolution toward brittle faulting, either along the main detachments or along newly created faults (as in Sifnos). Such shear zones demonstrate long-lived efficiency, especially where fluid circulation enhance retrograde metamorphic reactions. During Neogene, the final shape and exhumation of domes is the result of crustal thinning and brittle-ductile deformation in the whole Cycladic region. Although stretching directions along individual kilometric scale shear zones may be complex in the details, a simple general picture is shown for the Oligo-Miocene episode, less so for the Eocene one. Most Cycladic islands show a top-to-the-North sense of ductile shear from the syn-orogenic to the post-orogenic stage, this is the case of Sifnos for instance. The syn-orogenic stretching is however often more E-W trending, as exemplified by Syros and Tinos. The top-North or Top-East sense of shear is attributed to the NCDS for the post-orogenic stage and to a syn-orogenic detachment (Vari D.) for the syn-orogenic stage. However the southwestern Cyclades show clear top-South post-orogenic kine-matic indicators related to the WCDS, with a complete ductile to brittle evolution. As for the NCDS the WCDS leads to intense ductile deformation in its footwall. To the east of Serifos this ductile top-South sense of shear is lost. Only top-South brittle faults are found in Folegandros and Sifnos where they cut across the older foliation. The complexity of the distribution of shear sense on Syros and Sifnos, both in the ductile and brittle regimes, during the post-and syn-orogenic stages, is discussed in the framework of the transition in time from syn-orogenic exhumation faults to post-orogenic detachments and of the interactions between different sets of detachments, such as the NCDS and the WCDS.

International audience; 3D numerical modeling has been used to investigate how the variations of mechanical properties in sedimentary layered sections affect the development of normal faults. We calculated the distribution of the Coulomb stress to assess the proximity of the layers to failure through an elastic layered section. The simulation of various combinations of rock properties allowed us to compare the effect of the stiffness and strength contrasts, which promote or inhibit faulting in the stiff layer, respectively. For rock systems showing little variation in strength, nucleation of the fault occurs in the stiff layer (e.g., limestones orsandstones), whereas it occurs in the compliant layer (e.g., clay-rich rocks) if the stiff layer has a high cohesion. Considering a mean strength profile of the carbonate sequences, nucleation occurs in limestones if the ratio of Young’s moduli between the limestone and clay-rich rock is greater than 2; otherwise, clay-rich layers fail first. We also showed that nucleation is promoted in sandstones or limestones if these layers are thinner than the clayey layers. In a second set of simulation, using a slip on a fault, we examined the conditions needed to overcome the restriction of the fault propagation. Our results suggest that the lateral propagation of the fault, within a layer, produces increasingly favorable conditions for vertical propagation. A maximum aspect ratio of width to height of 13 is predicted for faults in limestone-clay sequences, and this maximum aspect ratio is expected to decrease as the contrast in the rock properties decreases.

International audience; The distribution of displacement along faults is a key parameter in various areas of geology such as earthquake studies, three-dimensional strain restoration, fault growth, and reservoir and seal strata relations in hydrocarbon systems. It is essential therefore to understand how local conditions govern displacement distribution. We analyse dip-parallel displacement profiles of normal faults cutting five alternating limestone and shale layers and we discuss their evolution, from their nucleation to their restriction by lithological interfaces or bed-parallel faults in clays, or to their further propagation through several layers. Local displacement gradients control the shape of displacement profiles and are highly variable over the course of fault history. Accordingly, the Dmax-L relation is nonlinear. Bed-parallel faults prove stronger restrictors than lithological interfaces and the correlation of the local gradient with lithology during restriction and propagation indicates that knowledge of these gradients is required if we are to understand how faults develop in multilayer systems.

International audience

The thesis is divided into two parts, the development of a conceptual framework for SRIS (Spatially Referenced Information Systems) adapted to different decision making settings and then wastewater treatment applications specifically designed for metal fabricating industries. I Development of a Conceptual Framework for SRIS The design of a SRIS in land-use planning is dependent upon the type of decision making context and a basic distinction is made between management, strategic planning, and negotiation purposes. It is ascertained that each one brings with it fundamentally different requirements with respect to the management of ambiguity and uncertainty. Once these concepts are presented together with the flexibility needed in the information treatment process, their implications are more fully expressed in terms of informational quality, bringing in such attributes as, on the one hand, accuracy, completeness, consistency, opportunity and comprehensiveness and, on the other hand, realism, interpretative ability, dialectical potential, projection and originality. Building upon these interactions between the decision context features and the information quality attributes, elements of a SRIS support guide are developed together with references to possible applications in order to highlight its relevance. II Wastewater Treatment Management and GIS Applications In this second part, a closer look at GIS applications is presented on the basis of real-life situations, examining in turn each one of the decision context types. The first GIS application is sketched out for management purposes. The Montréal Urban Community (MUC) is a public body faced with shared responsibility with respect to environmental quality, more specifically water quality management, and this can imply the need for a hierarchisation of overflows in its sewage system that will take into account industrial discharges. The thesis shows how a GIS can be used in dealing with potentially toxic overflows during thunderstorm events, by assessing their impacts on the environment. The second GIS application is settled in strategic planning terms. This time the MUC is faced with the problem of incomplete treatment of industrial effluent charges and several collective management options are analysed with respect to scale economies opportunities, transportation costs differentials and variable pollution risks. The thesis shows how operation research procedures coupled with GIS can support the decision making process. The last GIS application involves a negociation environment. The SIVO (Syndicat intercommunal de la Vallée de l'Ondaine) is a public institution located in part of the Loire River Basin, near Saint-Étienne in France, charged with the responsibility to conduct a negotiation process implying public and private organisations with respect to the management of industrial effluents. The SRIS is developed this time in a way that leads to convergence among a multiplicity of interests, starting with very diverse perceptions, values and objectives. A support system using role games, cooperative principles, multicriteria analysis and GIS capacities is developed in such a way as to help to bring consensus., En aménagement du territoire, les modalités de conception et d'utilisation d'un Système d'Information à Référence Spatiale (SIRS) dépendent du type de contexte décisionnel auquel il est intégré : la gestion, la planification stratégique ou la négociation. De ce fait, le SIRS doit témoigner, de manière appropriée, des besoins en gestion de l'incertitude et de l'ambiguïté caractéristiques d'un type de contexte décisionnel. D'une part, ces deux concepts sont illustrés par le niveaux requis de flexibilité du processus de traitement de l'information. D'autre part, ils s'expriment au travers de la qualité de l'information classiquement caractérisée par son exactitude, sa complétude, sa cohérence, son opportunité et son intelligibilité, mais aussi par son réalisme, son interprétation, sa dialectique, sa projection et son originalité. Nous proposons un guide d'aide à la pratique des SIRS issu du croisement entre les caractéristiques des contextes décisionnels retenus et les attributs relatifs à la qualité de l'information. Des applications SIG sont développées pour chaque type de contexte décisionnel afin de confronter la pertinence de ce guide avec ces études de cas. Une application SIG en question : un organisme chargé de la gestion du milieu récepteur souhaite hiérarchiser ses interventions de contrôle réglementaire auprès des établissements industriels. Il peut, à l'aide d'un SIG, simuler le trajet probable de déversements toxiques potentiels en temps d'orage afin de déterminer les risques localisés d'impact sur le milieu récepteur, de même que les sources potentielles de pollution industrielle. Une application SIG en planification stratégique : un organisme chargé de la planification du traitement des effluents industriels souhaite analyser la faisabilité d'options de gestion collective en tenant compte d'indicateurs d'économies d'échelle, de coûts de transport et de vulnérabilité au déversement. Le couplage d'un SIG avec une procédure opérationnelle composée de fonctions d'optimisation sous contraintes peut constituer un support d'aide à la décision. Une application SIG en négociation coopérative : un organisme animant un processus de négociation relatif à la gestion collective des effluents industriels souhaite stimuler le débat entre acteurs publics et privés aux perceptions, valeurs et intérêts différents. Il peut proposer une méthode d'aide à la négociation basée sur les principes du jeu de rôle et sur un couplage entre un SIG et une méthode d'analyse multi-critères dans le but de rechercher une combinaison "contextualisée" d'options individuelles et collectives d'assainissement industriel tout en respectant les règles d'une négociation coopérative.

Actes des journées Cassini 1998; International audience; Le GDR Cassini regroupe depuis 1992, des chercheurs en informatique et en géographie, dans le but de : - structurer la recherche en matière de SIG

Representative blue amphibole, phengite, epidote and chlorite chemical analyses from Leros, Greece

Representative blue amphibole, phengite, epidote and chlorite chemical analyses from Leros, Greece

The ability to generate deep flow in massive crystalline rocks is governed by the interconnectivity of the fracture network and its permeability which in turn is largely dependent on the in situ stress field. The increase of stress with depth reduces fracture aperture leading to a decrease in rock mass permeability. The frequency of natural fractures also decreases with depth resulting in less connectivity. The permeability of crystalline rocks is typically reduced to about 10-17 – 10-15 m2 at targeted depths for enhanced geothermal systems (EGS) applications that is >3 km. Therefore fluid injection methods are required to hydraulically fracture the rock and increase its permeability. In the mining sector fluid injection methods are being investigated to increase rock fragmentation and mitigate high stress hazards due to operations moving to unprecedented depths. Here as well detailed understanding of permeability and its enhancement is required. This paper reports findings from a series of hydromechanically coupled distinct element models developed in support of a hydraulic fracture experiment testing hypotheses related to enhanced permeability increased fragmentation and modified stress fields. Two principal injection designs are tested as follows: injection of a high flow rate through a narrow packed interval and injection of a low flow rate across a wider packed interval. Results show that the development of connected permeability is almost exclusively orthogonal to the minimum principal stress leading to strongly anisotropic flow. This is because of the stress transfer associated with opening of tensile fractures which increases the confining stress acting across neighboring natural fractures. This limits the hydraulic response of fractures and the capacity to create symmetric isotropic permeability relative to the injection wellbore. These findings suggest that the development of permeability at depth can be improved by targeting a set of fluid injections through smaller packed intervals instead of a single longer injection in open boreholes.

Mechanical heterogeneity of a sedimentary sequence exerts a primary control on the geometry of fault zones and the proportion of offset accommodated by folding. The Wildensbuch Fault Zone in the Swiss Molasse Basin, with a maximum throw of 40 m, intersects a Mesozoic section containing a thick (120 m) clay-dominated unit (Opalinus Clay) over- and underlain by more competent limestone units. Interpretation of a 3D seismic reflection survey indicates that the fault zone formed by upward propagation of an east–west-trending basement structure, through the Mesozoic section, in response to NE–SW Miocene extension. This configuration formed an array of left-stepping normal fault segments above and below the Opalinus Clay. In cross-section a broad monoclinal fold is observed in the Opalinus Clay. Folding, however, is not ubiquitous and occurs in the Opalinus Clay where fault segments above and below are oblique to one another; where they are parallel the fault passes through the Opalinus Clay with little folding. These observations demonstrate that, even in strongly heterogeneous sequences, here a four-fold difference in both Young9s modulus and cohesion between layers, the occurrence of folding may depend on the local relationship between fault geometry and applied stress field rather than rheological properties alone.

Normal faults often comprise arrays of fault segments. The boundaries between adjacent fault segments, relay zones and relay ramps can be of crucial importance to fluid migration pathways across and along faults and for across-fault reservoir juxtaposition. However, despite the increased number of studies of faults in high quality 3D seismic data, the three dimensional geometric or kinematic properties of relay zones or the controls on their 3D geometry are still unclear. This contribution investigates the characteristics of three dimensional segmentation based on an extensive collection of normal faults and relay zones in different geological settings. Our analysis shows that relay zones most often develop by bifurcation from a single fault surface but can also arise from the formation of segments which are disconnected in 3D from their inception. Relay zones generally occur between fault segments that step in the dip or strike direction, and intermediate oblique relay zones are less frequent. When combined together, these different geometries can form a complex spectrum of fault segmentation, whose characteristics can be related to underlying geological controls, such as the mechanical heterogeneity of the faulted sequence and the influence of the basement structure