Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In the framework of the Africa-Europe convergence, the Mediterranean system presents a complex interaction between subduction rollback and upper-plate deformation during the Tertiary. The western end of the system shows a narrow arcuate geometry across the Gibraltar arc, the Betic-Rif belt, in which the relationship between slab dynamics and surface tectonics is not well understood. The present study focuses on the Western Betics, which is characterized by two major thrusts: 1/ the Internal/External Zone Boundary limits the metamorphic domain (Alboran Domain) from the fold-and-thrust belts in the External Zone; 2/ the Ronda Peridotites Thrust allows the juxtaposition of a strongly attenuated lithosphere section with large bodies of sub-continental mantle rocks on top of upper crustal rocks. New structural data show that two major E-W strike-slip corridors played a major role in the deformation pattern of the Alboran Domain, in which E-W dextral strike-slip faults, N60 thrusts and N140 normal faults developed simultaneously during dextral strike-slip simple shear. Olistostromic sediments of Lower Miocene age were deposited and deformed in this tectonic context and hence provide an age estimate for the inferred continuous westward translation of the Alboran Domain that is accommodated by an E-W lateral (strike-slip) ramp and a N60 frontal thrust. The crustal emplacement of large bodies of sub-continental mantle may occur at the onset of this westward thrusting in the Western Alboran domain. At lithosphere-scale, we interpret the observed deformation pattern as the subduction upper-plate expression of a lateral slab tear and its westward propagation since Lower Miocene.
ISSN: 0040-1951

insu-01163695
https://hal-insu.archives-ouvertes.fr/insu-01163695
https://hal-insu.archives-ouvertes.fr/insu-01163695/document
https://hal-insu.archives-ouvertes.fr/insu-01163695/file/Frasca-2015.pdf
DOI : 10.1016/j.tecto.2015.05.017

Éditeur(s) : HAL CCSD
Résumé : International audience
In the frame of the Africa-Europe convergence, the Mediterranean tectonic system presents a complex interaction between subduction rollback and upper-plate deformation during the Tertiary. The western Mediterranean is characterized by the exhumation of the largest subcontinental mantle massif worldwide (the Ronda Peridotite) and a narrow arcuate geometryacross the Gibraltar arc within the Betic-Rif belt (the internal part being called the Alboran domain), where the relationship between slab dynamics and surface tectonics is not well understood. New structural and geochronological data are used to argue for 1/ hyperstrechting of the continental lithosphere allowing extensional mantle exhumation to shallow depths, followed by 2/ lower miocene thrusting. Two Lower Miocene E-W-trending strike-slip corridors played a major role in the deformation pattern of the Alboran Domain, in which E-W dextral strike-slip faults, N60°-trending thrusts and N140°-trending normal faults developed simultaneously during dextral strike-slip simple shear. The inferred continuous westward translation of the Alboran Domain is accommodated by a major E-W-trending lateral ramp (strike-slip) and a N60°-trending frontal thrust. At lithosphere-scale, we interpret the observed deformation pattern as the upper-plate expression of a lateral slab tear and of its westward propagation since Lower Miocene. The crustal emplacement of the Ronda Peridotites occurred at the onset of this westward motion.The Miocene tectonics of the western Alboran is therefore marked by the inversion of a continental rift, triggered by shortening of the upper continental plate and accommodated by E-W dextral strike-slip corridors. During thrusting and westward displacement of the Alboran domain with respect to Iberia, the hot upper plate, which involved the previously exhumed sub-continental mantle, underwent fast cooling.
AGU Fall Meeting 2015
San Francisco, United States

insu-01242043
https://hal-insu.archives-ouvertes.fr/insu-01242043

Éditeur(s) : HAL CCSD Société Géologique de France
Résumé : International audience
The seaward extension of onshore formations and structures were previously almost unknown in Provence. The interpretation of 2D high-resolution marine seismic profiles together with the integration of sea-bottom rock samples provides new insights into the stratigraphic, structural and paleogeographic framework of pre-Messinian Salinity Crisis (MSC) deposits of the Provence continental shelf. Seven post-Jurassic seismic units have been identified on seismic profiles, mapped throughout the offshore Provence area and correlated with the onshore series. The studied marine surface and sub-surface database provided new insights into the mid and late Cretaceous paleogeography and structural framework as well as into the syn-and post-rift deformation in Provence. Thick (up to 2000 m) Aptian-Albian series whose deposition is controlled by E-W-trending faults are evidenced offshore. The occurrence and location of the Upper Cretaceous South-Provence basin is confirmed by the thick (up to 1500 m) basinal series downlaping the Aptian-Albian unit. This basin was fed in terrigenous sediments by a southern massif (" Massif Méridional ") whose present-day relict is the Paleozoic basement and its sedimentary cover from the Sicié imbricate. In the bay of Marseille, thick syn-rift (Rupelian to Aquitanian) deposition occurred (>1000 m). During the rifting phase, syn-sedimentary deformations consist of dominant N040 to N060 sub-vertical faults with a normal component and N050 drag-synclines and anticlines. The syn-rift and early post-rift units (Rupelian to early Burdigalian) are deformed and form a set of E-W-trending en echelon folds that may result from sinistral strike-slip reactivation of N040 to N060 normal faults during a N-S com-pressive phase of early-to-mid Burdigalian age (18-20 Ma). Finally, minor fault reactivation and local folding affect post-rift deposits within a N160-trending corridor localized south of La Couronne, and could result from a later, post-Burdigalian and pre-Pliocene compressive phase.
Cadre tectonostratigraphique des formations anté-pliocènes du plateau continental de Provence (golfe du Lion oriental, SE France) Mots-clés. – Géologie marine, Tectonostratigraphie, Stratigraphie sismique, Paléogéographie crétacée, Rifting oligo-miocène, Compression post-rift Résumé. – Le prolongement en mer des formations et des structures provençales était jusqu'alors largement inconnu.L'interprétation de profils de sismique-réflexion marine 2D et l'intégration de dragages et carottages du fond-marin ont permis d'apporter des éléments nouveaux concernant le cadre stratigraphique, structural et paléogéographique des dé-pôts anté-Messiniens du plateau continental de Provence. Sept unités sismiques post-jurassiques ont été identifiées sur les profils sismiques, cartographiées à travers le plateau continental et corrélées avec les séries affleurant à terre. Une épaisse unité apto-albienne (jusqu'à 2000 m) dont le dépôt est contrôlé par des failles E-W a été mise en évidence en mer. L'existence d'un bassin subsident au Crétacé supérieur sur le plateau continental de Provence a été confirmée par le développement d'une épaisse série de bassin (jusqu'à 1500 m) reposant en downlap sur l'Apto-Albien. Le socle mé-tamorphique de l'écaille de Sicié et sa couverture sédimentaire peut être considéré comme une relique allochtone du « Massif Méridional » ayant alimenté le Bassin sud-provençal en éléments terrigènes au Crétacé supérieur. Dans la rade de Marseille, une épaisse unité syn-rift (Rupélien à Aquitanien) a été mise en évidence (>1000 m), structurée en une série de synformes en échelon d'axe E-W et affectée par des failles d'orientation dominante N040 à N060. Sur le flanc sud des synformes, la formation de plis d'axe N050 est associée à une déformation syn-sédimentaire. La formation des synformes en échelon d'axe E-W résulterait d'une réactivation en décrochement des failles N040 à N060 pendant une phase de compression N-S dont l'âge est compris entre le Burdigalien inférieur et moyen (18-20 Ma). Enfin, les dépôts post-rift sont affectés par des déformations mineures (réactivation de failles et plis associés), le long d'un couloir d'orientation N160 à l'ouest de la baie de Marseille, attribuables à une phase de compression post-burdigalienne et anté-pliocène.
ISSN: 0037-9409

hal-01463727
https://hal-amu.archives-ouvertes.fr/hal-01463727
https://hal-amu.archives-ouvertes.fr/hal-01463727/document
https://hal-amu.archives-ouvertes.fr/hal-01463727/file/Fournier_et_al_Provence_2016.pdf
DOI : 10.2113/gssgfbull.187.4-5.187

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
New U–Pb monazite, zircon, and xenotime ages date the Late Carboniferous crystallization of the anatectic Vialais granite in the Montagne Noire Axial Zone and the high-temperature deformation and metamorphism of the augen gneiss (Ordovician granite protolith) from which the granite was likely derived. The U–Pb monazite ages obtained from the augen gneiss (308 ± 3 Ma), late kinematic Vialais granite (303 ± 4 Ma), and post-kinematic leucogranite (298 ± 2 Ma), bracket the high-temperature deformation and metamorphism at ~ 310–300 Ma, clearly postdating regional contraction and nappe emplacement (> 320 Ma). The planar–linear and locally linear fabrics in the augen gneiss outline a regional-scale double dome structure (Caroux and Espinouse sub-domes) containing smaller (km-scale) upright folds. Compared to the Caroux sub-dome, the larger, migmatitic Espinouse sub-dome contains abundant leucosome, leucogranite bodies and late-kinematic intrusions (Vialais granite). The Vialais granite displays a weak magmatic foliation that defines the main layering of the Espinouse migmatite. Ellipsoidal quartz–sillimanite nodules concentrated above the roof of the granite recorded an increment of strain (vertical shortening, E–NE elongation) during granite emplacement and crystallization, consistent with the extension event that exhumed the domes. These new geochronological and structural data suggest that the Montagne Noire double dome formed in a pull-apart structure within a dextral strike–slip system. Upright folding in the sub-domes has been traditionally assigned to a regional contraction event; alternatively, we propose that local contraction is associated with the convergence of low-viscosity crust beneath the upper crust pull-apart. Dynamic models of extension of hot crust indicate that contraction at depth is generated by flow of low-viscosity orogenic crust converging and rising to fill the gap created by upper crust extension. This interpretation solves the long-standing problem of apparent coeval contraction and extension in the Montagne Noire double dome and establishes migmatite dome emplacement in strike–slip corridors as a style of late Variscan tectonics.
ISSN: 0040-1951

insu-01112009
https://hal-insu.archives-ouvertes.fr/insu-01112009
DOI : 10.1016/j.tecto.2014.12.002

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
We use digital elevation models and satellite imagery data completed with field observations to develop an integrated morphotectonic analysis of the anomalous topography of the Central Cordillera of Patagonia between 46 degrees S and 48 degrees S, in a region overlying subducted segments of the Chile Spreading Ridge. This region shows a number of peculiar features, not expected in a normal subduction-related belt located away from a buried spreading center. First, it is characterized by overall short-wavelength topography and highly contrasted reliefs, typical of deeply incised young mountain belts, but surprisingly, also by an average very low elevation of similar to 900 m. Second, the Cordillera lacks central high reliefs; instead, there is a central, depressed domain with average low slope gradients including the deepest point of the study area (300 m below sea level in the bottom of Lake General Carrera/Buenos Aires). This depressed area is flanked by western and eastern regions of higher elevation having opposite general slope dips. To the east, the central Patagonian Cordillera is now separated from the flat plains of the Pampean domain (representing its former piedmont) and several elevated basaltic plateaus (mesetas) by 160 degrees N-180 degrees N trending morphotectonic corridors and the western border scarps of the mesetas. These scarps correspond to neotectonic features controlled by recent vertical faults, mostly active after 3 Ma. Remnants of a former peneplain, the Avellanos surface, are widespread within the entire Cordilleran region. From geological evidence, this peneplain formed between 15 and 4 Ma and was connected originally with the mesetas domain and now is dissected by these corridors. It is shown that a negative inversion related to extensional and strike-slip faulting occurred in the frontal region of the Cordillera at 3 Ma synchronously with the emplacement of magmatic products. Timing of the extensional deformation in central Patagonia is concomitant with the migration at depth of different segments of the South Chile Ridge, which entered the trench at 6 and 3 Ma, respectively, and the consequent opening of a slab window allows asthenospheric hot mantle to reach lithospheric regions. Finally, migration of segments of the Chile Spreading Ridge since 6 Ma triggered regional uplift of the Cordillera followed by limited extension in relation with increased thermal weakening of the crust.
ISSN: 0278-7407

hal-00486334
https://hal.archives-ouvertes.fr/hal-00486334
DOI : 10.1029/2009TC002453

Éditeur(s) : HAL CCSD
Résumé : International audience
Tin mineralization in Achmmach deposit (NE of Moroccan Central Massif) is associated with tourmaline-rich alteration halos and faults, within N70 shear zones, hosted in sandstones and metapelites of the Upper Visean-Namurian. Such deposits were reported as late-Variscan in age and related to the emplacement of late orogenic granite not outcropping in the studied area.From field constraints, it appears that the late Variscan phase is marked by a transition from transpression to extension with conditions of deformation evolving from ductile to brittle environments. During the transpressive phase (horizontal shortening direction roughly trending E-W), pervasive tourmaline is deposited under the form of metasomatic halos around fractures in the upper levels relative to the deep batholith. This hydrothermal activity is coeval with ductile shear zones within a large corridors trending N70. Tourmaline-rich alteration appears as a hardening stage contributing to the modification of the tectonic style of rocks. Thereafter, a strong brecciation occurs in response of re-using and re-opening of the strike-slip structure. The result is (1) the formation of dextral (N070, N020) and sinistral (N120) shears, and (2) the circulation of fluids within early tourmalinites and formation of tourmaline-rich breccia. Subsequently, during the late orogenic extensional phase, tourmalinite breccias reopened as normal faults acting as overpressure fluid pathways for developing other breccias and veins. Such event is marked by deposition of tin mineralization i.e., cassiterite followed by sulphides, and then fluorite and carbonates at the end.From analysis of the shear-zone structure and superimposition of tourmalines and tin mineralization in the same structures, it is possible to suggest a structural control continuum. Such control is well expressed during metasomatism and deposition of hydrothermal tourmaline under the transpressive phase. Thereafter, under the extensive phase allowing open-space, tin-mineralization were trapped.This study has been supported by AI MA/09/210
24ème RST
Pau, France

insu-01546927
https://hal-insu.archives-ouvertes.fr/insu-01546927