Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The nucleation, propagation, and associated folding of ramp-flat-ramp normal faults were analyzed from field examples developed in a brittle/ductile multilayer sequence of the Huércal-Overa Basin (SE Spain). Gently dipping sandy silt layers, which display a low cohesive strength (C0 = 7 kPa, μ = 34°), favor the development of extensional detachments. A tectonic origin instead of a possible gravitational origin is supported by the perpendicularity between the paleoslope direction of the fluvial-deltaic environment inferred from imbricated pebbles, and the senses of movement deduced from fault slicken-lines. The link between high-angle normal faults (HANFs) --formed at different levels in the layered sequence-- with horizontal fault segments comes to develop ramp-flat-ramp normal faults with associated roll-over in the hanging wall. Observed extensional duplexes are formed by parallel detachments connected through synthetic Riedel faults. These Riedel faults would produce the back-rotation of the individual blocks (horses), i.e., extensional folding of the originally subhorizontal layers. There is no correlation between the analyzed ramp-flat-ramp normal faults, accommodating south-southeastward extension during Serravallian-lower Tortonian, and either the regional Alpujarride/Nevado-Filabride west-directed extensional shear zone or the top-to-the-north detachments within Alpujarride units, which are clearly sealed by Serravallian-lower Tortonian sediments. Therefore, the studied normal faults are restricted to the brittle/ductile multilayer fluvio/deltaic sequence and accommodate moderate late extension instead of belonging to a large crustal extensional system connected with a regional detachment at depth. Therefore, the basin formed in a moderate crustal thickness context where small and medium-scale extensional systems were subordinate structures. These natural examples support the development of low-angle normal faults at very shallow crustal levels in multilayer sequences with suitable rheological conditions.
ISSN: 0278-7407

hal-00750352
https://hal.archives-ouvertes.fr/hal-00750352
DOI : 10.1029/2012TC003130

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The reactivation of faults with near-optimal orientations is commonly considered to control the state of stress in the crust. Near the surface, where a principal stress direction is vertical, the attitude of such faults is explained by Anderson's theory. This raises the questions of how prevalent this type of faulting actually is in current seismicity, down to what depth it frequently occurs, and what range of friction angles explains it best. The Global Centroid Moment Tensor catalog is analyzed to address these questions. Dip-slip and strike-slip mechanisms are dominant, and oblique slips are relatively rare for well-constrained events with depths shallower than 30 km. Preferred Andersonian faulting is the simplest, but not the unique, explanation for this dominance. Isolating reverse, strike- slip, and normal events reveals an asymmetry in the distribution of nodal plane dips and plunges of the P, B, and T axes between reverse and normal faulting. Assuming that the most frequent events correspond to reactivation near optimal orientations yields 40-60 degrees and 0-20 degrees friction angles for reverse and normal faults, respectively. This indicates that reverse and normal faulting mechanics are not symmetrical with respect to stress configuration as predicted by Anderson's theory.
ISSN: 8755-1209

hal-00412159
https://hal.archives-ouvertes.fr/hal-00412159
DOI : 10.1029/2007RG000240

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : New-Caledonia island consists of an ultramafic nappe thrusted over a continental and arc-derived basement as the result of the closure of a back-arc basin during the upper Eocene. The morphology of New-Caledonia is mostly characterized by its elongated shape and rectilinear coastline. Indeed, the western and eastern edges of the island are delineated by N140 trending normal faults that are well imaged on seismic lines. Major tectonic lineaments onland, including the scarps corresponding to the main boundary of the ultramafic nappe, also trend N140 suggesting a morphotectonic control by faults having similar kinematics (longitudinal flexure-fault of previous authors). We provide detailed observations from some of these scarps demonstrating indeed that these are not erosional features in origin. We explore the possibility that such surfaces do represent major tectonic limits that accommodated extension and significant tectonic thinning of both the peridotite nappe and its basement. Remnants of a complex extensional fault zone, 200 m wide, are still preserved along the western scarp of the Mont Dore mountain, close to Noumea city. The deformed zone is composed of an early shallow dipping detachment fault, some decimeters thick, offset by a group of late high angle normal faults and is bounded by cataclastic breccias that progressively pass into the fractured host peridotite. The late high angle fault zones have been the site of important syn-tectonic fluid circulation and are underlined by cm-thick silica infills bearing vertical striae. Typical morphology of the main scarps with break of slope is related to the combination of high angle normal faults and low angle detachment. Similar shallow dipping detachment surfaces have been observed along the east coast of southern New-Caledonia as well as within the ultramafic nappe itself and its basement. This study confirms that N140 oriented, large fault zones, with pure-normal to transtensional component of displacement, controlled the morphotectonic evolution of New-Caledonia at the regional scale, after the obduction of ophiolite nappe at the end of the Eocene. Such a fact has to be taken into account when attempting to reconstruct the post-obduction evolution of the island and more particularly when considering the development and distribution of the Ni-rich lateritic surfaces.
EISSN: 1777-5817

hal-00411855
https://hal.archives-ouvertes.fr/hal-00411855
DOI : 10.2113/gssgfbull.179.3.315

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : International audience
In Eastern China, the North China Block (NCB) has experienced a complex tectonic evolution during Late Palaeozoic to Mesozoic times. The unconformable sedimentary cover, which ranges in age from Neoproterozoic to Permian, underwent two tectonic episodes in Early Triassic and Cretaceous times. An early north–south compressional phase, D1, characterized by north-verging recumbent folds with east–west-trending axes and top-to-the-north ductile shear zones can be observed in a gabbroic pluton and the Neoproterozoic sedimentary host rocks. The available radiometric ages allow us to interpret this event as an Early Triassic back-thrusting related to the final stage of the collision between the North China and South China Blocks. During the LateMesozoic, an extensional event characterized by (1) half-grabens filled by continental terrigeneous red beds and lava flows, (2) low-angle detachment faults, (3) synkinematic granitic plutons, and (4) metamorphic core complexes is widespread in the Eastern Liaoning Peninsula. This extensional D2 event can be subdivided into a ductile deformation and a brittle deformation, corresponding to different expressions of crustal deformation. In every area studied in the Eastern Liaoning Peninsula, the ductile D2 deformation is characterized by a NW–SE-trending stretching lineation with a top-to-the-NWsense of shear.Mica and amphibole fromthe metamorphic country rocks, granodioritic or monzogranitic plutons and their mylonitized margins yield 40Ar/39Ar ages ranging from 130 to 120 Ma. These dates support fast cooling and exhumation rates coeval with the extensional tectonics. The brittle D2 deformation is responsible for the formation of high-angle normal faults marked by low-temperature cataclasites bounding half-grabens. During the Mesozoic, the tectonic regime of Eastern China experienced a significant inversion from compression to extension. The Eastern Liaoning Peninsula massif provides an example of this geodynamic transition.
ISSN: 2041-4927

hal-00134055
https://hal-insu.archives-ouvertes.fr/hal-00134055
DOI : 10.1144/SP280.7

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
New magnetotelluric and receiver transfer function studies provide insights from the upper to the lower crust of the eastern Betic Cordillera, which is deformed by large folds, normal faults, and a major transcurrent left-lateral fault, the Carboneras Fault Zone (CFZ). Receiver function analysis determines a NNW dipping Moho reaching 20 degrees that increases in depth, from 20 km south of the CFZ up to 34 km in the Sierra de Los Filabres. In addition, seismic discontinuities determined in the upper crust are interpreted as major contacts between metamorphic complexes that are detached and folded. The MT inversion model reveals a conductive zone, also representing a crustal seismic discontinuity, associated with the Alpujarride/Nevado-Filabride contact and fitting the N vergent geometry of the Sierra Alhamilla antiform. A small flexure at Moho coincides with the CFZ, as revealed by the Bouguer anomaly trend, in agreement with the receiver function results. Moreover, the Bahr strike and tipper angle at the stations placed closest to the CFZ clearly reveal the continuity of the CFZ at least down to approximately 15 km in depth, crossing all the detected crustal discontinuities up to the Moho. The lack of a clear Moho offset associated with the Carboneras Fault supports the idea that some large strike-slip faults tend to accommodate the deformation by a broadening fault zone at lower crustal levels. Its nucleation could occur at the base of a thin crust, where melting processes critically reduced the lithospheric strength during the late Miocene, to then propagate upward, reaching the topographic surface. Northward, the lithosphere comprised moderately larger strength, and the crustal discontinuities favored the development of larger folds with kilometric amplitude instead of strike-slip faults since the late Miocene.
ISSN: 1525-2027

hal-00671024
https://hal.archives-ouvertes.fr/hal-00671024
DOI : 10.1029/2010GC003274

Éditeur(s) : HAL CCSD Geological Society
Résumé : International audience
We constrain the slip and cooling history of the Mykonos detachment footwall using thermochronometry. A U-Pb zircon age of 13.5 +/- 0.3 Ma dates intrusion of the Mykonos monzogranite. Ar-40/ Ar-39 homblende and biotite ages from the monzogranite are 12.7 +/- 0.6 Ma and 10.9 +/- 0.6 Ma, whereas zircon and apatite fission-track ages range from 13 +/- 0.8 Ma to 10.7 +/- 0.8 Ma and 12.5 +/- 2.2 Ma to 10.5 +/- 1.8 Ma. (U-Th)/He ages range from 13.6 +/- 0.6 Ma to 9.0 +/- 0.7 Ma for zircon and 11. +/- 10.5 Ma to 8.9 +/- 0.4 Ma for apatite. The ages in part overlap within 2 sigma errors and together with the long apatite fission-track lengths (>14 mu m) support rapid cooling at rates > 100 degrees C Ma(-1). The low-temperature thermochronometric ages decrease east-northeastwards in the direction of hanging-wall transport on the Mykonos detachment. Age-distance relationships show that the Mykonos detachment slipped at an average rate of 6.0 + 9.2/-2.4 km Ma(-1) c. 30 km of offset and c. 12 km of exhumation. This result indicates that Miocene low-angle normal faulting was not important for the exhumation of the Cycladic blueschist unit. The opening of the Aegean Sea basin in the Miocene was controlled by a few large-magnitude low-angle normal faults.
ISSN: 0016-7649

hal-00412177
https://hal.archives-ouvertes.fr/hal-00412177
DOI : 10.1144/0016-76492006-145

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The identification of the structures and deformation patterns in magma-poor continental rifted margins is essential to characterize the processes of continental lithosphere necking. Brittle faults, often termed mantle detachments, are believed to play an essential role in the rifting processes that lead to mantle exhumation. However, ductile shear zones in the deep crust and mantle are rarely identified and their mechanical role remains to be established. The western Betics (Southern Spain) provides an exceptional exposure of a strongly thinned continental lithosphere, formed in a supra-subduction setting during Oligocene-Lower Miocene. A full section of the entire crust and the upper part of the mantle is investigated. Variations in crustal thickness are used to quantify crustal stretching that may reach values larger than 2000% where the ductile crust almost disappear, defining a stage of hyper-stretching. Opposite senses of shear top-to-W and top-to-E are observed in two extensional shear zones located close to the crust-mantle boundary and along the brittle-ductile transition in the crust, respectively. At locations where the ductile crust almost disappears, concordant top-to-E-NE senses of shear are observed in both upper crust and serpentinized mantle. Late high-angle normal faults with ages of ca. 21 Ma or older (40Ar/39Ar on white mica) crosscut the previously hyper-stretched domain, involving both crust and mantle in tilted blocks. The western Betics exemplifies, probably better than any previous field example, the changes in deformation processes that accommodate the progressive necking of a continental lithosphere. Three successive steps can be identified: i/a mid-crustal shear zone and a crust-mantle shear zone, acting synchronously but with opposite senses of shear, accommodate ductile crust thinning and ascent of subcontinental mantle; ii/hyper-stretching localizes in the neck, leading to an almost disappearance of the ductile crust and bringing the upper crust in contact with the subcontinental mantle, each of them with their already acquired opposite senses of shear; and iii/high-angle normal faulting, cutting through the Moho, with related block tilting, ends the full exhumation of the mantle in the zone of localized stretching. The presence of a high strength sub-Moho mantle is responsible for the change in sense of shear with depth. Whereas mantle exhumation in the western Betics occurred in a backarc setting, this deformation pattern controlled by a high-strength layer at the top of the lithosphere mantle makes it directly comparable to most passive margins whose formation lead to mantle exhumation. This unique field analogue has therefore a strong potential for the seismic interpretation of the so-called “hyper-extended margins”.
ISSN: 0264-8172

insu-01310895
https://hal-insu.archives-ouvertes.fr/insu-01310895
https://hal-insu.archives-ouvertes.fr/insu-01310895/document
https://hal-insu.archives-ouvertes.fr/insu-01310895/file/Frasca-MarPetGeol-2016.pdf
DOI : 10.1016/j.marpetgeo.2016.04.020

Éditeur(s) : HAL CCSD
Résumé : This thesis has been conducted on a fractured crystalline basement located in Ploemeur (South of Brittany, France). The detailed study of this basement requires a good understanding of their internal structures, namely their intrinsic properties, flow mode, density and fractures distribution. This work is focused on the petrophysical characterization of the granitic formations. Physical properties were determined from downhole geophysical measurements and images, and petrophysical measurements with thin sections made for each mini-core in the laboratory. Fresh-altered schist and fresh-altered granite separated by a normal angle fault are the main lithology of the Ploemeur crystalline basement. The results showed that the petrophysical properties were function of both porosity variation and degree of alteration and that the pore-space topology was found to be porositydependent. This thesis introduces a new formula between electrical resistivity and porosity. In addition, the laboratory measurements of Ploemeur revealed that seismic wave velocity was a function not only of porosity, but also of the predominant pore type. In general, the pore aspect ratio inverted from velocity measurements were classified roughly into crack shape. In the Ploemeur crystalline basement, the downhole geophysical measurements and images were used to measure changes in physical and chemical properties in the borehole fluid and the bedrock surrounding the boreholes. The effective integration of different geophysical methods, hydrogeological tests and lithological description was the best way to characterize the fractures in the crystalline basement, and is critical for a suitable estimation of fluid circulation.
Le socle cristallin fracturé, situé à Ploemeur (Bretagne sud, France) est l'objet de ce travail de thèse. L'étude détaillée du socle nécessite une bonne compréhension de la structure interne, à savoir les propriétés intrinsèques, le mode d'écoulement, la densité et la distribution des fractures. Ce travail de thèse est consacré à la caractérisation pétrophysique des formations granitiques. Les propriétés physiques ont été déterminées à partir de l'interprétation des données de mesures de géophysique en forage, des images de paroi du puits et des mesures pétrophysiques réalisées sur carottes en laboratoire. Afin de replacer les mesures dans leur contexte lithologique, une lame mince a été analysée pour chaque mini-carotte. Les formations lithologiques rencontrées dans le socle cristallin de Ploemeur sont des schistes et granites sains et altérés, ces deux lithologies étant séparées par une zone de faille. Les résultats ont montré que les propriétés pétrophysiques des roches étaient fonction à la fois de la variation de la porosité et du degré d'altération des roches et que la topologie de l'espace poreux était fortement dépendante de la porosité. Cette thèse introduit une nouvelle formule entre la résistivité électrique et la porosité. De plus, les mesures en laboratoire sur les échantillons de Ploemeur révèlent que les vitesses sismiques ne sont pas seulement fonction de la quantité de porosité, mais aussi fonction de facteur de forme. Ce dernier a été calculé sur les échantillons du socle de Ploemeur à partir des vitesses acoustiques. Les résultats ont montré que la porosité est de forme fissurale. L'intégration des données issues des images optiques et acoustiques, des mesures de géophysique en forage, et de la description des carottes a permis d'étudier de façon détaillée la géologie et l'hydrodynamique du socle de Ploemeur. L'intégration effective de ces différentes méthodes avec les tests hydrogéologiques ressort comme la meilleure façon de caractériser les fractures et les circulations en eau dans le socle.
https://tel.archives-ouvertes.fr/tel-00444175

Droits : info:eu-repo/semantics/OpenAccess
tel-00444175
https://tel.archives-ouvertes.fr/tel-00444175
https://tel.archives-ouvertes.fr/tel-00444175/document
https://tel.archives-ouvertes.fr/tel-00444175/file/thesebelghoul.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The western margin of the Gulf of Mexico (Veracruz State, Mexico) displays an extensive Neogene gravitational system, whereby the Neogene siliciclastic sediments are detached from underlying Mesozoic carbonates along decollement surface in Oligocene underpressured clays. Rapidly subsiding half-grabens develop above the footwall associated with major listric faults, whereas mini-basins develop in the deepest parts of the slope, in conjunction with the growth of west-verging compressional features. Between the high-angle normal faults in the west and the thrust anticlines in the east, a wide roll-over structure has grown progressively, resulting in a major topographic break in the morphology of the slope profile. Coupled forward kinematic modelling (Thrustpack) and stratigraphic modelling (Dionisos), calibrated against seismic profiles and two key nearshore wells, have been applied to representative regional transects across the margin, in order to quantify the vertical (subsidence) and horizontal (gravitational) deformations, and to discuss the impact of various key parameters on the distribution of debris flow depositions. These simulations are compared with data from distant ODP wells and discussed in the scope of current exploration strategies in both the US and Mexican portions of the Gulf of Mexico basin.
ISSN: 0040-1951

hal-00424595
https://hal.archives-ouvertes.fr/hal-00424595
DOI : 10.1016/j.tecto.2008.06.017