Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The emergent domain known as “Kasserine Island” in central Tunisia, to the West of the North–South Axis, was emerging during the Turonian. This area has undergone several changes during the Cretaceous–Eocene period. In the present study, the compilation of surface and sub-surface data provided new information about the boundaries variations of the emerged domain. The analysis of paleogeographic maps allowed the identification of three distinct stages of evolution. The first stage extents from the Middle Turonian to the Lower Maastrichtian where the emergent domain covers the area extending from Jebels Selloum-Sidi Aich in the West to Jebel Bouhedma in the East. The boundaries of this area coincide with the E–W Kasserine fault to the North, the N–S Lessouda-Boudinar fault in the East and the N 120 el Mech-Souinia flexure at the South. This emersion contemporaneous with a high eustatic level is most likely related to tectonic activity. The extensional tectonic regime that is characterized by a NE–SW minimal horizontal stress, has reactivated border faults with a normal component. The interference of the tilting of these border faults was at the origin of the emergence of this domain. The ascent of the Triassic salt may also have contributed in this uplift.In the second stage, the emerged domain has reached its maximum expansion to the North, the West and the South during the Middle Maastrichtian–Paleocene period. Its northern limit is irregular, while the southern limit coincides with the N120 Gafsa fault and the E–W fault of Jebels Orbata-Bouhedma. The N–S Lessouda-Boudinar fault forms the eastern limit. This expansion is mostly related to the global eustatic fall that is well characterized during this period, and partly to the compressive tectonic activity.The Lower Eocene is characterized by a marine transgression that has interested the northern edge of the Island, where the Ypresian deposits are discordant on older series. This edge was irregular and marked by the Gulf of Sbiba. The eastern, the southern, and the western boundaries kept the same shape as that of the previous stage. The compressive tectonic regime, characterized by a NW–SE maximum horizontal stress, is accentuated. This constraint state has generated NE–SW folds and NW–SE grabens. Some of these structures allowed the accumulation of a thick phosphate deposits at their edges, and continental deposits in the emerged area.During the Middle to Upper Eocene, the emergent area narrowed further at the North. The deposits are transgressive and discordant on older series. The Other limits always coincide with the Gafsa fault, the Jebels Orbata-Bouhedma and Jebels Lessouda-Boudinar faults. This period is characterized by the filling of the Gafsa basin by evaporate deposits before its emergence in the Oligocene. As a result, the southern-central Tunisia emerged as one area.
ISSN: 0899-5362

hal-01243490
https://hal.archives-ouvertes.fr/hal-01243490
DOI : 10.1016/j.jafrearsci.2015.07.027

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Miradouro da Lua cliffs, which are 60 km south of Luanda, record the building and uplift of the late Neogene Palaeo-Cuanza delta. The detailed study of the sedimentary architecture and stacking pattern permitted separation of the pile into five depositional units bounded by erosional surfaces and characterised by separate facies associations (genetic sequences = units in this paper). At the base of the series, aeolian deposits (Unit 1) mark the development of a possible coastal desert during the late Miocene aridification. The major Pliocene sea-level rise (Transgressive Systems Tract) led to the drowning of the continental platform into a discrete shoreface-foreshore sequence (Unit 2), followed by an expanded deltaic sequence (Unit 3) that represents the main outcrop of the area. The sedimentary fabric of this prograding wedge during the Highstand Systems Tract reveals laterally stacked pluri-hectometic mouth bars built by the abrupt switching of a bird-foot delta during the Pliocene highstand. The clinoforms are deeply incised by submarine gullies filled both by periodic river-driven turbidite and tidal currents (Unit 4) during the coeval growing of the delta. The topset of the prograding wedge and associated gullies infill is truncated by an overall erosional unconformity that marks the widespread development of an extensive braid-delta system (Unit 5) during the lower Pleistocene sea-level drop (Lowstand Systems Tract). The last 6 m of the Braid-delta unit is overprinted by a ferallitic profile, forming the surface of the plateau and indicating long-term subaerial exposure and weathering processes consistent with the maximum warming of the middle to late Pleistocene interglacial periods. The successive abrupt shifts of the depositional systems through the sedimentary pile indicate a high-amplitude sea level amplified by major coastal uplifts and the reorganisation of the fluvial network. In this context, the palaeo-Cuanza prograding wedge signals the westward tilting and 60 m total uplift of the coastal plain during the Pliocene. A new uplift pulse by differential tilt and slope increase is deduced from the widespread development of the braid-delta complex during the early Pleistocene. The last tectonic event corresponds to the 80- to 100-m uplift and ferallitic paedogenesis during the middle to late Pleistocene interglacial stages.
ISSN: 0899-5362

hal-01053716
https://hal.archives-ouvertes.fr/hal-01053716
DOI : 10.1016/j.jafrearsci.2014.01.013

Éditeur(s) : HAL CCSD Geological Society of America
Résumé : In Gobi Altay and Altay, Mongolia, several flat surfaces, worn through basement rocks and uplifted during the ongoing tectonic episode to a similar altitude of 4000 m, suggests disruption of a single large-scale surface. New thermochronology and field data show that the plateau surfaces represent uplifted parts of an ancient peneplain that formed during Jurassic time. The Gobi Altay and Altay flattopped massifs are tectonically and geomorphologically unique. Their preservation for ~150 m.y. implies that no further tectonic movements occurred before the onset of the last deformation episode, 5 ± 3 m.y. ago. It also suggests that very low erosion rates were maintained by a dry climate over millions of years.
ISSN: 0091-7613

hal-00406436
https://hal.archives-ouvertes.fr/hal-00406436
DOI : 10.1130/G23758A.1

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
At the North-Ecuadorian convergent margin (1°S–1.5°N), the subduction of the rough Nazca oceanic plate leads to tectonic erosion of the upper plate and complex seismogenic behavior of the megathrust. We used three selected pre-stack depth migrated, multi-channel seismic reflection lines collected during the SISTEUR cruise to investigate the margin structure and decipher the impact of the subducted Atacames seamounts on tectonic erosion, interseismic coupling, and seismogenesis in the region of the 1942 Mw7.8 earthquake.This dataset highlights a subducted ∼30×40 km∼30×40 km, double-peak seamount that belongs to the Atacames seamount chain and that is associated with a deep morphologic re-entrant containing mass transport deposits.The seamount subduction uplifted the margin basement by ∼1.6 km and pervasively broke the margin by deep and intense reverse faulting ahead of the seamount, a process that is likely to weaken considerably the margin. In the seamount wake, the basement reverse fault system rotated counter-clockwise. This faulted basement is overlain with slope sediment sliding along listric normal faults that sole out onto the BSR. This superposition of deep tectonic contraction within the basement and shallow gravitational extension deformation within the sediment highlights the key role of gas hydrate on outer slope erosion.In addition to long-term regional basal erosion, the margin basement has thinned locally by an extra 0.8–1 km in response to the subduction of the Atacames seamount chain and hydrofracturing by overpressured fluids at the margin toe. This pervasively and deeply fractured margin segment is associated with a seismically quiet and GPS-modeled low interseismic coupling corridor that terminates downdip near the 1942 epicenter and locked zone. We suggest that the deeply buried double-peak Atacames seamount triggered the 1942 earthquake ahead of its leading flank. This result supports previous studies proposing that subducted seamounts provide unfavorable conditions for locking the updip segment of the plate boundary limiting the updip extent of seismogenic zones, but may favor large subduction earthquakes at greater depths.
ISSN: 0012-821X

hal-01256399
https://hal.archives-ouvertes.fr/hal-01256399
DOI : 10.1016/j.epsl.2015.10.043

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In fold and thrust belts drainage organization and patterns of sedimentation depend conceptually on the ability or not for preexisting reaches to incise uplifting thrust sheets. In this study we investigate experimentally the dynamics of drainage network in a wedge submitted to shortening and erosion. It allows us to reproduce and to monitor the interactions between tectonics, erosion and sedimentation during the development of up to five successive thrust sheets. In the experiments channels adjust to uplift rate by both increasing their slope and narrowing their channels as it is observed in nature. The series of experiments shows that the proportion of persistent preexisting transverse channels increases with the ratio of rainfall over shortening rates. The experiments confirm the view that the competition between discharge and tectonic uplift controls along-strike variations in sediment flux in sedimentary basins by controlling the drainage organization. If the transverse channels draining a wedge are not diverted, a line-source dispersal system develops in front of the active structure. If channels are diverted in the backlimb of the frontal structure it results in point-sourced depositional systems separated by areas fed only by small channels developing in the front of the wedge. Fans accumulated in front of the active structures reveal two stages of sedimentation, one of progradation, while the frontal structure is active and a second one of valley backfilling and thrust sealing during internal deformation of the wedge. The experiments also suggest that spatial variations in rock uplift rate along a thrust front may be evidenced by minimum-discharge variations of persistent transverse channels.
ISSN: 0040-1951

insu-01252482
https://hal-insu.archives-ouvertes.fr/insu-01252482
DOI : 10.1016/j.tecto.2015.09.007

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Located on the margin of the west Alboran basin, the Gibraltar Arc (Betic-Rif mountain belt) displays post-Pliocene vertical movements evidenced by uplifted marine sedimentary basins and marine terraces. Quantification of vertical movements is an important clue to understand the origin of present-day relief generation in the Betic-Rif mountain chain together with the causes of the Messinian Salinity Crisis. In this paper, we present the results of a pluridisciplinary study combining an analysis of low temperature thermochronology and Pliocene basins evolution to constrain the exhumation history and surface uplift of internals units of the Rif belt (Northern Morocco). The mean (U-Th)/He apatite ages obtained from 11 samples are comprised between 14.1 and 17.8 Ma and display a wide dispersion, which could be explained by a great variability of apatite chemistries in the analyzed samples. No correlations between altitude and age have been found along altitudinal profile suggesting a rapid exhumation during this period. Thermal modeling using our (U-Th)/He apatite ages and geochronological data previously obtained in the same area (40Ar/39Ar and K/Ar data on biotite, zircon and apatite fission track) allow us to propose a cooling history. The rocks suffered a rapid cooling at 60-100 °C/Ma between 22.5 and 19 Ma, then cooled to temperatures around 40 °C between 19 and 18 Ma. They were re-heated at around 110 °C between 18 and 15 Ma then rapidly cooled and exhumed to reach the surface temperature at around 13 Ma. The re-heating could be related to a renewal in thrusting and burying of the inner zones. Between 15 and 13 Ma the cooling resumed at a rate of 50 °C/Ma indicating an exhumation rate of 0.8 mm/y considering an average 40 °C/km geothermal gradient. This exhumation may be linked to the extension in the Alboran Sea. Otherwise biostratigraphic and sedimentological analysis of Pliocene basins of the internal Rif provided informations on the more recent events and vertical movements. Pliocene deposits of the Rifian coast represent the passive infilling of palaeo-rias between 5.33 and 3.8 Ma. The whole coastal area was uplifted at slow average rates (0.01-0.03 mm/y) in relation with a northeastward tilting of 0.2-0.3° since the Lower-Pliocene. A late Pliocene to present extensional tectonics associated to uplift has been identified all along the coastal ranges of the Internal Zone of the Rif chain. This extension was coeval with the major late Pliocene to Pleistocene extensional episode of the Alboran Sea and appears to be still active nowadays. No significant late Messinian uplift was evidenced, thus calling into question the geodynamic models relating the closure of the marine gateways and the MSC to slab roll back.
ISSN: 0264-3707

hal-01053531
https://hal.archives-ouvertes.fr/hal-01053531
DOI : 10.1016/j.jog.2014.01.006

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study analyzes the active tectonics within the northwestern and southeastern extensions of the Pambak-Sevan-Syunik fault (PSSF), a major right-lateral strike-slip fault cutting through Armenia. Quantifying the deformations in terms of geometry, kinematics, slip rates and earthquake activity, using cosmogenic 3He, OSL/IRSL and radiocarbon dating techniques, reveal different behaviors between the two regions. Within the northwestern extension, in the region of Amasia, the PSSF bends to the west and splits into two main WNW–ESE trending reverse faults defining a compressional pop-up structure. We estimate an uplift rate and a shortening rate of 0.5 ± 0.1 mm/y and 1.4 ± 0.6 mm/y, respectively. This suggests that most of the ∼2 mm/y right lateral movement of the PSSF seems to be absorbed within the Amasia pop-structure. Within the southeastern extension, the PSSF shows signs of dying out within the Tsghuk Volcano region at the southernmost tip of the Syunik graben. There, the tectonic activity is characterized by a very slow NS trending normal faulting associated with a slight right-lateral movement. Slip rates analyses (i.e. vertical slip rate, EW stretching rate at 90° to the fault, and right-lateral slip rate of ∼0.2 mm/y, ∼0.1 mm/y and ∼0.05 mm/y, respectively) lead to the conclusion that the right lateral movement observed further north along the PSSF is mainly transferred within other active faults further west within the Karabagh (Hagari fault or other structures further northwestwards). Comparing our slip rates with those estimated from GPS data suggests that most of the deformation is localized and seismic, at least within the Tsghuk region. The geometrical and kinematic pattern observed within the two terminations of the PSSF suggests that the fault and its surrounding crustal blocks are presently rotating anticlockwise, as also observed within the GPS velocity field. This is consistent with the recent kinematic models proposed for the Caucasus-Kura-South Caspian region and brings a new insight into the present geodynamics of Armenia.
ISSN: 1040-6182

hal-01307342
https://hal.archives-ouvertes.fr/hal-01307342
DOI : 10.1016/j.quaint.2015.05.021

Éditeur(s) : HAL CCSD Elsevier
Résumé : The Erro-Tobbio peridotites (Voltri Massif, Ligurian Alps) represent subcontinental lithospheric mantle tectonically exhumed during Permo-Mesozoic extension of the Europe-Adria lithosphere. Previous studies have shown that exhumation started during Permian times, and occurred along kilometer-scale lithospheric shear zones which enhanced progressive deformation and recrystallization from spinel- to plagioclase-facies conditions. Ongoing field and petrologic investigations have revealed that the peridotites experienced, during uplift, a composite history of diffuse melt migration and multiple episodes of ultramafic-mafic intrusions. In this paper we present the results of field, structural and petrologic-geochemical investigations into a sector of the Erro-Tobbio peridotite unit that preserves well this multiple intrusion history. Melt impregnation in the peridotites is evidenced by significant plagioclase enrichment and crystallization of unstrained orthopyroxene replacing kinked mantle olivine and clinopyroxene; impregnating melts were thus opx-saturated. Melt-rock interaction caused chemical changes in mantle minerals (e.g. Al decrease and REE increase in cpx; Ti and Cr# enrichment in spinel). Nevertheless, clinopyroxenes still exhibit LREE depletion (Ce;N;/Sm;N; = 0.006-0.011), indicating a depleted signature for the percolating melts. Melt impregnation was thus related to diffuse porous flow migration of depleted MORB-type melt fractions that modified their compositions towards opx saturation by mantle-melt interaction during ascent. The impregnated peridotites are intruded by a hectometer-scale stratified cumulate body, mostly consisting of troctolites and plagioclase wehrlites, showing gradational, interfingered contacts with the host mantle rocks. Subsequent intrusion events are revealed by the occurrence of olivine gabbros as decameter-wide lenses, variably thick (centimeter- to meter-scale) dykes and thin dykelets, which crosscut both the peridotite foliation and the magmatic layering in the cumulates. Overall, major and trace element compositions of minerals in the intrusives indicate that they represent variably differentiated cumulus products crystallized from rather primitive N-MORB-type aggregated melts. Slightly more evolved compositions are shown by olivine gabbros, relative to the troctolites and plagioclase wehrlites of the cumulate body. Mineral chemistry features (e.g. the Fo-An correlation and high Na, Ti, Mg# in cpx) indicate that the studied intrusive rocks crystallized at moderate pressure conditions (3-5 kbar, i.e. 9-15 km depth). Our study thus points to a progressive transition from porous flow melt migration to emplacement of magmas in fractures, presumably related to progressive change of lithospheric mantle rheology during extension-related uplift and cooling.
ISSN: 0024-4937

hal-00407669
https://hal.archives-ouvertes.fr/hal-00407669
DOI : 10.1016/j.lithos.2006.06.014

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Absolute earthquake hypocenter locations have been determined in the area offshore eastern Taiwan, at the Southernmost Ryukyu subduction zone. Location process is run within a 3D velocity model by combining the Taiwanese and neighboring Japanese networks and using the 3D MAXI technique. The study focuses on the most active seismic cluster in the Taiwan region that occurs in the forearc domain offshore eastern Taiwan. Earthquakes distribute mainly along 2 active planes. The first one aligns along the subduction interface and the second one, shallower affects the overriding margin. Focal mechanisms within the shallow group indicate that nodal planes are either compatible with high-angle back-thrusts or low-angle thrusts. The active seismic deformation exclusively indicates reverse faulting revealing that the forearc basement undergoes trench-perpendicular strong compression. By integrating the seismological image into the regional context, we favor the hypothesis in which the dense seismicity occurring offshore marks the activity of en-échelon high-angle reverse faults accommodating the uplift of a broken piece of Ryukyu Arc basement, called Hoping Basement Rise. The uplift is inferred to be caused by the subduction of an oceanic relief, either exotic block, seamount or oceanic crust sliver. Our favored solution satisfies the narrowness of epicenter's cluster along the Hoping Canyon, and the observation of high-angle active faults on seismic lines crossing the area. Furthermore, this solution is compatible with the active uplift of the Hoping Rise demonstrated from morphological and sedimentological data. We do not exclude the branching of the high-angle reverse faults system onto a splay fault connected with the subduction interface but further investigations are needed to map precisely the 3D distribution of active faults that break the margin.
ISSN: 0040-1951

hal-00407726
https://hal.archives-ouvertes.fr/hal-00407726
DOI : 10.1016/j.tecto.2007.11.018

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
After Jurassic rifting, numerous carbonate platforms (i.e., the Orizaba, Cordoba and Golden Lane-Tuxpan platforms) developed during the Lower and Middle Cretaceous episode of thermal subsidence along the western passive margin of the Gulf of Mexico, with intervening basinal domains (i.e., the Tampico-Misantla, Zongolica, Veracruz and Deep Gulf of Mexico - DGM - basins).;During the Late Cretaceous-Paleocene, the east-verging Sierra Madre Oriental thrust belt developed, resulting in tectonic uplift and unroofing of the allochthonous units (i.e. tectonic units made up of former Orizaba and Cordoba platforms and Zongolica Basin series). This new topography provided also an important source of clastics to feed the adjacent foredeep, where coeval tectonic loading accounted for the bending of the foreland lithosphere. However, shallow water facies or even emersion persisted until the Eocene in the forebulge area (at the present location of the Golden Lane), preventing locally the clastics to reach the DGM. This topographic barrier was ultimately bypassed by the clastics only during the Oligocene and Neogene, once (1) the prograding clastic wedge had exceeded accommodation, and (2) the long lasting thermal subsidence of the passive margin could overpass the effect of the bending and force the former bulge to sink.;Numerous paleo-thermo-meters (Tmax, Ro), paleo-thermo-barometers (fluid inclusions), PVT and coupled forward kinematic and thermal modeling have been used to calibrate and date the progressive unroofing of the thrust belt. Coupled tectonic and sedimentologic modeling was applied in the foreland to predict the distribution of sand versus shale ratios in the Oligocene to Plio-Quaternary clastic sedimentary wedge of the passive margin, where gravitational gliding of post-Eocene series occurred during the Neogene along major listric faults.;Mantle dynamics are advocated as the main process accounting for post-orogenic uplift and regional tilting of the basement, which initiated a massive transfer of sediments from the Cordillera towards the Gulf of Mexico, from Oligocene onward, resulting in a destabilization and gravitational collapse of the western slope of the Gulf of Mexico in Neogene times.
ISSN: 0040-1951

hal-00445248
https://hal.archives-ouvertes.fr/hal-00445248
DOI : 10.1016/j.tecto.2009.04.012

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We examine absolute gravity (AG) and vertical Global Positioning System (GPS) time series between 1995 and 2010 at eight collocated sites in mid-continent North America. The comparison of AG and GPS rates aligned to ITRF2005 yields a gravity/uplift ratio of -0.17 +/- 0.01 mu Gal mm(-1) (1 mu Gal = 10 nm s(-2)) and an intercept of -0.1 +/- 0.5 mm yr(-1). In contrast, aligning the GPS velocities to ITRF2000 results in a gravity/uplift intercept of -1.3 +/- 0.5 mm yr(-1). The near-zero gravity/uplift offset for the ITRF2005 (or ITRF2008) results shows a good alignment of the GPS vertical velocities to Earth's center of mass, and confirms that GPS velocities in this reference frame can be compared to predictions of geodynamic processes such as glacial isostatic adjustment (GIA) or sea-level rise. The observed gravity/uplift ratio is consistent with GIA model predictions. The ratio remains constant in regions of fast and slow uplift, indicating that GIA is the primary driving process and that additional processes such as local hydrology have a limited impact on a decadal time-scale. Combining AG and GPS measurements can provide significant constraints for geodetic, geodynamic, and hydrological studies. Citation: Mazzotti, S., A. Lambert, J. Henton, T. S. James, and N. Courtier (2011), Absolute gravity calibration of GPS velocities and glacial isostatic adjustment in mid-continent North America, Geophys. Res. Lett., 38, L24311, doi:10.1029/2011GL049846.
ISSN: 0094-8276

hal-00689010
https://hal.archives-ouvertes.fr/hal-00689010
DOI : 10.1029/2011GL049846

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Recent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46–48ºS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and/or tectonic events. We present new field observations from a region south of Lago General Carrera-Buenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5–4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (~2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause-and-effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction.
ISSN: 0954-4879

insu-00272075
https://hal-insu.archives-ouvertes.fr/insu-00272075
DOI : 10.1111/j.1365-3121.2007.00766.x

Éditeur(s) : HAL CCSD
Résumé : International audience
Continental erosion and weathering destroy parts of the stratigraphic record. Analyses of the sedimentary filling of paleokarsts help completing the geological record of regions that have been submitted to post-depositional, long-term, continental evolution. Jurassic carbonate platform of Languedoc (South of France) has undergone several karstification phases from Cretaceous to Neogene. Later incision of canyons through the carbonate massifs allows to observe paleokarsts over 400m depth, within the massifs. Paleokarsts are partly filled with sediments. Some have yielded marine bioclasts (echinoderms, radiolars), foraminifera and nannofossils; others are composed of polygenic detrital sediments, including sources from the upstream Paleozoic basement (Cevennes). The age of the filling of successive paleokarsts can be constrained by structural relationships and by biostratigraphy. These findings suggests 1) the marine elements of the karstic filling relate to a Late Cretaceous to Early Paleocene interval, while 2) the Paleozoic basement-sourced-sediments were trapped in the karst during Miocene to Present. Karstic sediment containing Early Paleocene foraminifera and nannofossils are found in paleokarsts cavities distributed across the entire thickness of the carbonate massif (≥350m). This requires base-level lowering and associated karstification, followed by base-level rise and karst filling of at least 350 m amplitude, respectively. The time interval corresponding to the occurrence of foraminifera and nannofossils in karsts covers 10 Myrs ; surprisingly, no equivalent marine sediments are preserved on the surface. In addition, analyses of the different forams species suggests several (up to 3) distinct karstification and marine filling cycles. Finally, sedimentological facies analysis of the karst filling reveals the following succession of processes: low energy settling of mudstone, high energy reworking, transport and deposition of silts and sandstones within the karst system. Integration of geological, paleontological and sedimentological data, leads to a polyphase scenario in response to repeated base-level variations, more than 350m amplitude. Such an amplitude excludes eustacy, and the improbable repeated sequence of uplift and subsidence rules out tectonics, as driving forces for base-level change, respectively. We propose that the high-amplitude base-level changes results from a succession of desiccation-flooding events of an endorheic, silled, basin during Early Paleogene. The later detrital assemblage sourced in the Cevennes occurs on perched paleosurfaces and in karst cavities across the whole 350m-deep canyon walls. When found on paleosurfaces, they correspond to the south-flowing Early Miocene fluvial drainage, and can be correlated downstream with the marine, well dated, Early Miocene, sediments. When found within the karst cavities, they correspond to successive base-level surfaces connected to the progressive incision of the canyon. This canyon incision is coeval with a Late Miocene uplift of the hinterland.
24th International Karstological School "Classical karst" : Paleokarst
Postojna, Slovenia

hal-01306683
https://hal-brgm.archives-ouvertes.fr/hal-01306683
https://hal-brgm.archives-ouvertes.fr/hal-01306683/document
https://hal-brgm.archives-ouvertes.fr/hal-01306683/file/Abstract_IKS.pdf

Éditeur(s) : Elsevier Science Bv
Résumé : In the South Gabon Basin, deep multi-channel seismic reflection and gravity modeling analysis have shed light on key features of the structure of the margin. The thinned continental crust beneath the Gabon Margin appears to be composed of two distinct layers, separated by a clear, strong and more or less continuous reflector running in the 7–10 s TWT window. The lower crust is characterized by a higher density, intermediate between the lower values of the upper crust and the denser values of the mantle. The lower crust is irregularly shaped and presents lateral thickness variations along the direction of thinning and along the coast. In the offshore thinned continental domain, the lower and upper crust form a 20–25 km thick body. Crustal thicknesses point to a relatively sharp and narrow transition, along a few tens of kilometers, between the unthinned and the thinned continental crust. The high density layer identified offshore Gabon presents similar characteristics in density, geometry and spatial distribution, as the underplated magmatic bodies observed along volcanic margins, e.g. along the South Atlantic Namibia Margin or the North Atlantic Vøring Margin. Although this lower crustal body could possibly represent ultra mafic serpentinized rocks or high grade metamorphic crustal rocks, we suggest that it could be composed of mafic rocks. Magmas resulting from partial melting during rifting may underplate the crust and/or be intruded in the lower crust through a system of dykes and sills. In this view, the present-day crustal thicknesses along rifted margins, characterized by magmatic underplating and/or intrusion, are not representative of the thinning that the crust experienced during rifting. Results of this study point to relatively shallow sedimentary basins along the South Gabon Margin. The deepest offshore depocenters located under the westernmost side of the continental platform appear to be associated with the deepest syn-rift basins These basins seem to extend along 20 to 40 km in the ~ NE–SW direction with a present-day average thickness of 7.3 km. Offshore Gabon, whereas the crustal thinning appears significant, the syn-rift deposit are not thick. We suggest that the area was anomalously uplifted during the rifting phase, due to an elevated thermal lithospheric gradient. The conclusions derived from our seismic and gravity analysis are consistent with the implications such a thermal anomaly would have on the tectonic evolution of a rifted margin with 1) an underplated high density lower crustal layer, 2) shallow depth syn-rift basins associated with a relatively thin crust and subsequently 3) elevated recorded subsidence rates in the initial post-rift stages. Research Highlights ► The Gabon Margin appears characterized by an underplated high density lower crustal layer. ► Shallow depth syn-rift basins are associated with a relatively thin crust. ► Seismic and gravity analysis points to an anomalous uplift of the Gabon Margin during the rifting phase. ► Crustal structure, syn-rift infill and post-rift subsidence are consistent an uplift of the Gabon Margin during the rifting phase. ► The uplift of the Gabon Margin is possibly due to an elevated thermal lithospheric gradient.
Tectonophysics (0040-1951) (Elsevier Science Bv), 2011-06 , Vol. 506 , N. 1-4 , P. 31-45

Droits : 2011 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00039/15020/12347.pdf
DOI:10.1016/j.tecto.2011.04.009
http://archimer.ifremer.fr/doc/00039/15020/

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Rainbow is a dome-shaped massif at the 36°14′N nontransform offset along the Mid-Atlantic Ridge. It hosts three ultramafic-hosted hydrothermal sites: Rainbow is active and high temperature; Clamstone and Ghost City are fossil and low temperature. The MoMARDREAM cruises (2007, 2008) presented here provided extensive rock sampling throughout the massif that constrains the geological setting of hydrothermal activity. The lithology is heterogeneous with abundant serpentinites surrounding gabbros, troctolites, chromitites, plagiogranites, and basalts. We propose that a W dipping detachment fault, now inactive, uplifted the massif and exhumed these deep-seated rocks. Present-day deformation is accommodated by SSW-NNE faults and fissures, consistent with oblique teleseismic focal mechanisms and stress rotation across the discontinuity. Faults localize fluid flow and control the location of fossil and active hydrothermal fields that appear to be ephemeral and lacking in spatiotemporal progression. Markers of high-temperature hydrothermal activity (∼350°C) are restricted to some samples from the active field while a more diffuse, lower temperature hydrothermal activity (<220°C) is inferred at various locations through anomalously high As, Sb, and Pb contents, attributed to element incorporation in serpentines or microscale-sulfide precipitation. Petrographic and geochemical analyses show that the dominant basement alteration is pervasive peridotite serpentinization at ∼160–260°C, attributed to fluids chemically similar to those venting at Rainbow, and controlled by concomitant alteration of mafic-ultramafic units at depth. Rainbow provides a model for fluid circulation, possibly applicable to hydrothermalism at oceanic detachments elsewhere, where both low-temperature serpentinization and magmatic-driven high-temperature outflow develop contemporaneously, channeled by faults in the footwall and not along the detachment fault.
ISSN: 1525-2027

hal-01115281
https://hal.archives-ouvertes.fr/hal-01115281
https://hal.archives-ouvertes.fr/hal-01115281/document
https://hal.archives-ouvertes.fr/hal-01115281/file/Andreani_et_al-2014-Geochemistry%2C_Geophysics%2C_Geosystems.pdf
DOI : 10.1002/2014GC005269

Éditeur(s) : HAL CCSD
Résumé : The evolution of mountain belt piedmont is controlled by interactions between tectonics, erosion and sedimentation. To study coupling between these processes, we analyze morphometric data collected in the eastern Tian Shan piedmont (NW China) and develop a new analogue modelling technique. The modeling approach uses an experimental set-up and analog material specifically designed to study simultaneously tectonic structures (faults, folds), detailed morphology (drainage basins, channels, alluvial fans, etc.) and stratified sedimentation. Measurement techniques based on laser interferometry and image correlation are also developed to quantify the topographic and kinematic evolution of models.
Our experiments allow a new approach for the study of piedmont morphotectonic evolution. Our results indicate that tectonics mainly controls this evolution. The propagation of deformation and the formation of relief both significantly influence the development of drainage networks, the evolution of drainage basins and the formation of morphotectonic markers. Particularly, a study of alluvial fans and watershed metrics suggests that there is a dynamical equilibrium between uplift, erosion and morphology. In addition, our results show that terrace nucleation is controlled by thrust activity and hydrography adjustments. Folding of terraces responds to a homothetic deformation pattern.
This new methodology brings promising perspectives in the fields of geomorphology, seismotectonics and sedimentology.
L'évolution d'un piémont de chaîne de montagnes est contrôlée par les interactions entre la tectonique, l'érosion et la sédimentation. Pour étudier ces processus, nous avons analysé des données morphométriques issues des piémonts orientaux du Tian Shan (NW Chine) et développé un nouveau type de modélisation analogique. Cette approche utilise un dispositif et un matériau expérimental spécialement conçus pour modéliser simultanément des structures tectoniques (failles, plis), une morphologie détaillée (bassins versants, rivières, cônes alluviaux, etc.) et une sédimentation stratifiée. Des techniques de mesure optique ont été également mises en oeuvre afin de quantifier l'évolution topographique et cinématique des modèles.
Les expériences réalisées offrent une opportunité inédite d'étudier l'évolution morphotectonique d'un piémont. Nos résultats montrent que la tectonique exerce un contrôle de premier ordre sur cette évolution. La propagation de la déformation et la formation des reliefs influencent en effet significativement le développement du réseau de drainage, l'évolution des bassins versants et la formation des marqueurs morphotectoniques. En particulier, l'analyse de la morphométrie des cônes alluviaux et de leurs bassins versants suggère qu'un équilibre dynamique s'installe entre la surrection, l'érosion et la morphologie. Nos résultats montrent également que l'apparition des terrasses est guidée par l'activité des chevauchements et les adaptations de l'hydrographie. Leur modèle de plissement répond à une déformation homothétique.
Cette nouvelle approche ouvre des perspectives d'étude prometteuses en géomorphologie, sismotectonique et stratigraphie.
https://tel.archives-ouvertes.fr/tel-00339145

tel-00339145
https://tel.archives-ouvertes.fr/tel-00339145
https://tel.archives-ouvertes.fr/tel-00339145v2/document
https://tel.archives-ouvertes.fr/tel-00339145/file/These_Graveleau08.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study provides an integrated review of plate tectonic models of the evolution of the Antarctica-Patagonia connection compared to geological records collected on land in Patagonia and Tierra del Fuego, and offshore along the northern edge of the Scotia Sea. A temporal framework for the sedimentary and tectonic events of the North Scotia Ridge and Tierra del Fuego is constructed with additional data compiled from entire Patagonia and the Austral Basin. This review provides robust correlations of seaways and tectonic events along the Scotia and South America plates and indicates that the opening of the Drake Passage was not steady state since ca. 30 Ma. Rather the regions forming the present-day northern limit of this gateway experienced important paleogeographic changes, from deep marine basins to shallow ridges and emerged regions during the late Oligocene and early-middle Miocene time. Our compilation of geological data shows that emergence along the North Scotia Ridge and Tierra del Fuego was achieved at 23-22 Ma, and has been followed by elimination of the Patagoniano Sea in Patagonia, starting at 22-23 Ma and achieved at 20 Ma. This transition towards more continental sedimentation in southern South America is correlated with more shallow marine conditions in the Austral Basin. This succession of events had a strong influence on the general geometry of the Drake Passage, corresponding to a constriction of its northern limit, starting in the window 29-22 Ma and achieved at 21 Ma. This period of active deformation in southern South America also corresponds to a period of the global climate having two anomalies well known from the isotopic records: the Late Oligocene Warming. around 26 Ma and the Mid-Miocene Climatic Optimum which ended between 15 and 14 Ma. The possible effects of the post-Oligocene tectonic evolution of the Drake Passage region on general oceanic circulation are discussed. Causes for the synchronicity between tectonic events and these global warming events are examined.
ISSN: 0012-821X

hal-00413525
https://hal.archives-ouvertes.fr/hal-00413525
DOI : 10.1016/j.epsl.2008.12.037

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present results of a geomorphological and morphotectonic analysis of the northeastern part of the Rif. We show that the present day kinematics of the Rif is characterized by active deformation along the Trougout and Nekor faults in the North-East. Digital Elevation Models of offset drainage features (streams, fluvial terraces) allow determining a normal-left-lateral motion along the Trougout fault and a left-lateral strike-slip motion along the Nekor fault. Preliminary 3He cosmogenic dates of tectonic markers yield vertical and horizontal slip rates of ∼0.9 mm/yr and ∼0.5 mm/yr, respectively along the Trougout fault. The present-day localized transtension seen in the north-eastern Rif morphology (Ras Tarf) is coeval with uplifted marine terraces near the Al Hoceima Bay. U/Th dating of shells yield an average uplift rate of ∼0.2 mm/yr during the past 500 ka. These data show that active transtension in the northeastern Rif is also associated with uplift. These new morphotectonic constraints are consistent with the GPS measurements showing southwestward overall motion of most of the Rif belt with respect to stable Africa.
ISSN: 0264-3707

hal-01053492
https://hal.archives-ouvertes.fr/hal-01053492
DOI : 10.1016/j.jog.2014.01.004

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Selected high-resolution seismic-reflection profiles and multibeam bathymetry acquired along the convergent Ecuador margin during the ATACAMES cruise on onboard the R/V L’Atalante (Jan.15–Feb.18, 2012) allow a preliminary evaluation of the neotectonic development and stratigraphic evolution of the margin based on the sismo-stratigraphic analysis of Quaternary sediment preserved on the margin shelf and upper slope. We present three major preliminary results. (1) The evolution of the Esmeraldas, Guayaquil and Santa Elena canyons. The head of the Esmeraldas canyon is the location of a continuous significant sediment transport. The Guayaquil canyon shows several episodes of deposition and incision. Aggrading sedimentation pattern in the canyon records several changes in relative sea-level. The subsidence of the Gulf of Guayaquil probably contributes to the good preservation of the canyon filling stages. The Santa Elena canyon is controlled by a SW–NE trending normal fault. (2) Variations of sediment accumulation and relative vertical motions are shown along-strike the shelf edge. Offshore the uplifted Manta peninsula, a pronounced subsidence of the shelf edge is documented by sedimentary clinoforms that have deposited in a morphological reentrant, and have migrated upslope testifying of a local subsidence meanwhile the adjacent La Plata Island area underwent uplift. In the Esmeraldas canyon area, a local uplift of the shelf is documented. (3) Two neotectonic fault systems with a possible transcurrent component are imaged across the shelf edge and upper margin slope offshore Jama, and Cape Galera. This possible transcurrent motion could be related to the reactivation of ancient faults of the upper plate by the subduction. These preliminary results indicate that the ATACAMES data set has a strong potential to evaluate the spatial and temporal contribution of tectonic and climate changes on the structural development and stratigraphic evolution of the Ecuador continental margin.
ISSN: 0025-3235

insu-01131151
https://hal-insu.archives-ouvertes.fr/insu-01131151
DOI : 10.1007/s11001-014-9231-y

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : Late Jurassic platform carbonates of Languedoc (southern France) are deeply incised by Late Miocene canyons, allowing the observation of karst systems filled with sediments containing evidences of marine origin. Field and structural relationships as well as new biostratigraphic data (planktonic foraminifera and calcareous nannofossils) provide a Latest Cretaceous-Earliest Paleocene age for the major karstification and a Paleocene (Danian-Selandian) age for the sedimentary filling. The ≥ 350 m vertical extent of this karst system and its subsequent marine filling gives a minimum amplitude for the base-level variation responsible for the karstification and then the marine flooding events. The observations suggest that at least, two marine successive events occurred in the Late Danian then in Selandian time. The large amplitude of base level is not in agreement with eustatic sea-level change, and the rate of base-level change is too fast for tectonic uplift and subsidence within the tabular, poorly deformed studied area. We propose a model of a silled endoreic basin, which was dessiccated and karstified over hundreds of meters, when it was disconnected from the World Ocean, and later suddently transgressed by the Paleocene sea and the karst flooded, when the bounding sill was submerged. Such a model is similar, although with significant differences, with the later Messinian-Zanclean event that affected the Mediterranean realm.
EISSN: 1777-5817

hal-00767556
https://hal.archives-ouvertes.fr/hal-00767556
DOI : 10.2113/gssgfbull.183.5.425