Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
New petrographic and microstructural observations, mineral equilibria modelling and U/Pb (monazite) geochronological studies were carried out to investigate the relationships between deformation and metamorphism across the Rehamna massif (Moroccan Variscan belt). In this area, typical Barrovian (muscovite to staurolite) zones developed in Cambrian to Carboniferous metasedimentary rocks that are distributed around a dome-like structure. First assemblages are characterized by the presence of locally preserved andalusite, followed by prograde evolution culminating at 6 kbar and 620 °C in the structurally deepest staurolite zone rocks. This Barrovian sequence was subsequently uplifted to supracrustal levels, heterogeneously reworked at greenschist facies conditions, which was followed locally by static growth of andalusite, indicating heating to 2.5–4 kbar and 530–570 °C. The 206Pb/238U monazite age of 298.3 ± 4.1 Ma is interpreted as minimum age of peak metamorphic conditions, whereas the ages of 275.8 ± 1.7 Ma and 277.0 ± 1.1 Ma date decompression and heating at low pressure, in agreement with previous dating of Permian granitoids intruding the Rehamna massif. The prograde metamorphism occurred during thickening and associated horizontal flow in the deeper crust (S1 horizontal schistosity). The horizontally disposed metamorphic zones were subsequently uplifted by a regional scale antiform during ongoing N–S compression. The re-heating of the massif follows late massive E–W shortening, refolding and retrograde shearing of all previous fabrics coevally with regionally important intrusions of Permian granitoids. We argue that metamorphic evolution of the Rehamna massif occurred several hundred kilometres from the convergent plate boundaries in the interior of continental Gondwanan plate. The tectonometamorphic history of the Rehamna massif is put into Palaeozoic plate tectonic perspective and Late Carboniferous reactivation of (Devonian)–Early Carboniferous basins formed during stretching of the north Gondwana margin and formation of the Palaeotethys Ocean. The inherited heat budget of these magma-rich basins plays a role in the preferential location of this intracontinental orogen. It is shown that rapid transition from lithospheric stretching to compression is characterized by specific HT type of Barrovian metamorphism, which markedly differs from similar Barrovian sequences along Palaeozoic plate boundaries reported from Variscan Europe.
ISSN: 0263-4929

hal-01468009
https://hal.archives-ouvertes.fr/hal-01468009
DOI : 10.1111/jmg.12214

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Karukéra spur is an easternmost submerged rise of the Lesser Antilles fore-arc in the Guadeloupe archipelago, culminating about 4000 m above the fore-arc basin 150 km west of the deformation front. The analysis of 3500 km 2D high-resolution multichannel seismic reflection and multibeam bathymetric data, and the study of 14 core samples, allow for the first time to reconstruct its sedimentary anatomy and tectonic evolution. Seven seismic units (US1 to US7) are evidenced, organised into four major depositional sequences separated by erosional surfaces. Units US1 to US4 thicken to the south-southeast on the spur. The sedimentary deposits rest upon a deeply eroded metamorphic basement of the Caribbean Plate as in La Désirade Island. Sequence 1 (units US1 and US2) remains unknown in its lower part because it does not outcrop. Its upper part comprises early Miocene shallow water carbonates. Sequence S2 (Unit US3) only comprises an upper Miocene transgressive systems tract deposited into basinal environment. It is bounded by major erosional surfaces SB2 and SB3. Sequence 3 (US4 to US6) is Zanclean to Pleistocene. It is dominantly composed of shallow water, reefal deposits. Sequence 4 corresponds to recent deposits. The Karukéra spur experienced three main extensional episodes with alternations between uplift and subsidence periods. Uplifts are responsible for emersions and erosions. Subsidence severely drowned shallow water deposits. The first extensional episode led to the formation of horsts and grabens in the basement, prior to early Miocene deposits. The second extensional episode occurred during upper Miocene, in accordance with data in surrounding islands. The third tectonic episode developed since Calabrian. Noticeable is the constant reactivation of N130°–N150°, N150°–N180° and N40° trending faults since early Miocene and the neoformation of E–W trending faults since Calabrian. Our results suggest that at the latitude of Guadeloupean archipelago the Lesser Antilles subduction zone is an erosional margin because of the successive sweepings of the Santa Lucia then Tiburon Ridges.
ISSN: 0025-3227

hal-01172231
https://hal.archives-ouvertes.fr/hal-01172231
DOI : 10.1016/j.margeo.2015.02.007

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : International audience
– The 300 km long allochthonous sheet of oceanic mantle forming the New Caledonia ophiolite displays three specific characters: 1) the ophiolite pile lacks concordant sheeted dykes and pillow basalt layers; 2) the ophiolite, refered to as the Peridotite nappe, is thrusted over the basaltic formations of the Poya terrane which are classicaly thought to originate from a different oceanic environment; 3) The basal contact of the ultramafic sheet is remarkably flat all along New-Caledonia and the Peridotite nappe has not been thickened during obduction, rather it experienced significant extension. This suggests that the peridotites have not been emplaced by a tectonic force applied to the rear. New petrological and geochemical results obtained from mantle rocks finally show that the Poya terrane may originate from the same oceanic basin as the peridotites. In this article, we consider such possible cogenetic links and we propose a simple model for the obduction of the New Caledonia ophiolite in which the Poya basalts represent the original cover of the Peridotite nappe. We infer that continuous uplift of the subducted units buried beneath the oceanic lithosphere in the northern part of New Caledonia drove passive uplift of the ophiolite and led to erosion and to initiation of sliding of the basaltic layer. During the Priabonian (latest Eocene), products of the erosion of the basaltic layer were deposited together with sediments derived from the Norfolk passive oceanic margin. These sediments are involved as tectonic slices into an accretionary wedge formed in response to plate convergence. The volcaniclastic sedimentation ends up with the emplacement of large slided blocks of basalts and rafted mafic units that progressively filled up the basin. Obduction process ended with the gravity sliding of the oceanic mantle sheet, previously scalped from its mafic cover. This process is contemporaneous with the exhumation of the HP-LT units of Pouebo and Diahot. Gravity sliding was facilitated by the occurrence of a continuous serpentine sole resulting from metasomatic hydratation of mantle rocks, which developed during the uplift of the Norfolk basement and overlying Diahot and Pouébo units. Progressive emersion of the obducted lithosphere allowed subsequent weathering under subaerial, tropical conditions. Obduction passive et mise en place gravitaire des grandes nappes ophiolitiques : les ophiolites de Nouvelle-Calédonie (SW Pacifique) sont-elles un cas d'école ? Résumé. – La nappe de manteau de Nouvelle-Calédonie, s'étendant sur 300 km de long montre trois caractéristiques im-portantes: 1) La succession ophiolitique ne contient ni dykes, ni basaltes en coussin, 2) l'ophiolite est charriée sur des formations basaltiques (nappe de Poya) que l'on considère classiquement comme originaires d'un bassin océanique dif-férent de celui d'où est issu le manteau, et 3) le contact basal de la nappe ultrabasique est remarquablement plat tout le long de l'île et celle-ci n'a pas été épaissie durant l'obduction. Cela suggère que les péridotites n'ont pas été mises en place en réponse à une poussée tectonique arrière. De nouveaux résultats pétrologiques et géochimiques obtenus sur l'ophiolite montrent en réalité que les basaltes de Poya peuvent être extraits de la fusion du manteau de l'ophiolite. Nous proposons donc un nouveau modèle pour l'obduction, dans lequel les basaltes de Poya forment la couver-ture initiale primitive du manteau de la nappe des péridotites. La surrection progressive des unités profondes enfouies lors de la subduction de la lithosphère du bassin sud-Loyauté à l'Eocène, a permis le soulèvement passif de l'ophiolite et l'érosion puis le glissement des unités basaltiques. Durant le Priabonien, l'accumulation des produits de l'érosion de la couche des basaltes et de la marge passive de Norfolk ont formé les séquences de flysch comprenant localement des débris basaltiques grossiers. Ces sédiments font partie d'un prisme d'accrétion tectonique construit en réponse à la convergence au front de la subduction. La sédimentation détritique se termine par la mise en place de grandes unités ba-saltiques glissées qui comblent le bassin. Le processus de l'obduction se termine par le glissement gravitaire de l'écaille de manteau océanique sur les basaltes. Cet événement est contemporain de l'exhumation des unités HP-BT de Pouébo et du Diahot. Le glissement gravitaire a été facilité par la présence sous l'ophiolite, d'une semelle continue de serpentines résultant de l'interaction du manteau avec des fluides métasomatiques remontant durant l'exhumation des unités en-fouies pendant la subduction continentale. L'émersion progressive de la lithosphère obduite a placé le manteau dans des conditions d'altération supergène tropicale.
EISSN: 1777-5817

hal-01257702
https://hal.archives-ouvertes.fr/hal-01257702
https://hal.archives-ouvertes.fr/hal-01257702/document
https://hal.archives-ouvertes.fr/hal-01257702/file/Lagabrielleetal-BSGF-2012-revised-light.pdf
DOI : 10.2113/gssgfbull.184.6.545

Éditeur(s) : AGU
Résumé : New, high-quality multichannel seismic reflection data from the western New Caledonia offshore domain allow for the first time the direct, continuous connection of seismic reflectors between the Deep Sea Drilling Project 208 drill hole on the Lord Howe Rise and the New Caledonia Basin. A novel seismic interpretation is hence proposed for the northern New Caledonia Basin stratigraphy, which places the Eocene/Oligocene unconformity deeper than previously thought and revisits the actual thickness of the pre-Oligocene sequences. A causal link is proposed between the obduction of the South Loyalty Basin over New Caledonia (NC) and the tectonic history of the northern New Caledonia Basin. Here it is suggested that as the South Loyalty Basin was being obducted during early Oligocene times, the NC Basin subsided under the effect of the overloading and underthrusted to accommodate the compressional deformation, which resulted in (1) the uplift of the northern Fairway Ridge and (2) the sinking of the western flank of New Caledonia. This event also had repercussions farther west with the incipient subsidence of the Lord Howe Rise.
Tectonics (0278-7407) (AGU), 2008-12 , Vol. 27 , N. TC6006 , P. 1-20

Droits : 2008 American Geophysical Union
http://archimer.ifremer.fr/doc/2008/publication-4782.pdf
DOI:10.1029/2008TC002263
http://archimer.ifremer.fr/doc/00000/4782/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In order to better constrain the relationship between tectonics and sedimentation of the Eastern Sardinian Margin, from the Messinian to the present day (METYSS project), a lithostratigraphic study was carried out on the Late Neogene deposits along the Cedrino Valley (eastern Sardinia). The late Neogene evolution is documented from sedimentological and tectonic analysis, biostratigraphic dating, and by mapping and logging stratigraphic sections. Previous authors have differentiated an early Pliocene marine formation from an older continental formation, possibly Miocene, the entire system being covered by late Pliocene to Quaternary lava flows. Preliminary biostratigraphic data suggest the absence of the lowermost Pliocene, based on the absence of Globorotalia margaritae and the presence of Globorotalia puncticulata, implying a sediment age between 3.81 and 2.41 Ma. At the foot of the Fiuli cliff, some mud clasts include a coccolith microflora, Tortonian in age, suggesting reworking. The Pliocene marine deposits consist of a single filling sequence instead of a succession of superimposed sequences as we would expect during this period of time; the occurrences of terms rarely respect the usual transgressive-regressive succession. Contrasting bathymetric environments (fore-shore, pro-delta, shelf or upper slope) can be abruptly superimposed on top of the other, along few meter thick intervals. A rapidly flooded term is observed in several sites and indicates a spatial variability over only a few kilometers distance. Some deep water deposits are in the middle of the infilling Pliocene sequence, whereas shallower water deposits can be repeated along a vertical section, or even interrupted by emersion. These marked differences can express syn-, or possibly post-sedimentation tectonic uplifts. The 10–25° bed dips originated through local tectonic uplift. At Fiuli, the geometry of the bedding planes is indicative of tilting toward the west, in a direction opposite to the one observed at Onifai. These Pliocene series form a wide syncline with an approximately NNE–SSW axis. This morpho-structural behavior appears to be largely atypical of this East-Sardinian coastal area.
ISSN: 1040-6182

hal-01134707
https://hal.archives-ouvertes.fr/hal-01134707
DOI : 10.1016/j.quaint.2014.11.022

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Tectonically controlled landforms develop morphologic features that provide useful markers to investigate crustal deformation and relief growth dynamics. In this paper, we present results of morphotectonic experiments obtained with an innovative approach combining tectonic and surface processes (erosion, transport, and sedimentation), coupled with accurate model monitoring techniques. This approach allows for a qualitative and quantitative analysis of landscape evolution in response to active deformation in the three end-member geological settings: compression, extension, and strike–slip.Experimental results outline first that experimental morphologies evolve significantly at a short time scale. Numerous morphologic markers form continuously, but their lifetime is generally short because erosion and sedimentation processes tend to destroy or bury them. For the compressional setting, the formation of terraces above an active thrust appears mainly controlled by narrowing and incision of the main channel through the uplifting hanging-wall and by avulsion of deposits on fan-like bodies. Terrace formation is irregular even under steady tectonic rates and erosional conditions. Terrace deformation analysis allows retrieving the growth history of the structure and the fault slip rate evolution. For the extensional setting, the dynamics of hanging-wall sedimentary filling appears to control the position of the base level, which in turn controls footwall erosion. Two phases of relief evolution can be evidenced: the first is a phase of relief growth, and the second is a phase of upstream propagation of topographic equilibrium that is reached first in the sedimentary basin. During the phase of relief growth, the formation of triangular facets occurs by degradation of the fault scarp, and their geometry (height) becomes stationary during the phase of upstream propagation of the topographic equilibrium. For the strike–slip setting, the complex morphology of the wrench zone, composed of several interacting fault segments, enhances the interactions with the drainage network. Because of the widening of the main fault zone toward the surface, a significant amount of distributed deformation is observed along the wrench zone. Locally, where two terminations of fault segments interact, less than a quarter of the far field displacement can remain measurable using fault offsets, leading to a systematic underestimation of the real fault slip rate.These different experimental examples illustrate the great potential of the approach coupling deformation mechanisms and erosion–transport–sedimentation processes to investigate qualitatively and quantitatively the morphotectonic evolution of tectonically controlled landscapes.
ISSN: 0169-555X

hal-01243587
https://hal.archives-ouvertes.fr/hal-01243587
DOI : 10.1016/j.geomorph.2015.02.011

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
A dense, local network of 30 geodetic markers covering a 50 × 60 km2 area in the southwestern European Alps (Briançon region) has been temporarily surveyed in 1996, 2006 and 2011 by GPS. The aim is to measure the current deformation in this seismically active area. The study zone is characterized by a majority of extensional and dextral focal mechanisms, along north–south to N160 oriented faults. The combined analysis of the three measurement campaigns over 15 years and up to 16 years of permanent GPS data from the French RENAG network now enables to assess horizontal velocities below 1 mm/year within the local network. The long observation interval and the redundancy of the dense campaign network measurement help to constrain a significant local deformation pattern in the Briançon region, yielding an average E–W extension of 16 ± 11 nanostrain/year. We compare the geodetic deformation field to the seismic deformation rate cumulated over 37 years, and obtain good coherencies both in amplitude and direction. Moreover, the horizontal deformation localized in the Briançon region represents a major part of the Adriatic-European relative plate motion. However, the average uplift of the network in an extensional setting needs the presence of buoyancy forces in addition to plate tectonics.
ISSN: 0264-3707

hal-01119724
https://hal.archives-ouvertes.fr/hal-01119724
DOI : 10.1016/j.jog.2015.02.001

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Two-dimensional simulations using a thermomechanical model based on a finite-difference method on a staggered grid and a marker in cell method are performed to study the plume-lithosphere interaction beneath moving plates. The plate and the convective mantle are modelled as a homogeneous peridotite with a Newtonian temperature- and pressure-dependent viscosity. A constant velocity, ranging from 5 to 12.5 cm yr−1, is imposed at the top of the plate. Plumes are generated by imposing a thermal anomaly of 150 to 350 K on a 50 km wide domain at the base of the model (700 km depth); the plate atop this thermal anomaly is 40 Myr old. We analyse (1) the kinematics of the plume as it impacts the moving plate, (2) the dynamics of time-dependent small-scale convection (SSC) instabilities developing in the low-viscosity layer formed by spreading of hot plume material at the base of the lithosphere and (3) the resulting thermal rejuvenation of the lithosphere. The spreading of the plume material at the base of the lithosphere, characterized by the ratio between the maximum down- and upstream horizontal (dimensionless) velocities in the plume-fed sublithospheric layer, Peup/Pedown depends on the ratio between the maximum plume upwelling velocity and the plate velocity, Peplume/Peplate. For fast plate velocities and sluggish plumes (low Peplume/Peplate), plate motion drags most plume material and downstream flow is dominant. As Peplume/Peplate increases, an increasing part of the plume material flows upstream. SSC systematically develops in the plume-fed sublithospheric layer, downstream from the plume. Onset time of SSC decreases with the Rayleigh number. For vigorous plumes, it does not depend on plate velocity. For more sluggish plumes, however, variations in the plume spreading behaviour at the base of the lithosphere result in a decrease in the onset time of SSCs with increasing plate velocity. In any case, SSC results in uplift of the isotherm 1573 K by up to 20 km relative to its initial equilibrium depth at the impact point.
ISSN: 0956-540X

hal-00856763
https://hal.archives-ouvertes.fr/hal-00856763
DOI : 10.1093/gji/ggt128

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The investigation of deformation rates on a mountain piedmont can provide key information for improving our understanding of the overall dynamics of a mountain range. Here, we estimate the shortening rate absorbed by a Quaternary emergent detachment fold on the southeastern piedmont of the Tianshan (China). Our work is primarily based on new 10Be cosmogenic exposure dating of deformed alluvial surfaces. The method we have developed combines depth profiling with sampling of surface cobbles, thereby allowing exposure time, erosion rate and inheritance to be simultaneously constrained. The exposure ages of the uppermost uplifted alluvial surfaces are around 140±17 ka140±17 ka, 130±9 ka130±9 ka and 47±9 ka47±9 ka, from west to east. A terrace lying below the 140 ka surface is dated at 65±5 ka65±5 ka. The ages of the uplifted and folded alluvial surfaces were then combined with estimates of shortening obtained using two distinct methods: (1) the excess area method, where sedimentation rates, extracted from magnetostratigraphic studies, are used to determine the amount of sedimentation after the abandonment of the river; and (2) a folding model derived from sandbox experiments. The late Pleistocene shortening rates are shown to be between 0.4±0.1 mm/yr0.4±0.1 mm/yr and 0.8±0.5 mm/yr0.8±0.5 mm/yr on the western part of the fold and 2.1±0.4 mm/yr2.1±0.4 mm/yr along its central part. The central part of the frontal Yakeng anticline therefore accommodates up to 25% of the total shortening currently absorbed across the whole Eastern Tianshan range (8 mm/yr). However, this situation seems to have prevailed for only the last 150 ka, as the shortening rate absorbed by this nascent fold was previously ten times slower. While the initiation of folding of the Yakeng anticline can be traced back to 5.5 Ma ago, the basinward migration of the active deformation front onto the Yakeng fold is a relatively recent phenomenon and appears to be diachronous from west to east, probably in relation to the tectonic activity of the folds in the hinterland.
ISSN: 0012-821X

hal-01306997
https://hal.archives-ouvertes.fr/hal-01306997
DOI : 10.1016/j.epsl.2015.11.041

Éditeur(s) : HAL CCSD
Résumé : 38 pages
Rapport
The Chicxulub impact crater, México, is unique. It is the only known terrestrial impact structure that has been directly linked to a mass extinction event and the only terrestrial impact with a global ejecta layer. Of the three largest impact structures on Earth, Chicxulub is the best preserved. Chicxulub is also the only known terrestrial impact structure with an intact, unequivocal topographic peak ring. Chicxulub’s role in the Cretaceous/Paleogene (K-Pg) mass extinction and its exceptional state of preservation make it an important natural laboratory for the study of both large impact crater formation on Earth and other planets and the effects of large impacts on the Earth’s environment and ecology. Our understanding of the impact process is far from complete, and despite more than 30 years of intense debate, we are still striving to answer the question as to why this impact was so catastrophic.During International Ocean Discovery Program (IODP) Expedition 364, Paleogene sediments and lithologies that make up the Chicxulub peak ring were cored to investigate (1) the nature and formational mechanism of peak rings, (2) how rocks are weakened during large impacts, (3) the nature and extent of post-impact hydrothermal circulation, (4) the deep biosphere and habitability of the peak ring, and (5) the recovery of life in a sterile zone. Other key targets included sampling the transition through a rare midlatitude section that might include Eocene and Paleocene hyperthermals and/or the Paleocene/Eocene Thermal Maximum (PETM); the composition and character of the impact breccias, melt rocks, and peak-ring rocks; the sedimentology and stratigraphy of the Paleocene–Eocene Chicxulub impact basin infill; the chronology of the peak-ring rocks; and any observations from the core that may help us constrain the volume of dust and climatically active gases released into the stratosphere by this impact. Petrophysical property measurements on the core and wireline logs acquired during Expedition 364 will be used to calibrate geophysical models, including seismic reflection and potential field data, and the integration of all the data will calibrate impact crater models for crater formation and environmental effects. The proposed drilling directly contributes to IODP Science Plan goals:Climate and Ocean Change: How resilient is the ocean to chemical perturbations? The Chicxulub impact represents an external forcing event that caused a 75% level mass extinction. The impact basin may also record key hyperthermals within the Paleogene.Biosphere Frontiers: What are the origin, composition, and global significance of subseafloor communities? What are the limits of life in the subseafloor? How sensitive are ecosystems and biodiversity to environmental change? Impact craters can create habitats for subsurface life, and Chicxulub may provide information on potential habitats for life, including extremophiles, on the early Earth and other planetary bodies. Paleontological and geochemical studies at ground zero will document how large impacts affect ecosystems and effects on biodiversity.Earth Connections/Earth in Motion: What are the composition, structure and dynamics of Earth’s upper mantle? What mechanisms control the occurrence of destructive earthquakes, landslides, and tsunami? Mantle uplift in response to impacts provides insight into dynamics that differ between Earth and other rocky planets. Impacts generate earthquakes, landslides, and tsunami, and scales that generally exceed plate tectonic processes yield insight into effects, the geologic record, and potential hazards.IODP Expedition 364 was a Mission Specific Platform expedition to obtain subseabed samples and downhole logging measurements from the sedimentary cover sequence and peak ring of the Chicxulub impact crater. A single borehole was drilled into the Chicxulub impact crater on the Yucatán continental shelf, recovering core from 505.7 to 1334.73 m below seafloor with ~99% core recovery and acquiring downhole logs for the entire depth.
International Ocean Discovery Program

hal-01639520
https://hal.archives-ouvertes.fr/hal-01639520
DOI : 10.14379/iodp.pr.364.2017

Éditeur(s) : D. Reidel Publishing Company, Dordrecht- Holland
Résumé : Serial seismic reflection profiles off Tunisia and between Sardinia and Tunisia are presented. Interpretation is given which includes paleozoïc basement and its autochtonous (Eocene and plio-quaternary) and allochtonous (Numidian nappe) cover. Recent tectonic activity is discussed, (Plio-quaternary foundered basins, 'flexure', local uplifts, intrusions). Then the nature of the basement of the Sardinia-Tunisia zone is discussed with respect to the various hypotheses on the region of the Western Mediterranean. [NOT CONTROLLED OCR]
Une série de profils de sismique réflexion effectués au large de la Tunisie et dans le détroit sardano-tunisien aboutissent à l'élaboration d'un schéma géologique interprétatif dans lequel nous replaçons le socle paléozoïque et sa couverture autochtone (Eocène et plio-quaternaire) et allochtone (nappe numidienne). Nous discutons ensuite des manifestations néotectoniques (bassins d'effondrements plio-quaternaires - mouvement de flexure - surrections locales - venues intrusives). Enfin la nature du substratum du détroit sardano-tunisien est discutée en liaison avec les hypothèses dynamiques et statiques relatives à la formation de la Méditerranée occidentale. [OCR NON CONTRÔLE]
Marine Geophysical Researches (D. Reidel Publishing Company, Dordrecht- Holland), 1970-06 , Vol. 1 , P. 162-177

Droits : D. Reidel Publishing Company, Dordrecht- Holland
http://archimer.ifremer.fr/doc/1970/publication-4912.pdf
http://archimer.ifremer.fr/doc/00000/4912/

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : International audience
The interplay between tectonics and erosion has a predominant control on the evolution of the morphology of mountain belts. Here we investigate the modalities of deformation in Central Nepal on a c. 100 ka time scale in response to tectonic and external forcings, through the use of a finite-element thermomechanical model coupled with an integrative denudation formulation that accounts for fluvial incision and hillslope landsliding. We study the complex coupling existing between tectonics and erosion, with special emphasis on the influences of rock strength and rainfall distributions. Our results underline the key role played by lithologic variations in the elevation of both rivers and mean topography. We show that the location of the Main Frontal Thrust is mainly controlled by the low erodability of the unconsolidated sandstone in the Siwaliks Hills. As previously suspected (Burbank et al. 2003), our simulations demonstrate that the pattern of uplift in Nepal is mainly dependent on both erodability and fault geometry, rather than on rainfall distribution.
ISSN: 2041-4927

hal-01543331
https://hal-amu.archives-ouvertes.fr/hal-01543331
DOI : 10.1144/GSL.SP.2006.253.01.18

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
A network of 54 survey GPS sites, 28 continuous GPS stations and three absolute gravity (AG) observation sites have been set up in the Alborz mountain range to quantify the present-day kinematics of the range. Our results allow us to accurately estimate the motion of the South Caspian block (SCB) for the first time, and indicate rotation of the SCB relative to Eurasia, accounting for the left lateral motion in the Alborz range. In light of these new results, it clearly appears that deformation rates vary along the range, the eastern part accommodating mainly left lateral strike slip (2 mm yr(-1) south of the range and 5 mm yr(-1) north of the range) with a very low range normal shortening rate on the Khazar thrust fault (similar to 2 mm yr(-1)), and the western part accommodating range normal shortening (similar to 6 mm yr-1) on the Khazar thrust fault with a left lateral component of similar to 2 mm yr(-1) north of the range and 1 mm yr(-1) south of the range. These present-day kinematics agree with geomorphologic estimated slip rates, but not the long-term deformation, corroborating the idea that the kinematics of the range have changed recently due to the change of SCB motion.;Modelling of the interseismic deformation suggests a deep locking depth on the central-western segment of the Khazar fault (similar to 30 km) in agreement with the Baladeh earthquake rupture and aftershock ranging between 10 and 30 km. Given this unusual deep locking depth and the 34 degrees dip of the thrust, a large part of the Alborz range is located above the seismically coupled part of the fault. Based on our AG measurements this part of the range seems to uplift at a rate of 1-5 mm yr(-1), in agreement with terrace uplift.
ISSN: 0956-540X

hal-00617146
https://hal.archives-ouvertes.fr/hal-00617146
https://hal.archives-ouvertes.fr/hal-00617146v2/document
https://hal.archives-ouvertes.fr/hal-00617146/file/djamour2010.pdf
DOI : 10.1111/j.1365-246X.2010.04811.x

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Seismic reflection profiles from the sediment rich Alaska subduction zone image short, frontally accreted, imbricate thrust slices and repeated sequences of long, underthrust sheets. Rapid landward increases in wedge thickness, backthrusting, and uplift of the forearc are observed, suggesting underthrusting beneath the wedge. These features and a widely varying frontal wedge morphology are interpreted to be caused by different modes of accretion active concurrently along the trench at different locations. Episodic wedge growth is observed in high basal friction experiments using sand as an analog material. Two phases of an accretionary cycle can be distinguished: frontal accretion of short imbricate thrust slices, alternating with underthrusting of long, undeformed sheets. The phase is shown experimentally to depend upon the surface slope of the wedge. Mechanical analysis of the forces at work predicts these two modes of deformation due to the varying frictional forces and yield strengths for a temporally varying wedge geometry. Maximum length of thrust slices is calculated for experimental conditions and confirmed by the observations. For a steep frontal slope (at the upper limit of the Mohr-Coulomb taper stability field) the overburden is too great to permit underthrusting, and failure occurs repeatedly at the wedge front producing short imbricate slices. The wedge grows forward, lowering the surface angle to the minimum critical taper. For a shallow frontal slope the reduced overburden along an active roof thrust permits sustained underthrusting, causing frontal erosion and backthrusting, steepening the wedge and thus completing the cycle.
ISSN: 0148-0227

hal-01261538
https://hal.archives-ouvertes.fr/hal-01261538
https://hal.archives-ouvertes.fr/hal-01261538/document
https://hal.archives-ouvertes.fr/hal-01261538/file/gutscherJGR1998.pdf

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
Detailed seafloor mapping in the area east of Taiwan revealed trench-parallel stretching and folding of the Ryukyu forearc and lateral motion of the accretionary wedge under oblique convergence. East of 122ø40'E, a steep accretionary wedge is elongated in an E-W direction. A major transcurrent right-lateral strike-slip fault accommodates the strain partitioning caused by an oblique convergence of 40 ø. A spectacular out-of-sequence thrust may be related to the subduction of a structural high lying in the axis of the N-S trending Gagua Ridge. This asperity is likely responsible for the uplift of the accretionary wedge and forearc basement and may have augmented strain partitioning by increasing the coupling between the two plates. West of 122ø40'E, the low-taper accretionary wedge is sheared in a direction subparallel to the convergence vector with respect to the Ryukyu Arc. The bayonet shape of the southern Ryukyu Arc slope partly results from the recent (re)opening of the southern Okinawa Trough at a rate of about 2 to 4 cm/yr. Right-lateral shearing of the sedimentary forearc with respect to the nonlinear Ryukyu backstop generates trench-parallel extension in the forearc sediment sequence at dilational jogs and trench-parallel folding at compressive jogs. The Hoping Basin lies above a diffuse trench/trench/fault (TTF) or TFF unstable triple junction moving toward the south along a N-S transform zone which accommodates the southward drift of the Ryukyu Arc with respect to Eurasia.
ISSN: 0278-7407

hal-01261555
https://hal.archives-ouvertes.fr/hal-01261555
https://hal.archives-ouvertes.fr/hal-01261555/document
https://hal.archives-ouvertes.fr/hal-01261555/file/Lallemand_et_al-1999-Tectonics.pdf
DOI : 10.1029/1998TC900011

Éditeur(s) : HAL CCSD
Résumé : Poster
The Lesser Caucasus in Armenia is an active volcanic and tectonic zone which resulted from the collision of the Arabian and the Eurasian plates since Neogene times. The During Quaternary, Lesser Caucasus was uplifted (0.3 mm/yr; Mitchell and Westaway, 1999) and experienced extensional tectonics times. Large lakes developed in graben structures. The diatomitic sequences of the Shamb paleo-lake (South Armenia) offer a rare opportunity to give new insights of Western Asia paleo-climate. Based on macroflora analysis, Bruch and Gabrielyan (2002) proposed a cooling and drying general climate trend through Pleistocene times in relation with a general uplift of the chain. Several questions have to be answer for this poorly investigated region. Did the climate record humid glacials and arid interglacials as suggested northward in Kazakhstan? What are the vegetation and climate responses to orbital parameters and to the monsoon? Moreover the lesser Caucasus is known as the entrance way used by the first hominids in Eurasia during Pleistocene time. How was the environment at this time? We present an integrated palynological, 40Ar/39Ar isotopic and magnetostratigraphic study for the most complete section (Joannin et al., in press). 40Ar/39Ar dating of two volcaniclastic layers provided ages of 1.24 ± 0.03 and 1.16 ± 0.02 Ma (2. Magnetostratigraphic data show that the entire Shamb section is of reversed polarity which correlates with part of the Matuyama period (1.785-1.070 Ma). Pollen assemblages and macroremains diversity revealed an alternation of glacial and interglacial phases that are compared with climate changes inferred from the global isotopic curve. The Shamb section ranges from approximately 1.300 to 1.080 Ma in age (marine isotopic stages 40 to 31). The vegetation of the Lesser Caucasus developed in a mosaic pattern in a Pleistocene continental, mostly arid climate, similar to the present-day climate. The vegetation changes record a dominant climate response to the obliquity orbital parameter. The influence of precession could not be established from the Shamb data. Pollen and macroflora both indicate that glacial periods were cold and dry and that interglacials were warm with local humidity. The early Pleistocene climatic model for Western Asia is thus similar to the climatic model for the Mediterranean area. Bruch, A., Gabrielyan, I.G., 2002. Quantitative data of the Neogene climatic development in Armenia and Nakhichevan. Acta Universitatis Carolinae – Geologica 46, 41–48. Joannin, S., Cornée, J.J., Münch, P., Fornari, M., Vasiliev, J., Krijgsman, W., Nahapetyan, S., Gabrielyan, Y., Ollivier, V., Roiron, P., Chataîgnier, C. In press. Early Pleistocene climatic cycles in continental deposits of the Lesser Caucasus of Armenia inferred from palynology, magnetostratigraphy, and 40Ar/39Ar dating. Earth and Planetary Science Letters. Mitchell, J., Westaway, R., 1999. Chronology of Neogene and Quaternary uplift and magmatism in the Caucasus: constraints from K-Ar dating of volcanism in Armenia. Tectonophysics 304, 157–186.
EGU Eurasian Climate and Tectonics
Vienne, Austria

hal-00481799
https://hal.archives-ouvertes.fr/hal-00481799

Éditeur(s) : HAL CCSD American Geophysical Union (AGU) American Geophysical Union
Résumé : International audience
GPS data reveal that the Brahmaputra Valley has broken from the Indian Plate and rotates clockwise relative to India about a point a few hundred kilometers west of the Shillong Plateau. The GPS velocity vectors define two distinct blocks separated by the Kopili fault upon which 2–3 mm/yr of dextral slip is observed: the Shillong block between longitudes 89 and 93°E rotating clockwise at 1.15°/Myr and the Assam block from 93.5°E to 97°E rotating at ≈1.13°/Myr. These two blocks are more than 120 km wide in a north-south sense, but they extend locally a similar distance beneath the Himalaya and Tibet. A result of these rotations is that convergence across the Himalaya east of Sikkim decreases in velocity eastward from 18 to ≈12 mm/yr and convergence between the Shillong Plateau and Bangladesh across the Dauki fault increases from 3 mm/yr in the west to >8 mm/yr in the east. This fast convergence rate is inconsistent with inferred geological uplift rates on the plateau (if a 45°N dip is assumed for the Dauki fault) unless clockwise rotation of the Shillong block has increased substantially in the past 4–8 Myr. Such acceleration is consistent with the reported recent slowing in the convergence rate across the Bhutan Himalaya. The current slip potential near Bhutan, based on present-day convergence rates and assuming no great earthquake since 1713 A.D., is now ~5.4 m, similar to the slip reported from alluvial terraces that offsets across the Main Himalayan Thrust and sufficient to sustain a Mw ≥ 8.0 earthquake in this area.
ISSN: 0148-0227

hal-01115084
https://hal.archives-ouvertes.fr/hal-01115084
DOI : 10.1002/2014JB011196

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The island of Taiwan is located on the convergent boundary between the Philippine Sea plate and the Chinese continental margin. It offers very active mountain building and collapsing processes well illustrated by the rugged topography, rapid uplift and denudation, young tectonic landforms, active faulting and numerous earthquakes. In this paper, using simple models, we have estimated vertical movements and associated absolute gravity variations which can be expected along a profile crossing the southern part of the island and probably suffering the highest rates of rising. The two different tectonic styles proposed for the island, thin-skinned and thick-skinned, were taken into account. Horizontal and vertical movements were modeled by an elastic deformation code. Gravity variations due to these deformations are then modeled at a second step. They are dominated by plate and free-air effects, i.e. elevation of the topography, with several mu Gal yr(-1). By comparison, gravity changes generated by mass transfers are weak: maximum 0.1 mu Gal yr(-1) with the thin-skinned tectonic and 0.3 mu Gal yr(-1) with the thick-skinned tectonic. Though elastic rheology has limitations, this modeling offers interesting results on what gravity signal can be expected from the AGTO project (Absolute Gravity in the Taiwanese Orogen), which proposes to study the dynamic of these mountain ranges using absolute gravimetry (AG) and also including relative gravimetry (RG) and GPS measurements.
ISSN: 0264-3707

hal-00456035
https://hal.archives-ouvertes.fr/hal-00456035
DOI : 10.1016/j.jog.2009.09.004

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Reef positions record the interaction between eustasy and tectonics, and have been used worldwide to characterize vertical deformations of upper-plates at different time-scales and constrain the seismic behavior of megathrusts. Along the Lesser Antilles volcanic arc, high-resolution marine geophysical data were collected on the 2–20 km wide eastern Martinique reef platform to reconstruct its stratigraphic and morphologic history, and understand the influence of local normal faulting, volcanism and plate-scale subduction processes on Holocene and Late Pleistocene reef development. The subsiding Martinique platform's stratigraphy is composed of multiple superimposed sea-level highstand deposits separated by subaerial exposure surfaces of sea-level low stands. The carbonate platform consists of two laterally-extensive carbonate units (unit U2 overlying unit U3) that extend to the platform edge to a depth of − 95 m MSL (mean sea level), and form two morphologic terraces, M2 and M3 respectively. The landward portion of unit U2 is partially overlain between 0 and − 60 m MSL by the living reef tract U1. The current reef is composed of a landward fringing reef, a lagoon and a seaward barrier reef, the latter forming a double-bank barrier around the Caravelle Peninsula. In near-shore multi-channel seismic profiles, a distinct reflector at ~− 35 m MSL, probably a subaerial exposure surface E1, separates the reef sequence formed during the last transgression from a Pleistocene fossil reef tract forming unit U2. Offshore of Mount Pelée volcano (Late Pleistocene), the Holocene reef did not develop above unit U2, whose upper surface is incised by channels and apparent sinkholes. During the Holocene transgression, the possibility of excessive turbidity due to volcanic activity may have inhibited reef development in this area. The un-dated unit U2 probably developed 120–130 ka ago during the last interglacial (MIS 5.5) + 6 m MSL highstand as thick, extensive reefs deposited all along the Lesser Antilles arc. Due to subsidence, MIS 5.5 reefs are not represented by onshore facies, except along the southern Sainte Anne Peninsula where normal faulting and uplift balances island-scale subsidence. Based on unit U2's present elevation and assuming an MIS 5.5 age and + 6 m MSL sea level, Martinique has subsided at maximum 0.3 m/ky, likely due to subduction processes that question the coupling state of the megathrust.
ISSN: 0025-3227

hal-01307036
https://hal.archives-ouvertes.fr/hal-01307036
DOI : 10.1016/j.margeo.2015.08.001

Éditeur(s) : HAL CCSD Geological Society
Résumé : International audience
An integrated stratigraphic study was conducted on the shallow water carbonate platforms of the Guadeloupe archipelago to refine the tectonic evolution of the Lesser Antilles forearc. The carbonate platforms are now dated to the Zanclean-Calabrian interval, and their demise occurred between 1.5 and 1.07 Ma. The precise chronostratigraphy allows dating of the main extensional tectonic events since the late Miocene. An initial episode occurred during the late Miocene, related to the reactivation of inherited N130°E-trending shear zones, and led to the emergence of most parts of the forearc. Subsequently, Zanclean to early Piacenzian carbonate platforms developed in association with a general subsidence of the forearc. During the late Piacenzan, a second extensional episode occurred. At this time La Désirade underwent major uplift and emergence whereas most of the forearc remained submerged. Prior to 1.07 Ma, a third north-south extensional episode occurred and led to the final demise of the carbonate platforms. Thus the forearc was characterized by general subsidence since the early Pliocene interrupted by three main extensional episodes and related differential uplifts. This suggests that the Lesser Antilles subduction is probably erosive north of latitude 15°N since c. 5 Ma, related to aseismic ridge subduction.
ISSN: 0016-7649

hal-01053696
https://hal.archives-ouvertes.fr/hal-01053696
DOI : 10.1144/jgs2013-005