Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In the Tahalgha district (southwestern Hoggar, Algeria), the Cenozoic volcanism has sampled subcontinental mantle beneath two crustal terranes that collided during the Pan-African orogeny: the “Polycyclic Central Hoggar” to the east and the “Western Hoggar” to the west. Two major lithospheric shear zones separate these terranes: the “4°35” and the “4°50” faults. Mantle xenoliths were collected between the two faults and across the 4°35 fault. In addition to a range in equilibrium temperatures and chemical compositions reported elsewhere, the samples show variations in their microstructures and crystallographic preferred orientations. Equilibrium temperatures and geochemical characteristics allow dividing them into low — (LT; 700–900 °C), intermediate — (IT; 900–1000 °C), and high-temperature (HT; 1000–1100 °C) xenoliths. The LT and IT peridotites occur on both sides of the 4°35 fault; they are usually coarse-grained. HT xenoliths are present only east of the 4°35 fault, in the narrow domain stuck between the two faults; they are fine-grained and extensively affected by annealing and melt–rock reactions. Microstructures and crystallographic textures indicate that deformation in the LT- and IT-xenoliths occurred through dislocation creep under relatively high-temperature, low-pressure conditions, followed by post-kinematic cooling. The fine-grained HT-xenoliths were deformed under relatively high-stress conditions before being annealed.Combining microstructural and CPO data with petrological and geochemical informations suggests that: (1) the LT xenoliths are remnants of the Neoproterozoic lithospheric mantle that preserved microstructural and chemical characteristics inherited from the Pan-African orogeny, and (2) the HT xenoliths record localized Cenozoic deformation associated with melt channeling through feed-back processes that culminated in the formation of high-permeability porous-flow conduits. Limited grain-growth in HT xenoliths suggests that advective heating of melt conduits was transient and rapidly followed by thermal relaxation due to conductive heat loss into wall-rock peridotites represented by the IT xenoliths, then by exhumation due to volcanic activity.
ISSN: 0040-1951

hal-01171761
https://hal.archives-ouvertes.fr/hal-01171761
DOI : 10.1016/j.tecto.2014.11.012

Éditeur(s) : HAL CCSD [London] : Nature Pub. Group Nature Publishing Group
Résumé : International audience
The deeply eroded West Gondwana Orogen is a major continental collision zone that exposes numerous occurrences of deeply subducted rocks, such as eclogites. The position of these eclogites marks the suture zone between colliding cratons, and the age of metamorphism constrains the transition from subduction-dominated tectonics to continental collision and mountain building. Here we investigate the metamorphic conditions and age of high-pressure and ultrahigh-pressure eclogites from Mali, Togo and NE-Brazil and demonstrate that continental subduction occurred within 20 million years over at least a 2,500-km-long section of the orogen during the Ediacaran. We consider this to be the earliest evidence of large-scale deep-continental subduction and consequent appearance of Himalayan-scale mountains in the geological record. The rise and subsequent erosion of such mountains in the Late Ediacaran is perfectly timed to deliver sediments and nutrients that are thought to have been necessary for the subsequent evolution of sustainable life on Earth.
ISSN: 2041-1723

hal-01122789
https://hal.archives-ouvertes.fr/hal-01122789
DOI : 10.1038/ncomms6198

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
ISSN: 0264-3707

hal-00680683
https://hal-brgm.archives-ouvertes.fr/hal-00680683
DOI : 10.1016/j.jog.2011.11.010

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This paper provides a synthesis of current data and interpretations on the crustal structure of the Pyrenean-Cantabrian orogenic belt, and presents new tectonic models for representative transects. The Pyrenean orogeny lasted from Santonian (~84 Ma) to early Miocene times (~20 Ma), and consisted of a spatial and temporal succession of oceanic crust/exhumed mantle subduction, rift inversion and continental collision processes at the Iberia-Eurasia plate boundary. A good coverage by active-source (vertical-incidence and wide-angle reflection) and passive-source (receiver functions) seismic studies, coupled with surface data have led to a reasonable knowledge of the present-day crustal architecture of the Pyrenean-Cantabrian belt, although questions remain. Seismic imaging reveals a persistent structure, from the central Pyrenees to the central Cantabrian Mountains, consisting of a wedge of Eurasian lithosphere indented into the thicker Iberian plate, whose lower crust is detached and plunges northwards into the mantle. For the Pyrenees, a new scheme of relationships between the southern upper crustal thrust sheets and the Axial Zone is here proposed. For the Cantabrian belt, the depth reached by the N-dipping Iberian crust and the structure of the margin are also revised.The common occurrence of lherzolite bodies in the northern Pyrenees and the seismic velocity and potential field record of the Bay of Biscay indicate that the precursor of the Pyrenees was a hyperextended and strongly segmented rift system, where narrow domains of exhumed mantle separated the thinned Iberian and Eurasian continental margins since the Albian-Cenomanian. The exhumed mantle in the Pyrenean rift was largely covered by a Mesozoic sedimentary lid that had locally glided along detachments in Triassic evaporites. Continental margin collision in the Pyrenees was preceded by subduction of the exhumed mantle, accompanied by the pop-up thrust expulsion of the off-scraped sedimentary lid above. To the west, oceanic subduction of the Bay of Biscay under the North Iberian margin is supported by an upper plate thrust wedge, gravity and magnetic anomalies, and 3D inclined sub-crustal reflections. However, discrepancies remain for the location of continent-ocean transitions in the Bay of Biscay and for the extent of oceanic subduction. The plate-kinematic evolution during the Mesozoic, which involves issues as the timing and total amount of opening, as well as the role of strike-slip drift, is also under debate, discrepancies arising from first-order interpretations of the adjacent oceanic magnetic anomaly record.
ISSN: 0040-1951

insu-01683989
https://hal-insu.archives-ouvertes.fr/insu-01683989
https://hal-insu.archives-ouvertes.fr/insu-01683989/document
https://hal-insu.archives-ouvertes.fr/insu-01683989/file/teixell-tectono-2018.pdf
DOI : 10.1016/j.tecto.2018.01.009

Éditeur(s) : HAL CCSD Himalayan Association Advance Science
Résumé : The Himalayas and the Tibetan Plateau are considered as the classical case of continental collision.
ISSN: 1727-5210

hal-00854401
https://hal.archives-ouvertes.fr/hal-00854401
DOI : 10.3126/hjs.v5i7.1267

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : The Zagros Simply Folded Belt (ZSFB) is an active fold-and-thrust belt resulting from the still continuing continental collision between the Arabian plate and the Iranian plate, which probably started in the Oligocene. The present-day shortening (N25°) is well documented by focal mechanisms of earthquakes and global positioning system (GPS) surveys. We propose in this study a comparison of published palaeostress markers, including magnetic fabric, brittle deformation and calcite twinning data. In addition, we describe the magnetic fabric from Palaeocene carbonates (10 sites) and Mio-Pliocene clastic deposits (15 sites). The magnetic fabrics are intermediate, with magnetic foliation parallel to the bedding, and a magnetic lineation mostly at right angles to the shortening direction. This suggests that the magnetic fabric retains the record of an early layer-parallel shortening (LPS) that occurred prior to folding. The record of LPS allows the identification of originally oblique folds such as the Mand Fold, which have developed in front of the Kazerun Fault. The shape parameter of the magnetic fabric indicates a weak strain compatible with the development of detachment folds in the ZSFB. The palaeostress datasets, covering the Palaeocene to Pleistocene time interval, support several folding episodes accompanied by a counter-clockwise rotation of the stress field direction. The Palaeocene carbonates in the ZSFB record a N47 LPS during early to middle Miocene detachment folding in the High Zagros Belt (HZB). The Mio-Pliocene clastic deposits recorded a N38 LPS prior to and during detachment folding within the ZSFB at the end of the Miocene-Pliocene. Similarly, fault slip and calcite twin data from the ZSFB also support a counter-clockwise rotation from NE to N20 between the pre-folding stage and the late rejuvenation of folds. This counter-clockwise trend of palaeostress data agrees with fault slip data from the HZB. During the late stage of folding in the ZSFB, the Plio-Quaternary palaeostress trends are consistently parallel to the present-day shortening direction.
Tectonic and stratigraphic evolution of Zagros and Makran during the Mesozoic-Cenozoic

hal-00545036
https://hal.archives-ouvertes.fr/hal-00545036
DOI : 10.1144/SP330.6

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Oisans Massif, located in the external zones of the western Alps, experienced significant shortening during the Alpine collision. While a series of major top-to-the west shear zones was recently described, the general low grade of the metamorphism has not attracted much petrological and geochronological studies. This paper provides combined temperature and age constraints on the evolution of the Oisans Massif. Temperature was estimated with the Raman Spectrometry of Carbonaceous Material (RSCM) method and chlorite geothermometry. Maximum temperature reached by the Mesozoic cover (Tmax) from Grenoble to the Galibier pass (E-W) and from Saint Jean de Maurienne to Embrun (N-S) yielded almost constant ca. 330 °C temperatures all through the Massif. Temperatures however strongly decrease either westward towards the top of the Vercors sedimentary sequence or eastward towards the Penninic Frontal Thrust. Age constraints were retrieved using 40Ar/39Ar in situ analyses performed on variously strained samples from Alpine shear zones. Over strain gradients, incipient Alpine recrystallizations progressively develop at the expense of former Variscan parageneses. A combined textural and EPMA approach permitted to identify newly formed chlorite and phengite that unequivocally grew in response to deformation or to low grade metamorphism. Chlorites recorded temperatures from ca. 350–150 °C during the activity of shear zones. In parallel, 40Ar/39Ar in situ experiments enabled dating deformation using both synkinematic phengites crystallized below the closure temperature of white-micas and former Variscan muscovite whose isotopic system have been, at least partially re-opened. Activity of top-to-the-west shear zones responsible for the shortening and thickening of the Oisans massif thus occurred between 34 and 33 and 25 Ma. Integrating these new age-constraints, Tmax estimates, and published geological data on the Oisans Massif and neighbouring areas allow proposing a new shortening scenario for the external zones. From ca. 34–33 Ma, the Oisans Massif was buried as a rigid block below more internal units and reached a temperature of ca. 330 °C. Shearing progressively localized along a series of top-to-the-W shear zones in the basement until 25 Ma. Deformation then localized along a major thrust at the base of the ECM massif and propagated along the basement-cover interface below the Vercors massif after 16 Ma.
ISSN: 0264-3707

Droits : info:eu-repo/semantics/OpenAccess
insu-01093878
https://hal-insu.archives-ouvertes.fr/insu-01093878
https://hal-insu.archives-ouvertes.fr/insu-01093878/document
https://hal-insu.archives-ouvertes.fr/insu-01093878/file/GEOD1326RA.pdf
DOI : 10.1016/j.jog.2014.09.004

Éditeur(s) : HAL CCSD
Résumé : National audience
Crustal-scale models for the Pyrenees based on ECORS reflection profileshave around 20 years now. In recent years, new understandingswere gained on the reconstruction to the preorogenic times, namelya scenario of extreme crustal attenuation and mantle exhumation ; inturn, this has implications on the interpretation of the present-day structure,as new models for the chain must consider feedbacks between themid-Cretaceous hyperextension and the Pyrenean inversion. On the WcentralPyrenean traverse, the southern part comprises 3 S-vergent basementthrust units, the Lakora, Gavarnie and Guarga units, flanked by thedetached cover of the Jaca piggyback basin and the Ebro basin, wherethe Mesozoic is thin and Late Cretaceous-Tertiary synorogenic carbonateand detrital sequences record a southward depocenter migration.To the N, the Chaînons Béarnais belt (CB) is a system of Jurassic to LowerCretaceous carbonate anticline ridges separated by synclines withthick Albian-Cenomanian flysch, covered to the north by Upper Cretaceousflysch sequences. The CB is thrust southwards together with theLakora thrust unit and northwards onto the Aquitaine basin. CB foldinglargely results from the rising and squeezing of diapirs initiated duringthe Jurassic-Early Cretaceous extension. Pieces of crust and mantle liftedin the diapirs attest that the CB derive from a Cretaceous domainof hyperextended continental crust and exhumed mantle. Moho reflectionsin the ECORS-Arzaq profile constrain the present deep structure.Restoration leads to a Mesozoic cover detachment over the N-Iberianand S-European margins. Inversion began by subduction of the exhumedmantle and folding and pop-up thrusting of the CB cover onto themargins. From the mid-late Eocene onwards, continental collision wasaccommodated by wedging and thrust stacking in the Iberian crust, involvingthe piggyback formation of S-vergent basement thrusts in theupper crust, and the northward subduction of the lower crust.
24 ème Réunion des sciences de la Terre 2014
Pau, France

insu-01080831
https://hal-insu.archives-ouvertes.fr/insu-01080831

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
To estimate the seismic hazard, the geometry (dip, length and orientation) and the dynamics (type of displacements and amplitude) of the faults in the area of interest need to be understood. In this paper, in addition to geomorphologic observations, we present the results of two ground penetrating radar (GPR) campaigns conducted in 2010 and 2011 along the Emeelt fault in the vicinity of Ulaanbaatar, capital of Mongolia, located in an intracontinental region with low deformation rate that induces long recurrence time between large earthquakes. As the geomorphology induced by the fault activity has been highly smoothed by erosion processes since the last event, the fault location and geometry is difficult to determine precisely. However, by using GPR first, a non-destructive and fast investigation, the fault and the sedimentary deposits near the surface can be characterized and the results can be used for the choice of trench location. GPR was performed with a 50 MHz antenna over 2-D lines and with a 500 MHz antenna for pseudo-3-D surveys. The 500 MHz GPR profiles show a good consistency with the trench observations, dug next to the pseudo-3-D surveys. The 3-D 500 MHz GPR imaging of a palaeochannel crossed by the fault allowed us to estimate its lateral displacement to be about 2 m. This is consistent with a right lateral strike-slip displacement induced by an earthquake around magnitude 7 or several around magnitude 6. The 2-D 50 MHz profiles, recorded perpendicular to the fault, show a strong reflection dipping to the NE, which corresponds to the fault plane. Those profiles provided complementary information on the fault such as its location at shallow depth, its dip angle (from 23 • to 35 •) and define its lateral extension. Central Asia is known for its high level of seismic hazards, especially Mongolia, which has been one of the most seismically active intracontinental regions in the world with four large earthquakes (magnitude around 8) along its active faults in the western part of the country during the last century (Khilko et al. 1985). The deformation in Mongolia is located between compressive structures related to the collision and penetration of the Indian plate into the Eurasian plate and extensive structures in the north of the country related with the Baykal rift (Tapponnier & Molnar 1979; Baljinnyam et al. 1993; Schlupp 1996; Bayasgalan & Jackson 1999). The seismic activity observed in the vicinity of Ulaanbaatar (UB), capital of Mongolia, is relatively low compared to the activity observed in western Mongolia. Nevertheless, since 2005, the seismic activity around UB not only has increased, but is also organized (see Fig. 1) at the west of UB along two perpendicular directions, which determine two active faults: Emeelt fault, discovered in 2008 (NNW-SSE direction, 25-km-long minimum and situated about 10 km W of UB) and Hustai fault (WSW–ENE direction, 80 km long, with its NE tip at less than 20 km west of UB); their length and morphology indicate that they can produce earthquakes of magnitude 6.5–7.5 (Schlupp et al. 2012). Most of the Mongolian population (1.2 million over 3 million) is concentrated at UB, which is the main political and economical centre of the country. Hence, the study of seismic hazard and the estimation of the probability of future destructive earthquakes are of primary importance for the country (Dugarmaa et al. 2006). Since the last large earthquake, the faults geomorphology has been highly smoothed by erosional processes and the exact location of the fault plane surface rupture is thus hidden within a several metre wide strip. The GPR method has been proven to give good and useful results to characterize faults by identifying offsets of radar reflections (Malik et al. 2007; Christie et al. 2009; Yalçiner et al. 2013) and
ISSN: 0956-540X

hal-01342629
https://hal.archives-ouvertes.fr/hal-01342629
https://hal.archives-ouvertes.fr/hal-01342629/document
https://hal.archives-ouvertes.fr/hal-01342629/file/Dujardin_Bano_etal_Geoph.%20J.%20Int._2014_final.pdf
DOI : 10.1093/gji/ggu130

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The strike-slip faults of north Tibet accommodate part of the Cenozoic convergence between India and Asia. Along the Karakax valley south of Yecheng and near the Xidatan trough south of Golmud, the active traces of the Altyn-Tagh and Kunlun faults follow narrow belts of metamorphic rocks. The deformation recorded in those mylonites is sinistral strike-slip. Rb/Sr and 40Ar/39Ar ages of deformation from syntectonic fabrics formed at 350–400°C 120 Ma. Argon loss suggests that deformation was associated to a 250–300°C thermal pulse that lasted 5–20 Ma after the onset of movement. Unroofing occurred much later, around 25 Ma when sudden cooling suggests a component of thrusting or more likely normal faulting. The Cretaceous shear may be related to collision between the Qiantang and the Lhasa blocks. The Karakax and Xidatan shear zones may have formed a unique, continuous boundary in the Cretaceous, which was later reused by the Tertiary strike-slip faults, leading to potentially calculable offsets along the Altyn-Tagh fault.
ISSN: 2169-9313

hal-00197562
https://hal.archives-ouvertes.fr/hal-00197562
https://hal.archives-ouvertes.fr/hal-00197562/document
https://hal.archives-ouvertes.fr/hal-00197562/file/Arnaud_JGR000904_def.pdf
DOI : 10.1029/2001JB000904

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
The processes active in the deep crust above an oceanic subduction zone during its evolution have been constrained through a detailed geochemical study (major and trace elements and Sr, Nd and Pb isotopes) of representative samples through an 30 km thick exhumed crustal section of the Cretaceous Kohistan oceanic island arc (Northern Pakistan). The use of both trace elements and radiogenic isotopes reveals two distinct geochemical suites (suites A and B) within the JijalPatanKiruKamila (JPKK) complex. Suite A is characterized by a progressive enrichment in Pb-207 and a decrease in Nd-143/Nd-144 with increasing La-N/Sm-N. Suite B has higher Pb-207/Pb-204 and lower Nd-143/Nd-144 ratios with approximately constant La-N/Sm-N. By combining trace elements with different partitioning behaviour it is demonstrated that there is an increasing contribution of the subduction component in the magmas with time. It is also possible to distinguish a slab component imprint carried by aqueous fluids from one corresponding to sediment melts. Intrusive granites are abundant in the upper levels of the JPKK section. All were generated at the arc root level (Jijal crustal section) during dehydration-melting of hornblende-rich plutonic rocks. A three-stage geodynamic model is proposed for the evolution of the arc over a period of 30 Myr. The first stage (117105 Ma) starts with the onset of subduction, which was followed by the building of the volcanic arc. The second stage (10599 Ma to 9691 Ma) corresponds to a major igneous event, which was characterized by abundant magma underplating and granulite-facies metamorphism at the arc base. Recycling of the residualcumulative lower crust into the convective asthenospheric mantle was efficient during this stage, and was probably related to thermo-mechanical erosion of the base of the crust. The last stage (9585 Ma) corresponds to a period of low magmatic activity, which marked the end of the intra-oceanic subduction. This is related to the formation of a cold blanket above the slab surface as a result of thermo-mechanical erosion of the cold walls of the subduction zone (i.e. the upper part of the slab and the base of the overriding plate), and corner flow dragging the cold material into the zone of melt generation. Ultimately, a voluminous magmatic pulse occurred around 85 Ma (forming the Chilas complex), before arccontinent collision.
ISSN: 0022-3530

hal-00420068
https://hal.archives-ouvertes.fr/hal-00420068
DOI : 10.1093/petrology/egp010

Éditeur(s) : HAL CCSD Geological Society
Résumé : International audience
A polyphase history of oceanic construction and consumption is documented by the distribution of the Tethyan ophiolitic suture zones in Iran. Despite the geodynamic significance of these suture zones, few modern petrological and geochronological data are available from these ophiolitic domains, hampering a full assessment of the timing, thermobaric regimes and palaeotectonic scenarios leading to oceanic suturing and continental assembly in Iran and, more in general, along the southern margin of Eurasia. In this paper, we describe a newly discovered HP ophiolite mélange within the Rasht ophiolites, at the NW termination of the Palaeo-Tethyan suture in Iran. Petrological investigations on the metamorphic units embedded within the ophiolite mélange are integrated with whole-rock geochemistry and Ar–Ar phengite geochronology to constrain the geotectonic setting of formation and to define the associated P–T–t paths. We provide evidence that the Rasht ophiolite domain corresponds to an exhumed subduction complex formed during Early Carboniferous (c. 350 Ma) subduction of a branch of the Palaeo-Tethyan oceanic realm, with peak metamorphism equilibrated under blueschist- to eclogite-facies metamorphic conditions. Implications of these data for the palaeotectonic reconstruction during closure of the Palaeo-Tethyan ocean and the terminal collisional assembly along the southern margin of the Eurasia plate are also discussed.
ISSN: 0016-7649

hal-01571998
https://hal.archives-ouvertes.fr/hal-01571998
DOI : 10.1144/jgs2016-130

Éditeur(s) : HAL CCSD
Résumé : International audience
At the time of the collision with India (55Ma), the southern margin of Asia was a composite continental domainresulting from an already long history of successive accretions of different terranes having different rheologies.Knowledge about the structure, composition and thermal state of the Tibetan lithosphere through time is thusfundamental to understand the respective contributions of pre-Cenozoïc and Cenozoïc tectonics in the building ofthe Plateau to its present-day elevations.We focused on the boundary between the Qiangtang terrane to the south, and the Songpan-Ganze terrane to thenorth.We jointly studied deep crustal xenoliths and associated (ultra-)potassic magmatism from the Eocene basinsof Nangqian and Xialaxiu (Qinghai Province, China), north of the Qiangtang terrane. The aims were to retrievethe composition and the thermal state of the lower crust during Eocene times, to study the behavior of the lowercrust and lithospheric mantle of the Eastern Qiangtang terrane and the adjacent Songpan-Ganze terrane at the timeof the collision, and the link with the magmatic activity.Crustal xenoliths are of two types: biotite-rich, amphibole bearing metasediments; and garnet-bearing quartzofeldspathicgneisses. Such assemblages are typical of very high-grade amphibolite and granulite faciesmetamorphism; further study should allow us to quantify the pressures and temperatures those rocks experienceduntil the time they were sampled by their host lavas.Major element geochemistry places the c.a. 51-49 Ma (Spurlin et al., 2005) Xialaxiu volcanic field in a fairlydifferentiated (SiO265-70 wt%) high-K field of the calc-alcaline series. Trace element analysis suggests a strongcrustal contamination of the primary mantellic melts. C.a. 38-37 Ma (Spurlin et al., 2005) Nangqian magmaticbodies span across the alkaline series, with high to extreme (K2O6wt%) values. Complex major and traceelement patterns, coupled with high-resolution microprobe data on pyroxene xenocrysts, suggest that enrichmentoccurred at the source by metasomatism of the lithospheric mantle.Further work will precise which mechanisms could have accounted for such a metasomatism of the mantle beneaththe Northern Qiangtang terrane during Eocene, and whether the lower crust had an autochtonous or allochtonousnature.
Geophysical Research Abstracts
Vienne, Austria

insu-01308919
https://hal-insu.archives-ouvertes.fr/insu-01308919

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
In the Tifnoute Valley, three plutonic units have been defined: the Askaoun intrusion, the Imourkhssen intrusion and the Ougougane group of small intrusions. They are made of quartz diorite, granodiorite and granite and all contain abundant mafic microgranular enclaves (MME). The Askaoun granodiorite and the Imourkhssen granite have been dated by LA-ICP-MS on zircon at 558 ± 2 Ma and 561 ± 3 Ma, respectively. These granitic intrusions are subcontemporaneous to the widespread volcanic and volcano-detrital rocks from the Ouarzazate Group (580-545 Ma), marking the post-collisional transtensional period in the Anti-Atlas and which evolved towards alkaline and tholeiitic lavas in minor volume at the beginning of the Cambrian anorogenic intraplate extensional period. Geochemically, the Tifnoute Valley granitoids belong to an alkali-calcic series (high-K calc-alkaline) with typical Nb-Ta negative anomalies and no alkaline affinities. Granitoids and enclaves display positive εNd-560Ma (+0.8 to +3.5) with young Nd-TDM between 800 and 1200 Ma and relatively low 87Sr/86Sr initial ratios (Sri: 0.7034 and 0.7065). These values indicate a mainly juvenile source corresponding to a Pan-African metasomatized lithospheric mantle partly mixed with an old crustal component from the underlying West African Craton (WAC). Preservation in the Anti-Atlas of pre-Pan-African lithologies (c. 2.03 Ga basement, c. 800 Ma passive margin greenschist-facies sediments, allochthonous 750-700 Ma ophiolitic sequences) indicates that the Anti-Atlas lithosphere has not been thickened and was never an active margin during the Neoproterozoic. After a transpressive period, the late Ediacaran period (580-545 Ma) is marked by movement on near vertical transtensional faults, synchronous with the emplacement of the huge Ouarzazate Group and the Tifnoute Valley granitoids. We propose here a geodynamical model where the Tifnoute Valley granitoids as well as the Ouarzazate Group were generated during the post-collisional metacratonic evolution of the northern boundary of the West African craton. The convergence with the peri-Gondwanan active margin produced brittle fracturing of the cratonic boundary without thickening, allowing rising of magmas. The Tifnoute Valley granitoids display a metasomatized lithospheric mantle source mixed with a minor ancient (2 Ga) continental crust component from the underlying WAC.
ISSN: 0930-0708

halsde-00782152
https://hal.archives-ouvertes.fr/halsde-00782152
DOI : 10.1007/s00710-012-0245-3

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Gibraltar arc, spans a complex portion of the Africa-Eurasia plate boundary marked by slow oblique convergence and intermediate and deep focus seismicity. The seemingly contradictory observations of a young extensional marine basin surrounded by an arcuate fold-and-thrust belt, have led to competing geodynamic models (delamination and subduction). Geophysical data acquired in the past decade provide a test for these models and support a narrow east-dipping, subduction zone. Seismic refraction studies indicate oceanic crust below the western Gulf of Cadiz. Tomography of the upper mantle reveals a steep, east-dipping high P-wave velocity body, beneath Gibraltar. The anisotropic mantle fabric from SKS splitting shows arc-parallel "fast directions", consistent with toroidal flow around a narrow, westward retreating subducting slab. The accompanying WSW advance of the Rif-Betic mountain belt has constructed a thick pile of deformed sediments, an accretionary wedge, characterized by west-vergent thrust anticlines. Bathymetric swath‐mapping images an asymmetric embayment at the deformation front where a 2 km high basement ridge has collided. Subduction has slowed significantly since 5 Ma, but deformation of recent sediments and abundant mud volcanoes suggest ongoing activity in the accretionary wedge. Three possible origins for this deformation are discussed; gravitational spreading, overall NW-SE convergence between Africa and Iberia and finally a WSW tectonic push from slow, but ongoing roll-back subduction. In the absence of arc volcanism and shallow dipping thrust type earthquakes, evidence in favor of present-day subduction can only be indirect and remains the object of debate. Continued activity of the subduction offers a possible explanation for great (M > 8.5) earthquakes known to affect the area, like the famous 1755 Great Lisbon earthquake. Recent GPS studies show SW motion of stations in N Morocco at velocities of 3-6 mm/yr indicating the presence of an independent block, a "Rif-Betic-Alboran" microplate, situated between Iberia and Africa.
ISSN: 0040-1951

insu-00769762
https://hal-insu.archives-ouvertes.fr/insu-00769762
DOI : 10.1016/j.tecto.2012.08.038

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Field study, thermochronology and geochemistry of the east Lungmu Co (LMC) range highlight some of the geological events that shaped western Tibet. The LMC fault zone has long been interpreted as the boundary between the Tianshuihai terrane of Laurasian affinity and the Qiangtang block of Gondwanian affinity. In the LMC range, the Paleozoic series is intruded by the Mangtsa leucogranite whose zircon have a U/Pb age of 116.9 ± 1 Ma and by mafic rocks with U/Pb zircon ages ranging from 116.9 ± 1 to 95.1 ± 1.7 Ma. Geochemistry of the mafic rocks indicates that they have been emplaced in a supra-subduction zone setting, probably the north dipping Nujiang suture zone. 40Ar/39Ar micas ages of the granite indicate that cooling below ~ 350 °C occurred between 105 and 85 Ma. 40Ar/39Ar K-feldspar data suggest a fast cooling event at 60-55 Ma, which we relate to the reactivation of the LMC suture zone as a thrust at the onset of the India-Eurasia collision. The last, and still active, deformation event corresponds to left-lateral strike-slip faulting along the ENE-WSW LMC fault.
ISSN: 1342-937X

hal-00660491
https://hal.archives-ouvertes.fr/hal-00660491
DOI : 10.1016/j.gr.2011.07.026

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Souttoufide belt is situated between the High-Atlas in the north, the Mauritanides in the south and the West African Craton as well as the Tindouf basin in the east. Thus, this belt is a part of the West African fold belt system which surrounds the West African Craton. Outcrops occur only in three areas, while the rest of the Souttoufide belt is covered by Meso- to Cenozoic sediments. These areas are, from the south to the north, the Adrar Souttouf Massif, the Smara Zemmour area, and the western part of the Anti-Atlas. Because of the continuing processing and numerous publications, the Anti-Atlas cannot be dealt with in detail. Fundamental geological work in both of the other areas was mainly done during the second third of the 20th century, followed by several decades of inactivity. Numerous studies were done in the Adrar Souttouf massif during the last decade, while the Smara-Zemmour area still remains poorly investigated. Most of them were focused on geochronological analyses and geochemistry. Accordingly, the obtained data led to a new interpretation. The Adrar Souttouf is interpreted as a Pan-African belt exhibiting a Neoproterozoic island arc reworked by the Variscan collision between the North American Craton (NAC) and the West African Craton (WAC). The Smara-Zemmour area is considered as the external part of this Variscan belt thrusted onto the Palaeozoic Tindouf basin. The western Anti-Atlas as considered as a Pan-African active margin reworked during the Variscan orogen. Together, these three areas, lead to the hypothesis of a Late Pan-African belt capped by the Early and Middle Palaeozoic covers and then affected by the Middle Carboniferous tectonic event (330 Ma) related to the Pangaean assembly. Correlations with adjacent belts (Mauritanides and Anti-Atlas) are considered.
ISSN: 0899-5362

hal-01382815
https://hal.archives-ouvertes.fr/hal-01382815
DOI : 10.1016/j.jafrearsci.2015.04.016

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
Located east of Guadeloupe, the island of La Désirade exhibits the oldest rocks of the Lesser Antilles arc and the eastern Caribbean plate. An old magmatic basement is composed of (1) late Jurassic ophiolitic complex with meta-basaltic pillow lavas and interbedded radiolarites, (2) acid igneous complex comprising meta-quartz-diorite and meta-rhyolitic lavas flows, and (3) meta-diabasic/microdioritic dyke swarm complex. We present and discuss the discovery of synmetamorphic thrust tectonics in this island. Based on detailed structural analysis we evidenced two main compressive events. The first event (D1) is characterized by pervasive folding associated with thrust development. In the northeastern part of the island, a major thrust fault, the Grand Abaque Thrust, has been discovered which displaces for several kilometers the acid igneous complex onto the ophiolitic unit. The second deformation event (D2) is featured by a main pervasive cleavage S2 observed at the regional scale associated with upright folding (F2) and by the development of two sets of conjugated steeply dipping strike-slip shear zones, dextral 130°N and sinistral 20°N striking, respectively. Microstructural observations indicate that Greenschist facies metamorphism is clearly contemporaneous with the development of D1 and D2 superimposed tectonic structures. Ar/Ar geochronology was performed on two bulk of adularia minerals sampled in the northeast volcanic complex within a deformed zone related to a D2 event. These analyses yield well-defined and concordant plateau ages at 106.2 ± 1.7 Ma and 107.2 ± 1.8 Ma. Thus, shortening and thickening tectonics occurred during Lower Cretaceous (Albian). In the available framework of Caribbean geodynamics, the synmetamorphic thrust tectonics we discovered in the French Lesser Antilles is related to the collision between an Aptian-Albian oceanic plateau and the Andean-Cordilleran east-dipping subduction zone. Our results support subduction polarity reversal during Lower Cretaceous.
ISSN: 0278-7407

hal-00620555
https://hal.archives-ouvertes.fr/hal-00620555
DOI : 10.1029/2011TC002875

Éditeur(s) : HAL CCSD Springer Verlag (Germany)
Résumé : International audience
A hybrid linear ion-trap Fourier-transform ion cyclotron resonance mass spectrometer was used for top-down characterization of the abundant human salivary Cystatins, including S, S1, S2, SA, SN, C, and D, using collisionally activated dissociation (CAD) after chromatographic purification of the native, disulfide intact proteins from saliva. Post-translational modifications and protein sequence polymorphisms arising from single nucleotide polymorphisms (SNPs) were assigned from precursor and product ion masses at a tolerance of 10 ppm allowing confident identification of individual intact mass tags. Cystatins S, S1, S2, SA and SN were cleaved of a N-terminal 20 amino-acid signal peptide, and Cystatin C a 26-residue peptide, to yield a generally conserved N-terminus. In contrast, Cystatin D isoforms with 24 and 28 amino-acid residue N-terminal truncations were found such that their N-termini were not conserved. Cystatin S1 was phosphorylated at Ser3, while S2 was phosphorylated at Ser1 and Ser3 of the mature protein, in agreement with previous work. Both Cystatin D isoforms carried the polymorphism C46R (SNP: rs1799841). The 14328 Da isoform of Cystatin SN previously assigned with polymorphism P31L due to a SNP (rs2070856) was found only in whole saliva. Parotid secretions contained no detectable Cystatins while whole saliva largely mirrored the contents of submandibular/sublingual (SMSL) secretions. Top-down high-resolution mass spectrometry is a powerful tool for the identification and characterization of potential protein biomarkers in saliva.
ISSN: 1044-0305

hal-00677483
https://hal.archives-ouvertes.fr/hal-00677483
DOI : 10.1016/j.jasms.2010.01.025

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
The Early Palaeozoic Orogen of SE China consists of three litho-tectonic elements, from top to bottom: a sedimentary Upper Unit, a metamorphic Lower Unit and a gneissic basement. The boundaries between these units are flat lying, south directed, ductile decollements. The lower one is coeval with an amphibolite facies metamorphism (M1). The belt is reworked by migmatite-granite domes, high-temperature metamorphism (M2) and granitic plutons related to post-orogenic crustal melting. We date here the syn-M1 ductile shearing at 453 +/- 7 Ma by U-Th/Pb method on monazite. Previous ages and our new
ISSN: 0954-4879

hal-00420901
https://hal.archives-ouvertes.fr/hal-00420901
https://hal.archives-ouvertes.fr/hal-00420901/document
https://hal.archives-ouvertes.fr/hal-00420901/file/Faureetal-TerraNova-2009.pdf
DOI : 10.1111/j.1365-3121.2009.00888.x