Éditeur(s) : HAL CCSD
Résumé : In SW Yukon – SE Alaska, the boundary between the Pacific and North America plates is characterized by a syntaxis at the transition between the Aleutian subduction to the W and the Fairweather – Queen Charlotte strike-slip faults to the SE. The relative motion is oblique to the main fault structures, and the area is marked by the Yakutat block collision. From the Chugach – Saint Elias mountains in the plate boundary zone (up to 6 000 m high) to the intraplate strike-slip faults, markers of the present-day deformation give information on its partition in the system.During my PhD, I first measure surface deformation using a dense GPS network, deployed up to 500 km inland the North America plate. After precise processing and corrections of transient effects in the area (postseismic and glacial isostatic rebound), a new residual velocity field is produced for the syntaxis area, from which I derive strain rates. Those data allow me to quantify the fault slip rates for Fairweather and southern Denali strike-slip faults, and to characterize a bi-modal deformation pattern: Along the plate boundary, the deformation is localized on large-scale structures (accretionary prism to the W, Fairweather to the E); In the syntaxis area, strain rates are the highest and the GPS data shows a diffuse intraplate deformation, similar to an indentor pattern. The Yakutat block seems to strongly drive the North America plate deformation.This indentor pattern induces strong lateral variations on the large intraplate faults: the Denali – Totschunda – Duke River system. In a second part, I realize a regional geomorphological study to characterize the role and slip rate of those faults. From very high-resolution Digital Elevation Models (~ 1 m), a detailed cartography is done. On the basis of fieldwork observations, I measure offsets of fluvial and glacial markers, which are sampled for dating. A dextral cumulative deformation is highlighted on the northern Denali Fault, where as all southern Denali is marked by vertical deformation. This study allows me to quantify new slip rates for the system Denali – Totschunda – Duke River, and to show the leading role of the Totschunda (~ 14 mm/a) and Duke River (~ 6 mm/a) faults, contrary to the Denali Fault (~ 1 mm/a) North of the syntaxis.The new tectonic model for the Yakutat collision provides an important case study for the understanding of indentor systems. The concomitance of a rigid-block deformation (to the West) and diffuse deformation (to the East), as well as the near-zero slip rate on the lithospheric-scale southern Denali Fault highlight the major control of boundary conditions and the structural heritage on the orogen deformation.
Au SO Yukon – SE Alaska, la frontière entre les plaques Pacifique et Nord-Amérique est marquée par une syntaxe à la transition entre la subduction des Aléoutiennes à l’O et le décrochement de Fairweather – Queen Charlotte au SE. Le mouvement relatif est oblique et la région est marquée par la collision du bloc Yakutat. De la chaine des Chugach – Saint Elias en frontière de plaque (jusqu’à 6 000 m d’altitude) aux grands décrochements intraplaque, les marqueurs de la déformation actuelle apportent des informations sur sa partition dans ce système.Au cours de cette thèse, je m’intéresse dans un premier temps à mesurer la déformation de surface à l’aide d’un réseau GPS dense, déployé jusqu’à 500 km à l’intérieur de la plaque Nord-Amérique. Après un travail minutieux de traitement des données et de correction des effets transitoires (rebond post-glaciaire et post-sismique), un champ de vitesses résiduelles robuste et inédit est produit au niveau de la syntaxe, dont je dérive des taux de déformation. Ces données me permettent de quantifier les vitesses de glissement les failles décrochantes de Fairweather et Denali au Sud, et également de caractériser une déformation bimodale : En frontière de plaques, la déformation est localisée sur les grandes structures (prisme d’accrétion à l’O, Fairweather à l’E) ; Au niveau de la syntaxe, les taux de déformation sont les plus importants et les données GPS mettent en évidence une déformation intraplaque diffuse, similaire à un champ attendu à l’aplomb d’un indenteur. Le bloc Yakutat semble donc contrôler fortement la déformation de la plaque Nord-Amérique.Ce champ de déformation induit des variations latérales fortes sur les grandes failles intraplaque : le système Denali-Totschunda-Duke River. Dans une seconde partie, je réalise une étude géomorphologique régionale pour caractériser le rôle et la vitesse de ces failles. À partir de Modèles Numériques de Terrain très haute résolution (~ 1 m), une cartographie de détail est réalisée. Puis une mission de terrain me permet de mesurer des décalages sur des marqueurs fluviatiles et glaciaires et collecter des échantillons pour les dater. Je mets en évidence une déformation cumulée dextre sur le segment Nord de la faille de Denali, alors que toute la partie Sud déforme verticalement la surface. Cette étude me permet de quantifier de nouvelles vitesses de failles sur le système Denali-Totschunda-Duke River, et de montrer le rôle prépondérant des failles de Totschunda (~ 14 mm/a) et Duke River (~ 6 mm/a) contrairement à la faille de Denali (~ 1 mm/a) au Nord de la syntaxe.Le nouveau modèle cinématique proposé pour la région de collision Yakutat permet d’apporter un nouvel exemple à la compréhension des systèmes d’indenteur. La concomitance d’une déformation de blocs (à l’Ouest) et diffuse (à l’Est), ainsi que l’absence de déformation sur la faille lithosphérique de Denali Sud met en évidence le contrôle majeur des conditions aux limites et de l’héritage structural dans la déformation des orogènes.
https://hal.archives-ouvertes.fr/tel-01241688

tel-01241688
https://hal.archives-ouvertes.fr/tel-01241688
https://hal.archives-ouvertes.fr/tel-01241688/document
https://hal.archives-ouvertes.fr/tel-01241688/file/manuscrit_anais_v2_optimise.pdf

Éditeur(s) : HAL CCSD Annual Reviews
Résumé : International audience
The record of the continental lithosphere is patchy and incomplete; no known rock is older than 4.02 Ga, and less than 5% of the rocks preserved are older than 3 Ga. In addition, there is no recognizable mantle lithosphere from before 3 Ga. We infer that there was lithosphere before 3 Ga and that ∼3 Ga marks the stabilization of blocks of continental lithosphere that have since survived. This was linked to plate tectonics emerging as the dominant tectonic regime in response to thermal cooling, the development of a more rigid lithosphere, and the recycling of water, which may in turn have facilitated plate tectonics. A number of models, using different approaches, suggest that at 3 Ga the volume of continental crust was ∼70% of its present-day volume and that this may be a minimum value. The continental crust before 3 Ga was on average more mafic than that generated subsequently, and this pre-3 Ga mafic new crust had fractionated Lu/Hf and Sm/Nd ratios as inferred for the sources of tonalite-trondhjemite-granodiorite and later granites. The more intermediate composition of new crust generated since 3 Ga is indicated by its higher Rb/Sr ratios. This change in composition was associated with an increase in crustal thickness, which resulted in more emergent crust available for weathering and erosion. This in turn led to an increase in the Sr isotope ratios of seawater and in the drawdown of CO2. Since 3 Ga, the preserved record of the continental crust is marked by global cycles of peaks and troughs of U-Pb crystallization ages, with the peaks of ages appearing to match periods of supercontinent assembly. There is increasing evidence that the peaks of ages represent enhanced preservation of magmatic rocks in periods leading up to and including continental collision in the assembly of supercontinents. These are times of increased crustal growth because more of the crust that is generated is retained within the crust. The rates of generation of continental crust and mantle lithosphere may have remained relatively constant at least since 3 Ga, yet the rates of destruction of continental crust have changed with time. Only relatively small volumes of rock are preserved from before 3 Ga, and so it remains difficult to establish which of these are representative of global processes and the extent to which the rock record before 3 Ga is distorted by particular biases.
ISSN: 0084-6597

hal-01622692
https://hal.archives-ouvertes.fr/hal-01622692
DOI : 10.1146/annurev-earth-063016-020525

Éditeur(s) : HAL CCSD
Résumé : International audience
Timor Island was at time considered as an example of "accretionary prism" linked to the collision between the Australian block and the Banda arc. However, its geological evolution is more complex. Five main superimposed structural units are distinguished in West Timor. The today structure is the result of three main tectonic events that occurred during the Late Oligocene, Late Early Pliocene and Late Pliocene-Early Pleistocene times, respectively. Our field investigations in the 1990 to 2000 decade completed with geochemical analyses and K-Ar datings (Jurassic and Miocene ages) of magmatism allow to precise the geodynamic evolution of Timor that can be summarized as follows: a first block was detached from Gondwana (unit 2) and drifted to the Asiatic margin until the Late Oligocene when it collided with the Asiatic active margin (unit 3). Then, the new block formed by both 2 and 3 units drifted to the south during the Miocene and the Early Pliocene until it collided with the Australian margin (ASM), by the Late Early Pliocene. Then, the Australian and Timor blocks moved together towards the North-North East during the Late Pliocene until they collided with the Banda fore-arc (unit 4). Later on (Pleistocene), Timor island was capped by the "autochthon" (unit 5) and then on (Quaternary?) by the Banda volcanic arc northward thrusted over the South Banda basin. Taking in consideration its close relationships with both the Australian plate and the Eurasian one. Timor may be considered as a key area for building this geodynamical scenario of Indonesia.
Bulletin Société Géologique de France

insu-00933548
https://hal-insu.archives-ouvertes.fr/insu-00933548
DOI : 10.2113/gssgfbull.184.6.569

Éditeur(s) : HAL CCSD The Company of Biologists
Résumé : International audience
The ability to produce sound has been known for decades inBalistidae. Sounds of many species have been recorded and a varietyof sound-producing mechanisms have been proposed, includingteeth stridulation, collision of the buccal teeth and movements of thefins. The best-supported hypothesis involves movements of thepectoral fin against the lateral part of the swimbladder, called adrumming membrane. In this study, we describe for the first time thesounds made by the blackbar triggerfish Rhinecanthus aculeatus,which are like short drum rolls with an average duration of 85 ms,193 Hz dominant frequency and 136 dB SPL level at 3 cm distance.The sounds are a series of pulses that result from alternate sweepingmovements of the right and left pectoral fins, which push a system ofthree scutes that are forced against the swimbladder wall. Pulses fromeach fin occur in consecutive pairs. High-speed videos indicate thateach pulse consists of two cycles. The first part of each cyclecorresponds to the inward buckling of the scutes, whereas the secondpart of the cycle corresponds to an apparent passive recoil of thescutes and swimbladder wall. This novel sound productionmechanism is probably found in many members of Balistidaebecause these peculiar scutes occur in other species in the family.Comparison of sound characteristics from fishes of different sizesshows that dominant frequency decreases with size in juveniles butnot in adults.KEY WORDS: Acoustic, Communication, Swimbladder
ISSN: 00220949

hal-01472506
https://hal-univ-perp.archives-ouvertes.fr/hal-01472506
DOI : 10.1242/jeb.146514

Éditeur(s) : HAL CCSD Seoul National University
Résumé : http://www.episodes.org/backissues/302/abstract2.htm
International audience
The Trans-North China Belt (TNCB) is a Paleoproterozoic collisional orogen (ca. 1.9-1.8 Ga) responsible for the amalgamation of the North China Craton. Detail field works in Lüliangshan, Hengshan, Wutaishan and Fuping massifs where the belt is well exposed, allow us to draw new tectonic map and crustal-scale cross sections. The available petrologic, radiometric, geochronologic data are integrated in a geodynamic evolution scheme for this orogen. The Low Grade Mafic Unit (LGMU) is interpreted as an ophiolitic nappe rooted in a suture zone located in the western part of the Lüliangshan. This ophiolitic nappe overthrusts to the SE upon the Orthogneiss-Volcanites Unit (OVU) that consists of a bimodal volcanicsedimentary series metamorphosed under amphibolite facies conditions intruded by calcalkaline orthogneiss. The OVU is a composite Neoarchean-Paleoproterozoic magmatic arc developed during two stages (ca. 2500 and 2100 Ma) upon a continental basement corresponding to the western extension of the Neoarchean Fuping massif. The OVU overthrusts to the SE the Fuping massif along the Longquanguan shear zone. This stack of nappe, coeval with an amphibolite facies metamorphism, is dated at ca 1880 Ma. Subsequently, the metamorphic series experienced a widespread migmatization at 1850 Ma and was intruded by post-orogenic plutons dated at 1800 Ma. The weakly to unmetamorphosed Hutuo Supergroup unconformably overlies the metamorphosed and ductilely deformed units (OVU and LGMU), but it is also involved in a second tectonic phase developed in subsurface conditions. These structural features lead us to question the ca 2090 Ma age attributed to the Hutuo supergroup. Moreover, in the Fuping massif, several structural and magmatic lines of evidence argue for an earlier orogenic event at ca 2100 Ma that we relate to an older west-directed subduction below the Fuping Block. The Taihangshan Fault might be the location of a possible suture zone between the Fuping Block and an eastern one. A geodynamic model, at variance with previous ones, is proposed to account for the formation of the TNCB. In this scheme, three Archean continents, namely from West to East, the Ordos, Fuping and Eastern Blocks are separated by the Lüliang and Taihang Oceans. The closure of the Taihang Ocean at ca 2100 Ma by westward subduction below the Fuping Block accounts for the arc magmatism and the 2100 Ma orogeny. The second collision at 1900-1880 Ma between the Fuping and Ordos blocks is responsible for the main structural, metamorphic and magmatic features of the Trans-North China Belt.
ISSN: 0705-3797

insu-00152972
https://hal-insu.archives-ouvertes.fr/insu-00152972
https://hal-insu.archives-ouvertes.fr/insu-00152972/document
https://hal-insu.archives-ouvertes.fr/insu-00152972/file/Episodes_TNCB_Faure_et_al.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Iranian plateau is a flat ~ 1.5–2 km high plateau thought to result from the collision between the Arabian and Eurasian plates since ~ 30 ± 5 Ma, and may represent a young analogue to the so far better studied Tibetan plateau. In order to constrain the exhumation history of the internal Zagros and of the Iranian plateau, we herein present apatite (U-Th)/He (AHe) and apatite (AFT) and zircon fission-track (ZFT) data on plutonic rocks from the Sanandaj–Sirjan Zone (SSZ), Urumieh–Dokhtar magmatic arc (UDMA), Central Iran and Kopet Dagh. Thermochronologic data show that the SSZ was exhumed early in the collision process (essentially before 25–20 Ma), with a likely acceleration of cooling during the late Eocene, from 0.04 to 0.3 mm/year. Results suggest that cooling of the internal Zagros migrated from the SSZ to the UDMA during a more mature stage of the continental collision, after ~ 17 Ma (i.e., coeval with the outward propagation of deformation and topography fronts in the external Zagros). Constant exhumation rates in the UDMA (~ 0.3 mm/year) suggest that no significant variation of erosion rates occurred since the onset of continental collision. In Central Iran, the overlap of ZFT, AFT and AHe ages from gneissic samples points to rapid cooling during the late Eocene (~ 42 °C/Myr), which is consistent with previous reports on the formation of Eocene metamorphic core-complexes.
ISSN: 0024-4937

hal-01115691
https://hal.archives-ouvertes.fr/hal-01115691
DOI : 10.1016/j.lithos.2014.07.021

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
This study investigates three-dimensional flow modes of orogenic plateaus by means of physical modeling. Experiments consist of shortening two contiguous lithospheres of contrasting strength, one being a weak plateau-type lithosphere and the other a strong craton-type lithosphere. The lateral boundaries are either totally confined or allow escape toward a lateral foreland on one side. Two synconvergence flow regimes are distinguished, which are governed by the balance between the gravity potential and the strength of the plateau crust and the resistance of its lateral foreland. The first regime implies transversal (orogen-normal) injection of plateau lower crust into the collision zone as a result of confinement of the plateau by an increasingly stiffer lateral boundary. As a precursor mechanism to channel flow, transversal injection responds to downward thickening of the plateau crust that is forcedly extruded into the orogenic wedge. The second regime is that of collapse-driven lateral escape of the plateau. This regime is established after a threshold is attained in the interplate coupling in the collision zone, which allows the gravity potential of the plateau to overcome the resistance of its lateral boundary. Under the collapse-driven escape regime (orogen parallel), such as that governing Tibet during the last 13 Ma, most of the convergence in the plateau and the top and rear of the collisional wedge is transformed into lateral flow and extension.
ISSN: 0148-0227

hal-01229107
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01229107
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01229107/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01229107/file/2015JB012110_revised.pdf
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01229107/file/SupplementaryMaterial_final.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Gulf of Cadiz spans the plate boundary between Africa and Eurasia west of the Betic–Rif mountain belt. A narrow east dipping subduction zone descends beneath the Gulf of Cadiz and the straits of Gibraltar. The deep crustal structure of the Gulf and the adjacent SW Iberian and Moroccan margins is constrained by numerous multi-channel seismic reflection and wide-angle seismic surveys. A compilation of these existing studies is presented in the form of depth to basement, sediment thickness, depth to Moho and crustal thickness maps. These structural maps image an E–W trending trough, with thin (< 10 km) crust beneath the Gulf of Cadiz. This trough is filled by an eastward thickening wedge of sediments, reaching a thickness of 10–15 km in the eastern Gulf. These sediments are tectonically deformed, primarily along a series of westward-vergent thrust faults and represent a 200–250 km wide accretionary wedge. The northern and especially the southern limits of the accretionary wedge are marked by sharp morphological lineaments showing evidence of recent deformation. These tectonic limits are situated in an internal position with respect to the Miocene deformation front (external Betic and Rif allocthons), which has been abandoned. At the western boundary of the accretionary wedge, near the adjacent Seine and Horseshoe abyssal plains, an E–W trending basement high (Coral Patch Ridge) can be seen indenting the deformation front in an asymmetric manner. Analog modeling is performed using granular materials accreted against a semicircular backstop (representing the basement of the Rif and Betic mountain belts). The modeling initially produces a symmetric, arcuate accretionary wedge. The ensuing collision of an oblique rigid indenter retards accretion on one side, resulting in an embayment and a locally steeper deformation front. The deformation pattern observed in morphology and high-resolution seismic profiles suggests the accretionary wedge and underlying subduction system is still active. The implications of active subduction for the source region of the 1755 Lisbon earthquake and the regional seismic hazard assessment are discussed.
ISSN: 0040-1951

hal-00424922
http://hal.univ-brest.fr/hal-00424922
http://hal.univ-brest.fr/hal-00424922/document
http://hal.univ-brest.fr/hal-00424922/file/Gutscher_09Tphys_rev.pdf
DOI : 10.1016/j.tecto.2008.11.031

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Estimating how topography is maintained provides insights into the different factors responsible for surface deformations and their relative roles. Here, we develop a new and simple approach to assess the degree of isostatic compensation of continental topography at regional scale from GOCE gravity gradients. We calculate the ratio between the radial gradient observed by GOCE and that calculated from topography only. From analytical and statistical formulations, simple relationships between this ratio and the degree of compensation are obtained under the Airy–Heiskanen isostasy hypothesis. Then, a value of degree of compensation at each point of study area can be easily deduced. We apply our method to the Alaska-Canada Cordillera and validate our results by comparison with a standard isostatic gravity anomaly model and additional geophysical information for this area. Both our GOCE-based results and the isostatic anomaly show that Airy–Heiskanen isostasy prevails for the Yukon Plateau whereas additional mechanisms are required to support topography below the Northwest Territories Craton and the Yakutat collision zone.
ISSN: 0956-540X

hal-01467540
https://hal.archives-ouvertes.fr/hal-01467540
https://hal.archives-ouvertes.fr/hal-01467540/document
https://hal.archives-ouvertes.fr/hal-01467540/file/cadioGJI2016.pdf
DOI : 10.1093/gji/ggw281

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In this contribution we present a reconstruction of the overall lithotectonic architecture, from inner zones to external ones, of the Paleoproterozoic Trans North China Orogen, within the North China Craton. Moreover, forward thermobarometrical modeling on a kyanite-bearing gneiss yields a reliable prograde P-T-t-D path. In addition, 40Ar/39Ar dating on rocks from distinct litho-tectonic units helps us to distinguish several tectono-metamorphic events during the orogenic development. Considering these results, we propose a geodynamic model involving three cratonic blocks, namely the Western, Fuping and Eastern Blocks, separated by two oceans, the Lüliang and Taihang Oceans. The opening of oceanic basins occurred around 2.2-2.3 Ga. After the westward subductions of oceanic lithosphere, the Trans-North-China Orogen was built up through a polyphase tectonic evolution within the period 1900-1800 Ma. The first event (D1) corresponded to the emplacement of lower and upper nappes herein called the Orthogneiss-and-Volcanites Unit (OVU) and the Low-Grade-and-Mafic Unit (LGMU), respectively. The syn-metamorphic D1 deformation (1880 ± 10 Ma) is characterized by a NW-SE stretching and mineral lineation with a top-to-the SE sense of shear. During ongoing compression of the thickening orogenic crust, a second deformation event D2 (1850 ± 10 Ma) was responsible for (1) syn-anatectic lateral flow and exhumation of the orogenic root and (2) folding of the middle and upper parts of the orogenic wedge that consequently acquired a fan-type geometry. The late D3 (1830 ± 10 Ma) and D4 (1810 ± 10 Ma) events are related to late-orogenic normal and strike-slip shearing, respectively. In our present state of knowledge, the Paleoproterozoic Trans-North China Orogen might be regarded as the assemblage of two continent-continent collisional belts, both of which are characterized by nappe stacking accommodated by top-to-the E/SE ductile shearing. Continental subduction, crustal thickening, partial melting of overthickened crust, exhumation of HP rocks and deposition of syn-orogenic detrital basins are typical features of modern collisional-type orogens.
ISSN: 0301-9268

Droits : info:eu-repo/semantics/OpenAccess
insu-00628119
https://hal-insu.archives-ouvertes.fr/insu-00628119
https://hal-insu.archives-ouvertes.fr/insu-00628119/document
https://hal-insu.archives-ouvertes.fr/insu-00628119/file/Trap-PrecambrianResearch-2011.pdf
DOI : 10.1016/j.precamres.2011.09.008

Éditeur(s) : HAL CCSD
Résumé : National audience
se sont accrétés au cours du Mésozoïque. Ainsi, la collisionentre les blocs Indochine et Chine du Sud a engendré l’orogénèseIndosinienne. Durant la première moitié du XXè siècle, cet orogènea été défini et documenté à partir d’une discordance, dite Indosinienne,mise en évidence dans le Nord du Vietnam. Les études alorsréalisées ont permis d’estimer un âge antérieur au Jurassique inférieurpour cette discordance, qui n’a depuis pas fait l’objet deréévaluation. Outre la discordance Indosinienne, de nombreux débatsportent sur l’âge de la collision, la vergence de la subductionocéanique qui l’a précédée ou encore l’existence d’un véritable domaineocéanique ayant séparé l’Indochine de la Chine du Sud.Les bassins permo-triasiques du Nord du Vietnam (bassins deSam Nua et de Song Da), situés de part et d’autre de la sutureophiolitique de Song Ma, constituent, via le flux sédimentaireprovenant de l’érosion et du volcanisme des zones adjacentes, desarchives essentielles pour documenter l’évolution tectonique ducouple Indochine-Chine du Sud. A partir de données sédimentologiques,géochronologiques (datation U-Pb sur zircons) et biostratigraphiques(foraminifères), nous proposons une réévaluationdu cadre stratigraphique du Nord du Vietnam. Ces données nouspermettent d’envisager un âge postérieur au Trias moyen pour ladiscordance Indosinienne. A l’aide de données géochimiques et del’analyse du remplissage sédimentaire et volcanique des bassins,il est possible de documenter un volcanisme d’arc, actif au Triasinférieur. La position de cet arc par rapport aux limites des blocsIndochine et Chine du Sud, marquée par la suture ophiolitique deSong Ma, implique (i) une zone de subduction qui plongeait vers leSud (coordonnées actuelles), sous le bloc Indochine, en marge (ii)d’un véritable domaine océanique, et non pas d’une croûte continentaleamincie, séparant les deux blocs jusqu’au Trias moyen.Nos interprétations, issues de l’analyse des bassins sédimentairespermo-triasiques du Nord Vietnam, permettent également de reconstituerl’évolution de l’orogénèse Indosinienne. Celle-ci faitsuite à la subduction de la croûte océanique rattachée à une plaqueChine du Sud sous une plaque Indochine au Trias inférieur (etprobablement au moins depuis le Permien inférieur). A partir dela fin du Trias moyen, les blocs Indochine et Chine du Sud entrenten collision et forment l’orogène Indosinienne.
RST 2016, livre des résumés
Caen, France

insu-01388676
https://hal-insu.archives-ouvertes.fr/insu-01388676

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Dahomey belt in Togo and Benin is an important segment of the larger West Gondwana Orogen. Here, we review the geodynamic evolution of the Dahomey belt and discuss new U–Pb and Lu–Hf zircon data in light of similar data previously acquired on the geologically related Northern Borborema Province, in NE Brazil. Eighteen samples from different tectonic settings and regions within the belt were collected for zircon isotopic investigation. Passive margin deposits of the Atacora Structural Unit and lower units of the Volta Basin have detrital zircon signatures compatible with the flanking West Africa Craton. The arc-related magmatism resulted from the east-dipping subduction of the Goiás-Pharusian oceanic lithosphere and is represented by a variety of granitoids emplaced in the Benino-Nigerian Shield between 670 and 610 Ma. These granitoids were mainly sourced from crustal reservoirs with subordinate juvenile input. Detrital zircon ages from syn-orogenic deposits in Benino-Nigerian Shield suggest that arc development could have started as early as 780 Ma. The main period of melting in the internal part of the belt, the Benino-Nigerian Shield, is related to crustal thickening and occurs only ca. 30 m.y. after initiation of the continental collision, marked by the ca. 610 Ma ultra-high pressure (UHP) metamorphism recorded at Lato Hills. Foreland development represented by the upper units of the Volta basin developed soon after continental collision and persisted with the development of the west-verging thrust front synchronously with the main period of crustal melting due to collision at ca. 580 Ma. The subvertical Transbrasiliano Lineament in South America, that corresponds to the Kandi Lineament in Africa, provides a present-day fit between NW Africa and NE Brazil. Restoration of the movement of the Transbrasiliano-Kandi Lineament (strike-slip plate boundary) places the Dahomey belt and Borborema Province (NE Brazil) along the same section of the West Gondwana Orogen. This configuration would explain some of the misfits previously discussed in the literature and aligns the UHP eclogites in Togo and NE Brazil.
ISSN: 0301-9268

hal-01358584
https://hal.archives-ouvertes.fr/hal-01358584
DOI : 10.1016/j.precamres.2016.01.032

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
A network of 26 GPS sites was implemented in Iran and Northern Oman to measure displacements in this part of the Arabia–Eurasia collision zone. We present the GPS velocity field obtained from three surveys performed in 1999 September, 2001 October and 2005 September and the deduced strain tensor. This study refines previous studies inferred from only the two first surveys. Improvements are significant in NE Iran. The present-day shortening rate across the mountain belts of NE Iran is estimated to 5 ± 1 mm yr−1 at about N11°, 2 ± 1 mm yr−1 of NS shortening across the eastern Kopet Dag and 3 ± 1 mm yr−1 of NS shortening across Binalud and Kuh-e-Sorkh. Our GPS measurements emphasize the varying character of the Kopet Dag deformation between its southeastern part with prevailing thrusting at low rates and its northwestern part with dominant strike-slip activity at increasing rates. The principal axes of the horizontal strain tensor appears very homogeneous from the Zagros to the Alborz and the Kopet-Dag (N20°) and in eastern Iran (Makran and Lut block: N30°). Only NW Iran suffers a variable strain pattern which seems to wrap the Caspian basin. The strain tensor map underlines the existence of large homogeneous tectonic provinces in terms of style and amplitude of the deformation.
ISSN: 0956-540X

insu-00346744
https://hal-insu.archives-ouvertes.fr/insu-00346744
DOI : 10.1111/j.1365-246X.2007.03477.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The East Sayan ranges are a key area to understand the interactions between the transpressive deformation linked to the far-field effects of the India-Asia collision and the extension linked to the opening of the Baikal Rift System. The active deformation that affects this range is very recent (around 5 Ma) but occurs in a very complex morphotectonic setting and the understanding of the Tertiary deformation relies entirely on a detailed knowledge of the pre-deformation situation. Using apatite fission track thermochronology, cosmogenic 10Be and morphological study on Tertiary lava flows we demonstrate that prior to the Oligocene the morphology of the East Sayan area was characterized by a wide, constantly rejuvenated erosion surface. Apatite fission track thermal modelling indicates that this surface started to form at least in Late Jurassic-Early Cretaceous (140-120 Ma). The long-term exhumation rates (several tens of million years) derived from apatite fission track data (17.5 m/Ma) and the short-term erosion rates (over a few hundred thousand years) derived from cosmogenic 10Be data (12-20 m/Ma) are coherent implying a near constant mean erosion rate since Late Jurassic. This constant, slow erosion prevented the formation of a lateritic-kaolinic weathering crust on the planation surface. By Oligocene-early Miocene times a long wavelength uplift that remains to be explained, induced incision that created shallow valleys later filled by basaltic lava flows. Finally, the present short-wavelength topography initiated during the Pliocene.
ISSN: 0743-9547

insu-00805603
https://hal-insu.archives-ouvertes.fr/insu-00805603
DOI : 10.1016/j.jseaes.2011.09.017

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

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

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Tapajós Domain in the Amazonian Craton comprises hundreds of gold occurrences mainly hosted by Paleoproterozoic granitic rocks, whose geotectonic evolution and deformation style are poorly understood. The Tocantinzinho granite hosts a large amount of gold, forming the largest gold deposit known in the Tapajós Domain. The Tocantinzinho area is formed by plutonic rocks cut by subvolcanic rocks shallowly emplaced and constrained by NW-SE strike-slip faults, probably in a transtensive site. The magmatism started with the emplacement of huge granodiorite that presently formed the basement country rocks (2007–1997Ma), it was followed by the Tocantinzinho granite magmatism (1989–1979 Ma), and the coeval to late andesite emplacement. Petrological and textural evidence suggest the complex and synchronous occurrence of tectonics and few magmatic events expressed by the emplacement of successive granite, aplite, pegmatite, andesite, and dacite. The magmatic event finished with the cooling of this set of rocks below c. 320 °C, at c. 1950 Ma. The cooling rates vary from c. 3.6–14.7°C/Ma, with an average of 7.5°C/Ma, indicating no important vertical exhumations. The elongated geometry of the Tocantinzinho granite and related rocks, features of solid-state deformation within granites and syntectonic deformation of some andesite dikes imply the existence of wrench type tectonic control. The I-type signature of these rocks, their high-K calc-alkaline and metaluminous to peraluminous affinities combined with the tectonic style indicate a post-collisional tectonic setting. Based on geochemical and structural constrains, the rocks from the Tocantinzinho area are interpreted as a part of the Creporizão Suite and probably represent the first expressions of this syn-to late-tectonic magmatism in the region. A continuous and progressive process of magmatic emplacement controlled by tectonics will be proposed and discussed in conclusion.
ISSN: 0895-9811

hal-01526936
https://hal.archives-ouvertes.fr/hal-01526936
DOI : 10.1016/j.jsames.2017.02.003

Éditeur(s) : HAL CCSD
Résumé : The mantle deformation processes that control the thinning and break-up of continental lithosphere remain poorly understood. Our knowledge is restricted to either lithospheric scale thermo-mechanical models --that use experimentally derived flow laws--, geophysical imaging and/or rare xenoliths from active continental rifts, such as the East African Rift System. The originality of this work relies on the study of the two largest outcrops of diamond facies subcontinental lithospheric mantle in the world: the Beni Bousera and Ronda peridotite massifs in N Morocco and S Spain, respectively. The structures and petrologic and metamorphic zoning preserved in these massifs --implying a polybaric and polythermal evolution-- provides a unique opportunity to investigate the thermo-mechanical evolution of thick subcontinental lithospheric mantle in extensional settings. In this thesis we studied the deformation mechanisms in both peridotites and pyroxenites to constrain the modes of exhumation of subcontinental lithospheric mantle from garnet-, to spinel-, and finally, to plagioclase lherzolite facies conditions. We combined field mapping of tectonometamorphic domains and structural mapping of ductile structures, microstructural analysis, crystal preferred orientations (CPO) measurements and conventional thermobarometric calculations and thermodynamic modeling (Perple_X) to unravel the pressure and temperature conditions of deformation. We showed that exhumation from garnet- to spinel lherzolite facies conditions was accommodated by fast shearing --in thermal disequilibrium--along a lithospheric scale transtensional shear zone. In this context, the petrological zoning and the large temperature gradient (ca. 100ºC/km) preserved in the Beni Bousera massif represent the mechanical juxtaposition of progressively deeper and hotter lithospheric levels at depths of ca. 60 km in the latest Oligocene (ca. 25 Ma). Final exhumation from spinel- to plagioclase facies lherzolite and emplacement into the crust is best recorded in the Ronda massif where it occurred by inversion and lithospheric scale folding of the highly attenuated continental lithosphere in a back-arc region, probably in relation with southward slab rollback and subsequent collision with the palaeo-Maghrebien passive margin in the early Miocene (21-23 Ma).
Les processus de déformation contrôlant l'amincissement de la lithosphère continentale sont encore mal contraints. Nos connaissances sont principalement basées sur la modélisation thermomécanique d'extension à l'échelle de la lithosphère--utilisant des lois rhéologiques derivées expérimentalement, l'imagerie géophysique et l'analyse de xénolithes provenant de rift continentaux actifs à ce jour, tels que le Rift Est-Africain. L'originalité de ce travail reside dans l'étude des deux plus grands massifs de péridotites sous-continentales ayant enregistrées des conditions primaires du facies à diamant: les massifs de Beni Bousera au nord du Maroc et de Ronda au sud de l'Espagne, respectivement. Les structures et la zonation petrologique et métamorphique --impliquant une évolution polybarique et polythermique-- préservéees dans ces massifs offrent une opportunité unique pour étudier l'évolution thermo-mécanique du manteau sous-continental dans un contexte extensif. Dans ce travail, nous avons étudié les mécanismes de déformation des péridotites et des pyroxénites afin de contraindre les modes d'exhumation du manteau lithosphérique sous-continental, depuis des conditions du facies des lherzolites à grenat, jusqu'au facies à spinelle et enfin à plagioclase. Nous avons combiné la cartographie des faciès tectono-métamorphiques et des structures ductiles de déformation, l'analyse des microstructures, la mesure d'orientations préférentielles de réseau (OPR), et la géothermobarométrie conventionelle couplée à la modélisation thermodynamique (PerpleX) afin de contraindre les conditions de pression et température de la déformation. Nous avons montré que l'exhumation précoce du facies à grenat au facies à spinelle était accomodée par une faille transtensive affectant le manteau lithosphérique. Dans ce contexte, la zonation tectono-métamorphique et le gradient thermique important (ca. 100ºC/km) préservés à Beni Bousera résultent de la juxtaposition mécanique de domaines lithosphériques initialement équilibrés à différentes pressions et températures, fossilisée à une profondeur de ca. 60 km durant l'Oligocène supérieur (ca. 25 Ma). L'exhumation finale du facies de lherzolite à spinelle au facies à plagioclase et l'emplacement final dans la croûte, mieux enregistrés dans Ronda, se sont produits par inversion et plissement de la section lithosphérique fortement amincie dans un contexte arrière-arc, probablement lors du retrait vers le sud de la lithosphère subduite et la collision de l'arc avec les paléo-marges maghrébines au Miocène inférieur (21-23 Ma).
https://tel.archives-ouvertes.fr/tel-00767700

tel-00767700
https://tel.archives-ouvertes.fr/tel-00767700
https://tel.archives-ouvertes.fr/tel-00767700/document
https://tel.archives-ouvertes.fr/tel-00767700/file/THESE_Frets.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Miocene (17-11 Ma) magmatic activity in the Kabylies emplaced K-rich (and minor medium-K) calc-alkaline plutonic and volcanic rocks in five zones, delineating a ∼450 km long EW trending strip located along the northern coast of Algeria, between Annaba and Algiers. Their most likely source is the Kabylian subcontinental lithospheric mantle previously metasomatized during the Paleogene subduction of the Tethys oceanic lithosphere. Our preferred tectono-magmatic model involves a Tethyan slab detachment combined with African mantle delamination and crustal stacking, leading to the superimposition of the African continental crust over the Kabylian metasomatized lithospheric mantle. At ca. 17 Ma, the asthenospheric upwelling arising from lithospheric delamination and Tethyan slab tear triggered the thermal erosion of the latter mantle, inducing its partial melting. The corresponding mafic medium-K calc-alkaline magmas interacted with the African basement units during their ascent, generating intermediate to felsic K-rich calc-alkaline melts that display a characteristic trace element and isotopic crustal signature. Later on, slab tears propagated eastward and westward, promoting slab rollback perpendicular to plate convergence and inducing the emplacement of magmatic rocks of decreasing ages from central-eastern Algeria towards Tunisia and Morocco.
ISSN: 0899-5362

hal-01467997
https://hal.archives-ouvertes.fr/hal-01467997
DOI : 10.1016/j.jafrearsci.2016.10.005

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The lateral variation of the mechanical properties of continental lithosphere is an important factor controlling the localization of deformation and thus the deformation history and geometry of intraplate mountain belts. A series of three-layer lithospheric-scale analog models, with a strong domain (SD) embedded at various depths, are presented to investigate the development of topography and deformation patterns by having lateral heterogeneities within a weak continental lithosphere. The experiments, performed at a constant velocity and under normal gravity, indicate that the presence or absence of the SD controls whether deformation is localized or distributed at a lithospheric scale. Deformation and topography localize above the edges of the SD, while the SD region itself is characterized by minor amounts of surficial deformation and topography. The depth of the SD (within the ductile crust, ductile mantle lithosphere, or both) controls the pattern of deformation and thus the topography. The presence of a SD in the ductile crust or in the mantle results in limited surficial topographic effects but large variations in the Moho topography. Strong Moho deflection occurs when the SD is in the ductile crust, while the Moho remains almost flat when the SD is in the mantle. When the SD occupies the ductile lithosphere, the SD is tilted. These analog experiments provide insights into intraplate strain localization and could in particular explain the topography around the Tarim Basin, a lithospheric-scale heterogeneity north of the India-Asia collision zone.
ISSN: 0278-7407

hal-01172472
https://hal.archives-ouvertes.fr/hal-01172472
DOI : 10.1002/2014TC003756

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
eoproterozoic eclogite and garnet amphibolites, representing retrogressed eclogites, from the Tassendjanet-Tidéridjaouine terrane in the Pan-African Western Hoggar (Tuareg shield, Southern Algeria) form lenses enclosed in 1.8 Ga subalkaline Paleoproterozoic orthogneisses. They lie along a major sinistral shear zone marking the boundary with the Archean/Paleoproterozoic granulitic In Ouzzal terrane and are associated with high-pressure metasediments. According to thermodynamic calculations, peak condition of the eclogitic stage is 650 °C, 20-22 kbar followed by post-peak heating and exhumation at 730 °C, 10-14 kbar and cooling to 610 °C, 7-10 kbar. Their major, trace-element and isotopic compositions are consistent with emplacement of former basalts in the shoulder of a 700-800 Ma continental rift that evolved to an oceanic basin. The eclogite and garnet amphibolites were thus part of the continental portion of a subducting slab that was pulled down by a denser oceanic lithosphere. Sheath and recumbent folds associated with the exhumation of HP units are verging toward the west, meaning that the former slab was dipping to the east. U-Pb zircon dating on metamorphic zircons bordering ilmenite and rutile in the eclogite gave an age of 623 ± 2 Ma, interpreted as the syn-collisional exhumation stage of the high-pressure unit. This event was rapidly followed by transpressional tectonics and abundant magmatism linked to the northward motion of the adjacent In Ouzzal terrane.
ISSN: 0301-9268

hal-01054338
https://hal.archives-ouvertes.fr/hal-01054338
DOI : 10.1016/j.precamres.2014.04.002