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De la convergence intra-océanique à l'évolution post-collisionnelle : exemple de la convergence indo-asiatique en Himalaya du NW du Crétacé à nos jours

Abstract : The NW himalayan segment (Kohistan-Ladakh Arc and Karakoram, NE Pakistan and NW India) is a suitable zone to study the stages of the convergence of two continents (lndia and Asia), in an intra-oceanic and in an intra-continental context, during 110 Ma. A multi-disciplinary approach (structural geology, petro-geochemistry, thermobarometry, and Ar-Ar geochronology) has been used. The intra-oceanic stages of the convergence have been studied in the preserved tethyan arc series of Kohistan-Ladakh. This study outlines the continuity from Kohistan intra-oceanic arc in the W to the Tibetan andean margin in the E. An isotopic study (Sr, Nd and Pb) of the arc lavas yields elevated isotopic ratios similar to those defining the "DUPAL" anomaly. Adakitic and Nb, Ta, Ti rich lavas are also present. These data suggest interactions between crustal melts and mantle, fo llowing the subduction of the mid-oceanic ridge, similarly to the Oman ophiolite, which could be due associated to the tectonic inversion due to northward drift of India. The post-collisional stages, after a phase of crustal thickening in a NE-SW shortening context between 60 and 40 Ma are characterised by a tectonic partition: An E-W band of domes crosscuts the former structures, in a N-S shortening and vertical extrusion context linked to HT metamorphism, in the granulite facies and to magmatism with mantellic affinities (25 - 5 Ma). This granulitisation could be Iinked to advective heat input from the asthenosphere, due ta detachment of the Indian sIab. The Karakoram strike-slip fault accommodates the lateral extrusion of Tibet. Granulites exhumed in the fault zone suggest that it could be a Iithospheric scale fault. Dextral slip of the fault appears to be heterogeneous, with a total offset deduced from Lhasa and Karakoram blocs correlation, of approximately 300 km.
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Submitted on : Thursday, May 24, 2012 - 3:21:55 PM
Last modification on : Friday, March 25, 2022 - 11:08:44 AM
Long-term archiving on: : Thursday, December 15, 2016 - 9:54:08 AM

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Yan Rolland. De la convergence intra-océanique à l'évolution post-collisionnelle : exemple de la convergence indo-asiatique en Himalaya du NW du Crétacé à nos jours. Tectonique. Université Joseph-Fourier - Grenoble I, 2000. Français. ⟨NNT : ⟩. ⟨tel-00701083⟩

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