Miocene post-collisional shoshonites and their crustal xenoliths, Yarlung Zangbo Suture Zone southern Tibet: Geodynamic implications

Hébert, Réjean R.; Guilmette, Carl C.; Dostál, Jaroslav V. J.V.; Bezard, Rachel R.; Lesage, Guillaume G.; Bédard, Émilie E.; Wang, Chengshan C.

Abstract

The convergence in between the Indian plate and the southern margin of the Eurasian continent created at active continental margin from Late Jurassic until about 40 Ma ago, Which then evolved to form the Himalaya and the Tibetan Plateau falling on the continental collision stage. Post-collisional magmatism in southern Tibet, Yarlung Zangbo Suture north of the zone (YZSZ) HAS BEEN active since 45 Ma and is related to normal faulting and extensional tectonism. To date no such thing magmatism reported within the YZSZ Itself. This paper reports on the discovery of Miocene shoshonites within the YZSZ. They are significant: because the magma traveled, at least in part, through oceanic crust, ran thus limiting interaction with the continental crust to the mid-crustal level and Which affected the post-collisional magmatic rocks Occurring in the northern part of the subduction system. In addition, xenoliths and xenocrysts of crustal origin in synthesis rocks constrain the nature of metamorphic rocks underlying the YZSZ at mid-crustal level. The geochemical signatures of the shoshonitic rocks, Nd and Sr isotope systematics Including, indicate indicating derivation from a garnet-bearing middle continental crustal source. Crustal imprint complicates modeling of the petrochemical genetic Processes Which occurred prior to mid-crustal ponding of the magma Which Took place in between 11 and 17 Ma at depths of 40 to 50 km. The significant role of crustal contamination raises serious Concerns about Proposed models for similar magmatic activity elsewhere in the Himalaya and the Tibetan Plateau. © 2013 International Association for Gondwana Research.