Transition from forearc basin to syn-collisional basin in Southern Tibet (Paleocene Cuojiangding Group): Implication to timing of the India-Asia initial collision and of Yarlung Zangbo ophiolite emplacement

Abstract

In this study, we combine detailed stratigraphic, sedimentological and micropaleontological data on the Upper Cretaceous to Eocene succession of the Cuojiangding area, with sandstone petrography, detrital zircon U–Pb, and detrital Cr-spinel geochemistry data to reconstruct the paleotectonic evolution of the southern margin of Asia during the earliest stages of the India-Asia collision. Our data show that the Upper Cretaceous Padana and Qubeiya formations, deposited in deltaic to inner shelf environments, represent the final filling stage of the Xigaze forearc basin. The discomformably overlying Cuojiangding Group (Quxia and Jialazi formations), deposited in fan-delta environments during the Thanetian of Late Paleocene, represents the earliest syn-collisional stage. Petrographic data document progressive unroofing of the Gangdese arc, which was the main source of detritus during the Late Cretaceous to Paleogene. Detrital Cr-spinels in the Cuojiangding Group are geochemically similar to those of Xigaze forearc strata rather than to those of the Yarlung Zangbo ophiolites. The timing of the India-Asia initial collision should be older than the deposition of the Cuojiangding Group (>56 Ma), while the emplacement of the Yarlung Zangbo ophiolites is mostly post-middle Eocene