Abstract

Regional mapping of a north-south traverse from the India-Nepal-China border junction to Mount Kailas in southwest Tibet—combined with previously published geochronologic and stratigraphic data—is the basis for an incremental restoration of the Tethyan fold-thrust belt and deformation along the Indus-Yalu suture zone. From north to south, the major structural features are (1) the Indus-Yalu suture zone, composed of five south-dipping thrust faults involving rocks interpreted to represent parts of the former Indian passive margin and Asian active margin, (2) the Tethyan fold-thrust belt, composed of a dominantly north-dipping system of imbricate thrust faults involving Precambrian through Upper Cretaceous strata, and (3) the Kiogar-Jungbwa thrust sheet. A line-length cross-section reconstruction indicates a minimum of 176 km of north-south horizontal shortening partitioned by the Tethyan fold-thrust belt (112 km) and Indus-Yalu suture zone (64 km). Sequential restoration of the cross section shows that the locus of shortening prior to the late Oligocene occurred significantly south (possibly >60 km) of the Indus-Yalu suture zone within the Tethyan fold-thrust belt and that a significant amount of unsubducted oceanic lithosphere was present south of the suture in southwest Tibet until that time. An implication of this result is that postcollision (Oligocene/Miocene) high-K, calc- alkaline magmatism may be explained by melting due to active subduction of oceanic crust beneath the Kailas magmatic complex until the late Oligocene. A regional profile across the Tibetan-Himalayan orogen from the Subhimalaya to the Gangdese Shan (Transhimalaya), along with previously reported shortening estimates in the central Himalaya, yields a minimum shortening estimate across the orogen of ∼750 km.

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