Abstract
The highest elevation of the Tibetan Plateau, lying 5,700 m above sea level, occurs within the part of the Lhasa block immediately north of the India-Tibet suture zone (Yarlung Zangbo suture zone, YZSZ), being 700 m higher than the maximum elevation of more northern parts of the plateau. Various mechanisms have been proposed to explain this differentially higher topography and the rock uplift that led to it, invoking crustal compression or extension. Here we present the results of structural investigations along the length of the high elevation belt and suture zone, which rather indicate flexural bending of the southern margin of the Lhasa block (Gangdese magmatic belt) and occurrence of an adjacent foreland basin (Kailas Basin), both elements resulting from supra-crustal loading of the Lhasa block by the Zangbo Complex (Indian plate rocks) via the Great Counter Thrust. Hence we interpret the differential elevation of the southern margin of the plateau as due originally to uplift of a forebulge in a retro foreland setting modified by subsequent processes. Identification of this flexural deformation has implications for early evolution of the India-Tibet continental collision zone, implying an initial (Late Oligocene) symmetrical architecture that subsequently transitioned into the present asymmetrical wedge architecture.
Highlights
Our study region is located at the juxtaposition of continental crust forming southern Tibet (Lhasa block) and the Tethyan Himalaya along the YZSZ (Fig. 1)
We have inferred a retro foreland setting for the Zangbo suture zone, the Kailas Basin being the foredeep part of the setting
Accumulation in a contractional tectonic regime has been discounted[6] as (i) Kailas Formation onlap of Gangdese arc basement is not typical of facies generated from the hanging walls of bounding thrust belts, (ii) there is no evidence for contractional growth structures, (iii) the lithofacies pattern is not typical of wedge-top or proximal foredeep settings, and (iv), basaltic andesites and adakitic tuff in Kailas Formation suggests a thermal pulse possibly consistent with an extensional setting, perhaps associated with slab break-off
Summary
Our study region is located at the juxtaposition of continental crust forming southern Tibet (Lhasa block) and the Tethyan Himalaya along the YZSZ (Fig. 1). Between them lies (i) the Zangbo Complex, comprising elements of a Cretaceous subduction wedge (Xigaze flysch) with ophiolite that accreted to the leading edge of the overriding plate (Tibet) outboard of the Lhasa block during intra-oceanic subduction prior to the Tertiary start of continent-continent collision, and (ii), a much younger Oligocene) sedimentary succession (Kailas Basin) that onlaps the Gangdese belt and is separated from the Zangbo Complex by the GCT (Fig. 2A-A”)
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