The `Gangdese thrust' was not Responsible for Uplift of Southern Tibet
Abstract
It has been proposed that a major south-directed structure was the mechanism for Late Oligocene to Miocene uplift of the Tibetan Plateau [Yin et al., 1994]. This feature, referred to as the `Gangdese thrust', is reportedly located along the southern edge of the Lhasa terrane marginal to the Yarlung Tsangpo suture zone. Acceptance of the `Gangdese thrust' hypothesis has become an integral component of models for the development of the Tibetan Plateau. Based on our own extensive field mapping along the Yarlung Tsangpo suture zone we question the existence of this particular south-directed thrust fault anywhere in southern Tibet. We have walked numerous sections where the trace of this structure is mapped. At localities around, and east of Zedong, we were unable to observe any south-directed thrust fault. Instead we report a depositional contact between felsic intrusives of the Gangdese batholith and foliated metamorphic rocks in the southern Lhasa terrane and the overlying Lower Miocene Luobusa conglomerates. This nonconformity is mappable for 200 km from Zedong to Long Xian. Conglomerates inferred to lie in the footwall of the proposed thrust were previously assigned a Tertiary age in error. These rocks are part of the Lhasa terrane and belong to the Late Jurassic - Early Cretaceous Bima Formation within the Sangri Group. It has also been suggested that the contact between turbidites of the Xigaze terrane and ophiolitic rocks to their south is another south-directed Gangdese-style thrust. Mapping around Xigaze and, as far west as, Lhaze indicates that, once again, this is not the case. This fault is typically a high angle, north-directed, reverse fault with ophiolitic rocks in the hanging wall. The rapid uplift of the Tibetan Plateau had a profound effect on the evolution of global climatic systems. If the `Gangdese thrust' does not exist then interpretations that invoke uplift along this structure as an explanation may be seriously flawed. Reference: Yin, A., T.M. Harrison, F.J. Ryerson, W.J. Chen, W.S.F. Kidd, and P. Copeland, Tertiary structural evolution of the Gangdese thrust system in southeastern Tibet, Journal of Geophysical Research, 99, 18175-18201, 1994.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.T12F..08A
- Keywords:
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- 8102 Continental contractional orogenic belts