Provenance analysis of upper Cretaceous strata in the Tethys Himalaya, southern Tibet: Implications for timing of India-Asia collision

The provenance of upper Cretaceous strata in the Tethys Himalaya provides critical constraints on the closure time of the Neo-Tethys Ocean and the initial India-Asia collision. This paper reports detailed petrographic studies, in-situ detrital zircon U-Pb ages and Lu-Hf isotopic analyses, whole rock Nd-isotopes, and Cr-spinel electronic microprobe data from upper Cretaceous clastic sedimentary rocks of the Tethys Himalaya near Gyangze, southern Tibet. The Berriasian-Coniacian Jiabula Formation consists of black mudstone, chert and minor quartz arenite, and is dominated by detrital zircons with Archean-Cambrian U-Pb ages which were most likely derived from the Indian continent. Overlying conformably is the Santonian-Maastrichtian Chuangde Formation, which consists of red shale, limestone and chert. The Chuangde Formation is in turn overlain by the late Maastrichtian-late Paleocene Zongzhuo Formation, which is composed of black mudstone and lithic sandstone enclosing various olistoliths of sandstone, limestone and chert. The Rilang conglomerate is a lens which is located within the upper part of the Zongzhuo Formation and consists of an upward-thinning and fining succession of volcanic conglomerate, sandstone and black mudstone. The Zongzhuo Formation and the Rilang conglomerate record an abrupt influx of Cretaceous zircon grains with juvenile Hf isotopic compositions, arc-related Cr-spinels and positive epsilon Nd-(0) sediments, suggesting an arc and suture-zone provenance. The change in provenance of upper Cretaceous strata from the southern Indian continent to a northern arc and suture zone is attributed to either (1) initial collision between the Indian plate and Lhasa terrane, or (2) initial collision between the Indian plate and an intra-oceanic arc. We prefer option (1) that the initiation of India-Asia collision occurred during Maastrichtian (similar to 70-65 Ma). (C) 2011 Elsevier B.V. All rights reserved.