Provenance of Late Triassic sediments in central Lhasa terrane, Tibet and its implication

Abstract

In southern Tibet, Late Triassic sequences are especially important to understanding the assembly of the Lhasa terrane prior to Indo-Asian collision. We report new data relevant to the provenance of a Late Triassic clastic se- quence from the Mailonggang Formation in the central Lhasa terrane, Tibet. Petrographic studies and detrital heavy mineral assemblages indicate a proximal orogenic provenance, including volcanic, sedimentary and someultramafic and metamorphic rocks.In situdetritalzircon Hfand U–Pbisotopedata areconsistent with der- ivation of these rocks from nearby Triassicmagmatic rocks and basement that comprise part of the newly recog- nized Late Permian–Triassic Sumdo–Cuoqen orogenic belt. The new data suggests correlation with the Upper Triassic Langjiexue Group which lies on the opposing (southern) side of Indus–Yarlung ophiolite. Sediments from both the Mailonggang Formation and Langjiexue Group are interpreted to represent formerly contiguous parts of a sequence deposited on the southern flanks of the Sumdo–Cuoqen belt.