Abstract

This study concerns the mélange that crops out in the north of Saiqu, Sagya County, southern Tibet. The age of the mélange has been debated for years, because the ages of fossils from various blocks conflicted with each other, and no macrofossils had been discovered from the matrix. Furthermore, no one had looked at the matrix for microfossils, mainly because of their mistaking this suite of mélange as straightforward sedimentary strata. However, abundant microfossils are present in the matrix of the mélange, and four radiolarian assemblages have been recognized: (1) Holocryptocanium aff. barbui-Dictyomitra turris; (2) Acanthocircus dicrancanthos-Thanarla pulchra; (3) Thanarla veneta-Pseudodictyomitra pseudomacrocephala; and (4) Dictyomitra magnifica-Dictyomitra turritum. The matrix-derived radiolarian assemblages indicate a Late Cretaceous age. The mélange in Saiqu can be correlated with the Zongzhuo Formation of neighbouring regions by either lithological associations or fossil assemblages. Consequently, the mélange has been referred to the Upper Cretaceous Zongzhuo Formation, instead of the Triassic Xiukang Group, with which it was previously associated. The mélange of the Zongzhuo Formation resulted from the subduction of the Indian Plate beneath the Asian Plate during the Late Cretaceous