Supporting Information for [Timing of India-Asia suturing -evidence from remnant peripheral foreland basin in Xigaze, South Tibet]
The Yarlung-Zangpo Foreland Basin System records important information about the initial India-Asia continental collision. In the central-eastern Yarlung-Zangpo Suture Zone (YZSZ), the absence of robust foreland basin system has hindered understanding of the initial timing of India-Asia collision along strike. To address this issue, a remnant foredeep and wedge-top deposits of the foreland basin system are reported from the Tethyan Himalaya sequence and the YZSZ in Xigaze area. The foredeep is defined by the olistostrome of the Zongzhuo Formation, which consists of matrix and blocks including chert, limestone, sandstone and volcanic rocks. Based on the matrix, the Zongzhuo Formation is divided into two units. The lower member is the Zhilong unit composed of black shale and thin layers of siltstone in the matrix. The upper member, the Yongla unit, has distinct red shale or yellow-green siliceous mudstone in the matrix with interbedded siltstone and limestone. The Zongzhuo Formation is dated to 65 - 57 Ma by detrital zircon U-Pb chronology and radiolarian assemblages. In the YZSZ, the Puxia and Jiabi units are interpreted here as wedge-top deposit, consisting of mudstone matrix and exotic blocks such as sandstone, chert and limestone. Sandstone blocks from both units have maximum depositional ages (MDAs) of ca. 65 - 59 Ma. Detrital zircon provenance analysis and trace element data exclude an intra-oceanic arc and point to Gangdese arc and recycled accretionary wedge in the suture zone. Therefore, we proposed that the initial collision between India and Asia occurred at 65 Ma in the central-eastern YZSZ.