History of subduction erosion and accretion recorded in the Yarlung Suture Zone, southern Tibet

The history of pre-Cretaceous subduction accretion and erosion along the Yarlung Suture Zone remains poorly constrained. We present new geological mapping along c. 200 km of the suture zone, 4881 detrital zirconU—Pb ages, and sandstone petrography for the subduction complex and Tethyan Himalayan strata. We provide the first documentation of the c. 158 Ma marine Xiazha Formation, which contains volcanic clasts of intermediate to felsic volcanic rocks and ooids with both calcareous and volcanic cores. Based on our new data and synthesis of published data, we present a model in which the Zedong arc represents the southwards migration of the Gangdese arc onto a forearc ophiolite that was generated proximal to the southern Asian margin during Neotethyan slab rollback at 160—150 Ma. This contrasts with previous suggestions that the Zedong arc, Yarlung ophiolites and subduction complex rocks developed above an intra-oceanic subduction zone thousands of kilometres south of Asia. Although Gangdese arc magmatism began in the Middle Triassic, the only forearc units preserved are 160 Ma until collision between the Xigaze forearc basin and Tethyan Himalaya at c. 59 Ma. This suggests that almost all pre-Cretaceous forearc assemblages have been removed by subduction erosion at the trench.