Late Silurian to Late Triassic seamount/oceanic plateau series accretion in Jinshajiang subduction mélange, Central Tibet, SW China

Abstract

The timing of the initial opening and subduction of the Palaeotethyan Ocean is currently highly debated, in particular regarding the Jinshajiang Ocean in the central Tibetan Plateau. This study presents four well‐constrained U–Pb zircon ages (422.4 ± 6.1, 336.4 ± 7.4, 272.3 ± 2.8, and 255.8 ± 3.4 Ma) of mafic blocks in the Jinshajiang Suture. These mafic blocks have a chemical oceanic island basalt (OIB) affinity. These facts, together with previously published data (236 Ma OIBs), may be interpreted as a series of seamounts/oceanic plateaux varying from Late Silurian to Late Triassic, which were accreted early in the subduction–accretion process. An andesite from the Jinshajiang Suture with continental arc characteristics yielded a zircon U–Pb weighted average age of 385.2 ± 6.6 Ma, implying that the subduction initiation may have occurred at least in the Middle Devonian. Our work suggests a long‐lived continuous accretion, which also puts an earlier initial opening time than previously thought. Taking into account the above data and integrated with relevant published information, we favour a long‐lived accretionary process accompanied with seamounts/oceanic plateaux, which provides robust new evidence for subduction‐related continental growth in the central Tibetan Plateau.