Subduction-collision and rapid uplift of the NW Yangtze Block during the Ediacaran-Cambrian transition: new evidence from the shoshonite series

The NW Yangtze Block has long been regarded as a passive continental margin during Ediacaran and Cambrian. However, with the deepening of the regional geological survey and deep oil and gas exploration, the depositional sequence and palaeogeographic patterns of Ediacaran and Cambrian in the Sichuan basin are not consistent with the general sedimentary evolution process of passive margin more and more. To fully understand the tectonic property and palaeogeography of the NW Yangtze Block, a comprehensive study of the whole rock geochemistry, zircon U-Pb chronology and Hf isotopic composition analysis were carried out on the Weimen volcanic rocks, which mainly consist of trachyte, trachy-andesite, andesite, dacite, and rhyodacite in Maoxian area. They have high light rare earth element (LREE) and large ion lithophile element (LILE) concentrations, but are depleted in high field strength elements (HFSE). They are characterized by having high K₂O+Na₂O (5.60–9.48%), MgO (1.47–4.58%), Ce/Yb (11.67–25.79), and normalized hypersthene (Hy = 2.14–14.17), indicate an unambiguous feature of the shoshonite series. LA-ICP-MS zircon U-Pb dating results show that the volcanic rocks have crystallization ages ranging from 528 Ma to 523 Ma, with positive zircon ε_Hf (t) ranging from + 1.31 to + 5.26. In combination with previous studies, the early Cambrian shoshonite series in Maoxian area are interpreted to be formed in a continental collision setting. Therefore, the discovery of the shoshonite series suggests that the NW Yangtze Block has experienced an important process of continental subduction and collisional orogeny in response to the Gondwana assembly, and consequently provided a large amount of terrigenous sources to rapidly fill into the early Cambrian foreland basin. Firstly report 530-520 Ma shoshonite series in NW Yangtze.Weimen shoshonite series demystify the dynamics of the cratonic rift.NW Yangtze underwent continental collision and rapid uplift from Ediacaran to Cambrian. Firstly report 530-520 Ma shoshonite series in NW Yangtze. Weimen shoshonite series demystify the dynamics of the cratonic rift. NW Yangtze underwent continental collision and rapid uplift from Ediacaran to Cambrian.