Mid--late Neoproterozoic tectonic evolution of the northern margin of the Yangtze Block, South China, as constrained from the detrital zircon record.

The northern margin of the Yangtze Block (NYB) experienced distinct tectonomagmatic evolution during the mid- and late-Neoproterozoic, as compared with the northwestern margins of the Yangtze Block (NWYB), although the geodynamic mechanism remains controversial. The South Qinling Belt (SQB), which forms the northernmost NYB, is a significant target for studying the Neoproterozoic tectonic evolution of the NYB. Here we present U-Pb geochronology and Lu-Hf isotopes of detrital zircons from clastic rocks belonging to the Yaolinghe and Wudangshan Groups in the SQB. The U-Pb ages reveal that the maximum depositional ages are respectively ca. 630 Ma and ca. 680 Ma for the Yaolinghe and Wudangshan Groups in the Ankang and Wudang Uplifts. Based on the compilation of U-Pb ages and Hf--Nd--O isotopic data as well as multidimensional scaling (MDS) analysis, clastic rocks of the Yaolinghe Group are suggested to be sourced mainly from the NWYB, whereas those of the Wudangshan Group were derived mostly from the NWYB and the NYB. The data compiled also indicate ca. 800-680 Ma northeastward migration of magmatism in response to slab rollback and ca. 680-600 Ma eastward migration of magmatism resulting from slab tearing. A tectonic model is proposed that envisages an arcuate subduction system around the Yangtze Block during the mid--late Neoproterozoic. The continuous slab rollback and slab tearing underneath the NYB resulted in an extensional environment at that time. The rocks in the NWYB underwent uplift and erosion, and the detritus was transported to the NYB. The new model can well account for the two distinct groups of volcanic rocks in the Yaolinghe Group. [ABSTRACT FROM AUTHOR]