Early Neoproterozoic tectonic evolution of northern Yangtze Block: Insights from sedimentary sequences from the Dahongshan area

Abstract

Precambrian sedimentary strata are widely distributed along the periphery of the Yangtze Block. However, the age, provenance and tectonic setting of the sedimentary successions on the northern margin still remain unclear, which exerted considerable influence on the understanding of Precambrian crustal evolution of the Yangtze Block. Here we report integrated detrital zircon U-Pb dates and Lu-Hf isotopes from the Dahongshan area to the northeast of the nuclei (i.e. the Kongling Complex) of the Yangtze Block. The youngest U-Pb dates of 995 Ma and 810 Ma of detrital zircon grains place constraints on the maximum depositional ages of the underlying Dagushi Group and the overlying Huashan Group, respectively. Both groups show pre-Mesoproterozoic age populations at ca. 2050 Ma and ca. 2700 Ma and corresponding εHf(t) values varying from –24.1 to + 2.3, consistent with counterparts of the Kongling Complex and Yangpo Complex in northern Yangtze Block. The εHf(t) values of Neoproterozoic (1000–800 Ma) detrital zircon grains in the Huashan Group show a decrease after ca. 880 Ma (from + 13.5 to –18.5), possibly indicating a transition from arc-continent collision to continental arc setting on the northern margin of the Yangtze Block. In combination with sedimentary characteristics and the new isotopic results, the Dagushi Group probably formed in a shallow marine basin setting and received dominant detritus from the Kongling and Yangpo complexes. In contrast, the Huashan Group received sediments recycled from the underlying Dagushi Group and contemporary igneous rocks in the Dahongshan and Kongling areas. The changes in provenance and tectonic setting recorded in the two sedimentary sequences suggest a tectonic transition from late Mesoproterozoic passive continental margin to Neoproterozoic subduction and accretion in response to the amalgamation of Rodinia supercontinent. On the basis of distinct location and history, Pre-Nanhua Neoproterozoic sedimentary sequences distributed in the periphery of Yangtze Block are dispersed into four separate domains. Through bivariate kernel density estimates and bootstrap resampling method, we have identified that these domains were characterized by asynchronous igneous impulse and heterogeneous character of igneous activity in early Neoproterozoic along with varying degrees of integration of crustal growth and reworking.