The Pre-Mesozoic crustal evolution of the Cathaysia Block, South China: Insights from geological investigation, zircon U-Pb geochronology, Hf isotope and REE geochemistry from the Wugongshan complex

Abstract

The multiphase emplacements of granitoids and well-developed depositional sequences from Neoproterozoic to Mesozoic are exposed widely in the Wugongshan domain of South China provide important keys for the reconstruction of the pre-Mesozoic tectonic evolution of the Cathaysia Block. Here we present the results from geological investigations, detrital zircon U-Pb geochronology, in situ Hf-isotope and REE composition of the Ordovician meta-sandstones, together with the U-Pb age data on a Mesozoic pluton with an attempt to evaluate the petrogenesis and crustal evolution history. A group of 276 detrital zircon U-Pb ages are reported from four meta-sandstones which show five major age populations: 2630-2350 Ma with a peak of 2440 Ma, 1890-1540 Ma (peak of 1680 Ma), 1120-870 Ma (peak of 980 Ma), 810-700 Ma (peak of 760 Ma) and 660-510 Ma (peak of 550 Ma). Among these, the most prominent age at 980 Ma fits well with the collisional event of Yangtze and Cathaysia Blocks. The second prominent age at 760 Ma correlates with a breakup of Rodinia, and the third one at 1680 Ma corresponds to the initial breakup of Columbia. For the fourth (peak of 2440 Ma) and fifth (peak of 550 Ma) ages, no corresponding magmatic rocks are exposed in the study area or in the adjacent regions, although the age populations broadly correspond to the global continental growth in the early Paleoproterozoic and the latest Neoproterozoic 'Pan-African' orogeny. We obtained 132 in situ Hf isotope compositions, among which 98 show negative εHf(t) values (-36.88 to -0.3) with two-stage model ages (TDM2) of 3.5-1.7 Ga (peak of 2.2 Ga), and 34 display positive εHf(t) values (+0.3 to +9.89) with crystallization ages of 1.5-1.1Ga (peak of 1.4 Ga).Zircons from two Mesozoic granitic samples yield rather similar late Jurassic ages of 158.1 ±. 2.1 Ma and 154.0. ±. 3.9 Ma. All the corresponding εHf(t) values of zircons are negative (-. 24.2 to -. 4.2) and the Hf two-stage model ages range from 1.5 to 3.0 Ga with a peak of 1.68 Ga. Combined with previous age data on 120 Ma massive granitoids and 230 Ma on ductile sheared plutons, we consider that the magmatism in the Wugong complex started from the late Triassic, and reached a peak in the late Jurassic, but was gradually weakened since the early Cretaceous (130 Ma) and culminated at 120 Ma. Almost all the Wugongshan granitic plutons were derived from the partial melting of Mesoproterozoic crustal material, with little mantle components. We also discuss the provenance of the metasedimentary rocks and pre-Mesozoic crustal evolution of Cathaysia.