Detrital zircon U-Pb-Hf isotopes and whole-rock geochemistry of neoproterozoic-cambrian successions in the Cathaysia Block of South China: Implications on paleogeographic reconstruction in supercontinent

Abstract

Paleogeographic reconstruction of the Cathaysia Block of South China and its link with orogeny associated with Rodinia and Gondwana remain enigmatic, leading to controversial models proposed for supercontinental configuration. This study presents detailed provenance analysis of late Neoproterozoic to early Paleozoic sedimentary successions from the Cathaysia Block, to trace the sedimentary provenance, that was essentially linked to previously adjacent continents/blocks. Zircon U-Pb dating combined with published paleontological evidence suggests an Ediacaran depositional age range (633–542 Ma) for the Lechangxia Group, while deposition of the Bacun Group most likely commenced during early Cambrian. The older strata were sourced mainly from recycling of quartz rich sedimentary rocks while the younger one received sediments dominantly from felsic igneous rocks. High SiO2 contents (54.6–79.3 wt%) and K2O/Na2O ratios (0.69–35.7), detrital zircon age distribution and abundant monocrystalline quartz indicate a passive setting for Ediacaran and early Cambrian successions. In great contrast, the middle Cambrian strata was likely deposited in collisional setting, considering relatively lower SiO2 contents (67.9–74.5 wt%) and K2O/Na2O ratios (0.97–1.63) plus absence of old zircons. This tectonic transition is consistent with the change from quartz arenite to arkose that could be related to a disconformity between early and middle Cambrian strata.Dominant late Mesoproterozoic detritus (1250–1050 Ma) in the Lechangxia Group was possibly sourced from older Grenville orogens (1300–1050 Ma) in western Australia and East Antarctica because rocks of these ages are rare in the Cathaysia Block. Similarly, abundant early Neoproterozoic clastic (1000–950 Ma) in the late Ediacaran and early Cambrian successions imply an increasing input from younger Grenville orogens (990–950 Ma) in East Antarctica and eastern India. Thus the Cathaysia Block was a part of the East Gondwana assembly and was linked to eastern India, East Antarctica and western Australia during Ediacaran and Cambrian. The source change was coeval with the Pinjarra Orogeny (550–520 Ma) and the early stage of the Kuunga Orogeny (570–550 Ma). In middle Cambrian strata, the middle Neoproterozoic sediments (850–700 Ma) were mainly derived from intrinsic sources, likely to be the Wuyishan terrane. This provenance variation can be linked to the middle Cambrian uplift of the Cathaysia Block in synchronous with the later phase of the Kuunga Orogeny (530–480 Ma).