Revisiting Phanerozoic evolution of the Qinling Orogen (East Tethys) with perspectives of detrital zircon

Abstract

This paper presents 5383 detrital zircon U–Pb and 2079 Lu–Hf isotopic data, shedding new light on the Phanerozoic tectonic evolution of the Qinling Orogen. The Silurian rocks are characterized by negative εHf(t) values of early Paleozoic and Neoproterozoic zircon, which in the Devonian to Carboniferous samples show both positive and negative εHf(t) values. Late Paleozoic zircon peak with negative εHf(t) values occurs in the upper Carboniferous to Cretaceous strata. The Permian to Cretaceous strata show peaks at 1.9 Ga and 2.5 Ga. Early Paleozoic and Neoproterozoic peaks are back in Upper Triassic to Cretaceous rocks. A Mesozoic peak with negative εHf(t) values occurs in Cretaceous rocks. In terms of the sources of detrital zircon, the South Qinling Belt and Yangtze Block are major contributors for Silurian strata; South Qinling and North Qinling belts are major sources for Lower Devonian to upper Carboniferous rocks; early Carboniferous detrital zircon related to subduction of Mianlue oceanic slab emerges in upper Carboniferous rocks; North China Block is an important source for Lower Permian to Upper Triassic rocks; Lower Cretaceous strata exhibit diverse provenance, including North Qinling Belt, North China Block, and South Qinling Belt. Provenance changes suggest that the initial spreading of the Mianlue Ocean occurred in the Early Silurian during which the South Qinling Terrane and Yangtze Block had not completely separated. The Mianlue Ocean evolved into a mature stage of spreading in the Early Devonian. Meanwhile, the closure of the Shangdan Ocean took place. The Mianlue Ocean started to subduct in the early Carboniferous. Its final closure occurred in the Late Triassic, leading to uplift and exhumation of Qinling Orogen and cutting off detritus transport from North China Block in the Jurassic. The Qinling Orogen underwent collapse in the late Early Cretaceous.