Early Cretaceous rapid exhumation processes in the southern Great Xing’an Range, NE China: implications for extensional geodynamics

Abstract

ABSTRACT The Mesozoic-Cenozoic geological evolution of the southern Great Xing’an Range (GXR) has long been controversial since it is located in the superposed region of different tectonic regimes and involves complex interactions. Here, we present low-temperature thermochronological data from granitoids emplaced in multiple magmatic stages to delineate the tectono-thermal history and further understand the geodynamic process. Most zircon and apatite (U-Th)/He ages, within error, indicate Early Cretaceous: the zircon average (U-Th)/He ages range from 146.7 ± 8.7 to 120.0 ± 7.1 Ma, except for the oldest data (162.5 ± 9.6 Ma) and the apatite (U-Th)/He ages vary from 138.7 ± 8.2 to 94.8 ± 7.5 Ma, except for the youngest age (70.8 ± 4.3 Ma). Systematic numerical modelling reveals that a rapid cooling and exhumation process with rates of 2.5-10 oC/Ma and 0.07-0.29 mm/yr occurred in the southern GXR during the early Cretaceous (145–110 Ma). We propose that the rapid uplift and exhumation of intrusive rocks during the early Cretaceous is also a manifestation of the extensional regime in the southern GXR, which is dominated by the rollback of the subducted Paleo-Pacific oceanic plate superposed by the post-orogenic extensional collapse of the Mongol-Okhotsk belt. In addition, the slow exhumation process since the late Cretaceous (~0.01 mm/yr) suggests that the Paleo-Pacific Ocean tectonic regime has a weak impact on the southern GXR area.