Exhumation history of the Jiaodong and its adjacent areas since the Late Cretaceous: Constraints from low temperature thermochronology

Abstract

The thermal history of the Jiaodong region and adjacent provinces (Shandong and northern Jiangsu) have been extensively studied, particularly by apatite fission track (AFT) dating. However, the AFT ages from surface outcrops range broadly and do not show an apparent relationship between age and elevation. This work provides a multiple low temperature thermochronological dataset including zircon and apatite (U-Th)/He ages (ZHe and AHe), and AFT ages from a 1000-m-deep borehole at the Jiaojia goldfield in the northwest of Jiaodong Peninsula. ZHe, AFT and AHe ages range from ~100–70, ~85–50 and ~65–50 Ma, respectively. These data conform to the principles of age vs. closure temperature and age vs. elevation and thus can be employed to estimate the exhumation history. Based on the density histogram of fission track length calculation, thermal history modeling, and previously published AFT ages from the Chinese Continental Science Drill program, this work concludes that compared to the AFT ages from surface outcrops, the low temperature thermochronological ages from the boreholes show a better relationship between age, elevation and closure temperature, and the age becomes younger with increasing depth. In addition, the exhumation history in the Jiaodong and adjacent areas can be divided into two distinct stages: a short, rapid tectonic exhumation (~100–95 Ma) and a long, slow exhumation since 95 Ma. The rate and amount of tectonic exhumation since 95 Ma are inferred as ~30 m Ma - 1 and ~3 km, respectively.