Uplift-denudation history of the Qinling orogen: Constrained from the detrital-zircon U–Pb geochronology

Abstract

This paper presents a great number of detrital zircon U–Pb ages from the Middle Triassic to the Middle Jurassic sediments in the Jiyuan basin, southern North China. The results represent age spectra from 2.9Ga to 216Ma, with five peaks at 2.5Ga, 1.9Ga, 840Ma, 440Ma, and 270Ma and two grains of ∼220Ma. The ages of 2.5Ga and 1.9Ga are mainly derived from the Precambrian basement of the North China Block, whereas the others are typical characteristics of the Qinling orogenic belt. An important observation is that the Qinling-sourced detrital zircons become older as the strata get younger. Samples from the Middle Triassic to early Late Triassic strata are characterized by the age peak at 270Ma, whereas the Late Late Triassic to Early Middle Jurassic samples are dominated by age peaks at 840Ma and 440Ma and minor grains within 800–650Ma. Two grains of ∼220Ma are preserved in the Late Middle Jurassic sample, which may be contributed by the Carnian deep plutons. These signatures indicate that the unroofing pattern of the Qinling orogenic belt developed by the denudation of materials from young covers to old basements and the Carnian deep plutons. Integrated with the data reported from the Hefei Basin, it is well-established that the intensity of unroofing increased from the Qinling to the Dabie orogen in the Early Jurassic, and the denudation timing of the ultra-high pressure (UHP) and high pressure (HP) rocks or Carnian plutons changed successively from the Early Jurassic in the Dabie to the Late Middle Jurassic in the Qinling orogen.