Apatite fission-track thermochronological constraints on the pattern of late Mesozoic–Cenozoic uplift and exhumation of the Qinling Orogen, central China

Abstract

The Qinling Orogen of central China was formed by intracontinental collision between the North and South China Blocks. The orogen comprises several micro-blocks bounded by sutures and faults, and has undergone long-term intracontinental deformation since the Late Triassic. The micro-blocks include the southern margin of the North China Block (S-NCB), the Northern Qinling Belt (NQB), the Southern Qinling Belt (SQB), and the northern margin of the South China Block (N-SCB). Under a uniform tectonic setting in late Mesozoic–Cenozoic, these micro-blocks have been subjected to a range of deformation styles, as demonstrated by their structural deformation, history of magmatism, and the development of sedimentary basins. To investigate the differences among the micro-blocks and to quantify their uplift and exhumation, we obtained 45 rock samples from eight Mesozoic granites in these micro-blocks, and conducted apatite fission-track (AFT) thermochronological modeling. The results reveal that the Qinling Orogen underwent four distinct stages of rapid cooling histories during the late Mesozoic–Cenozoic, and showed variation in uplift and exhumation whereby the intracontinental deformation started in the south (the N-SCB) and propagated to the north (S-NCB). In the first stage, during the Late Jurassic–Early Cretaceous (ca. 160–120Ma), rock cooling occurred mainly in the N-SCB, attributed to the clockwise rotation and northward subduction of the South China Block beneath the Qinling Orogen. In the second stage, compression- and extension-related uplift was initiated during the late Early Cretaceous–early Late Cretaceous (ca. 120–90Ma) in the SQB, consistent with the southward subduction of the North China Block and broadly extensional deformation in the eastern China continent. In the third stage, a gentle regional-scale cooling event that occurred during the latest Cretaceous–Paleocene (ca. 90–50Ma) started in the NQB and became widespread in the Qinling Orogen. This regional-scale uplift and exhumation event was probably a response to the opposite polarity subduction beneath the Qinling Orogen combined with the effects of subduction of the Pacific Plate from the southeast. The fourth stage (Eocene–Oligocene, ca. 50–20Ma) was marked by another phase of rapid cooling in the S-NCB, the NQB, and the NW-SQB, and is interpreted as being cause by the eastward tectonic escape of Tibetan Plateau related to India–Asia collision. Furthermore, the record of variable timings and rates of cooling of these micro-blocks, together with regional structural analysis, indicates that the late Mesozoic–Cenozoic intracontinental deformation in the Qinling Orogen was characterized by a spatiotemporally variable and propagating-style uplift and exhumation of the micro-blocks, and the predominant deformation was through displacement across various boundary sutures and faults.