Abstract
The ongoing Cenozoic Indo-Asia continental collision not only formed the highly elevated Tibetan Plateau but also reactivated the crustal deformation in adjacent Paleozoic-Mesozoic orogens. This includes the renewed phase of deformation in the Qinling Orogen, northeast of the Tibetan Plateau, which was formed initially by Paleozoic closure of the Paleo-Tethys and subsequent early Triassic continental collision between the North and South China blocks. Debates continue as to when and how the reactivation initiated. To investigate this question, this study reports a vertical profile of apatite and zircon (U???Th)/He thermochronometric ages from the Guangtoushan Granite to estimate the exhumation history of the central Qinling Orogen, where previous models for the growth of the Tibetan Plateau inferred late Cenozoic northeastward growth of the Tibetan Plateau by outward flow of the lower crust from the plateau interior. Age-elevation relationship and thermal history modelling suggest two phases of relatively rapid exhumation during the early Cretaceous (-130???110 Ma) and the latest Cretaceous ??? early Paleocene (-70???50 Ma), respectively. The early Cretaceous exhumation coincided with the time of the Lhasa-Qiangtang collision, whose far field effects have been widely reported in regions of the central-northern Tibetan Plateau. In the southern and central Qinling, our finding of an early Paleocene (-70???50 Ma) increase in exhumation rate followed by minimal exhumation during the late Cenozoic suggests negligible impact of the lower crust flow from the expanding Tibetan Plateau on the rock exhumation of the Qinling. Instead, our study suggests instant strain migrations from the Lhasa-Qiangtang and Indo-Asia collision zones to the northeast margin of the Tibetan Plateau during the early Cretaceous and the early Paleocene, respectively, supporting the models highlighting the importance of rigid blocks in facilitating intracontinental strain migration.
NSTL
Elsevier