Tectonic affinity of the Khanka Massif in the easternmost Central Asian Orogenic Belt: evidence from detrital zircon geochronology of Permian sedimentary rocks

摘要

The tectonic affiliation of the Khanka Massif, in the easternmost section of the Central Asian Orogenic Belt (CAOB), is still a matter of debate. Here, we provide new constraints on the provenance and timing of deposition of Permian strata in the western margin of the Khanka Massif. The results, which include U-Pb dating of detrital zircon grains using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), provide evidence regarding the tectonic position of the Khanka Massif and its role in the late Palaeozoic evolution of the eastern CAOB. Detrital zircon grains from a sublitharenite (Pingyangzhen Formation), a litharenite (Liangzichuan Formation), and a metamorphic siltstone (Qinglongcun Group) yielded multiple age populations ranging from Neoproterozoic (~914 Ma) to Permian (~272 Ma). Combined with age constraints from overlying/late-stage igneous rocks and other magmatism of the Khanka Massif, we conclude that the dated strata were deposited during the early-middle Permian and were sourced from the Khanka Massif. A comparison between the detrital zircon age populations and the history of magmatic activity in the neighbouring areas suggests that the Khanka Massif was tectonically linked to the Songnen-Zhangguangcai Range Massif. Based on tectonic discrimination diagrams, we conclude that the western margin of the Khanka Massif was positioned in a convergent-boundary basin during the early-middle Permian. Strike-slip faulting along the Dunhua-Mishan Fault, in response to ridge subduction of the Paleo-Asian Ocean Plate, resulted in a north-eastward movement of the Khanka Massif. The occurrence of Precambrian detrital zircon grains (with ages of 1900-1700 and 900-700 Ma) implies the presence of an ancient basement within the Khanka Massif.