Tracing terrane origin through petrographic and geochronologic proxies: Insights from the Devonian deposits of the Bainaimiao arc terrane in the Central Asian Orogenic Belt
Shouxian Ma, Yingli Zhang, Dongsheng Wang, Zongqi Wang
Abstract
The Bainaimiao arc terrane (BAT) is a major subduction-accretionary system in the southeastern Central Asian Orogenic Belt, and its tectonic origin is a hotly debated topic. In this paper, we used petrography and zircon U-Pb-Hf isotopes to determine the provenance of the Chaganhebu Formation. We utilized the detrital zircon U-Pb ages of sandstone cobbles from Lower Chaganhebu to trace tectonic origin of the BAT. The presence of a south-directed paleocurrent, arc granitic cobbles during 457–430 Ma, and detrital zircon age populations of 1.6–0.4 Ga, indicate that the Chaganhebu Formation was sourced from the BAT. The cobble lithologies of conglomerates from the Lower Chaganhebu Formation indicate that the source rock assemblage comprises sedimentary rocks, granite, volcanic elements, and vein quartz. The Chaganhebu Formation exhibits a progradational sequence with matrix-supported conglomerates at its base, along with an upward increase in metasedimentary clasts and Precambrian recycled zircons. The above evidence indicates that the BAT experienced considerable uplift and exhumation in a retroarc foreland system. The sandstone cobbles from the Lower Chaganhebu are characterized by Grenville Orogen sources of 1.6–1.0 Ga age populations, and resemble the Upper Bayan Obo Group in the North China Craton. This similarity suggests that the BAT encompasses a Precambrian sedimentary basement in the Damaoqi region. Furthermore, the detrital zircon U-Pb ages of the sandstone cobbles, and the findings of previous studies on the crystalline basement and geomagnetic pole, demonstrate that the BAT represented a fragment that rifted from NW Laurentia during the breakup of the Rodinia supercontinent.