Stratigraphy, Geochronology and Tectonic Signification of the Permian Volcanicsedimentary Rock Series in Airgin Sum Area, Inner Mongolia

WANG Shichao1, XU Bei1,2,†, WANG Zhiwei2, ZHANG Jiaming1, LI Jin1

1. Key Laboratory of Orogenic Belts and Crustal Evolution (MOE), School of Earth and Space Sciences, Peking University, Beijing 100871; 2. Laboratory of Region Tectonics and Mineralization, Hebei GEO University, Shijiazhuang 050031; † Corresponding author, E-mail: bxu@pku.edu.cn

Abstract Several rift basins developed in the western part of Xing’an-mongol orogenic belt during late Paleozoic, in which volcanic-sedimentary series is important to understand the late Paleozoic tectonic evolution, however, there is not a clear space-time distribution of the series. Stratigraphy and geochronology of Xilimiao Formation have been researched to understand the basin filling process and tectonic setting. According to the field sections, Xilimiao Formation can be divided into three segments. Upper and lower segments are composed of crystal tuffs and rhyolitic lithic crystal tuffs, and middle segment are dark sedimentary rocks. The zircon 206PB/238U age of 282±2 Ma achieved from the rhyolitic tuff of upper segment represents the forming age. The two peak ages of 304 Ma and 450 Ma represent the upper limit of the sedimentary event, the forming age of early Paleozoic orogenic belt, respectively, and the 870 Ma represents the age of Neoproterozoic basement. The data of middle detrital rocks indicate that the forming age of Xilimiao Formation was between 304‒282 Ma, older than Zhesi Formation. Provenance of the detrital zircon from the middle Xilimiao Formation provides sedimentary evidence for transform process from compress of the middle Paleozoic orogenic belt to extension of the late Paleozoic rift basin. Key words Xing’an-mongol orogenic; Arigin Sum Area; Xilimiao Formation; Permian; volcanic-sedimentary rock series; zircon geochronology