Recognition of the Early Paleozoic Wuhuaaobao Forearc Basin and Its Paleogeographic Significance in Sunid Zuoqi, Inner Mongolia

YAN Linjie1, XU Bei1,2,†, ZHANG Jiaming1, WANG Yanyang1

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

Abstract Analysis of sedimentary sequence, material composition and geochronology are used to study a newly discovered epimetarmorphic rock series in Wuhuaaobao area of Sunid Zuoqi, Inner Mongolia, and its paleogeographic significance is also discussed. The epimetarmorphic rock serie is characterized by the interbedded sequence of metavolcanic rock, metasandstone and marble, which contains three cycles and represents an upward-shallowing marine volcanic-sedimentary environment. The presence of multilayer volcanic rocks indicates that they formed during continuous magmatic activity. Zircon U-PB age of the metavolcanic rock is 454.4±4.1 Ma, which is coincided with the magmatic rock ages of early Paleozoic Bolidao island arc belt in the north. Because the serie is located between the Baolidao arc magmatic belt in the north and the mélange belt in the south, its paleogeographic position should be an early Paleozoic forearc basin. Sequence, composition, age and position characteristics of the Wuhuaaobao epimetarmorphic rock serie reveal the presence of the forearc basin in the study area. Two evolutionary stages of the forearc basin have been suggested during subduction and collision, respectively, according to the early Paleozoic strata, magmatic rocks and metamorphic events. Key words Xing-meng Orogenic Belt; Sunid Zuoqi; forearc basin; paleogeography