Abstract:

 There are different opinions on the existence of microcontinents in Central Asian Orogenic Belt (CAOB) and on the formation age and original rock property of the widely outcropped Xilin Gol Complex. The Xilin Gol complex comprises geologic bodies of different rock types, different metamorphic degrees, various structural styles and different forming ages. We proposed to disintegrate the Xilin Gol Complex and select the supercrustal rocks there among to be named as “Xilinhot Group”, which are aluminumrich argillaceous clastic rocks with amphibolite facies metamorphism and with volcanic and magnetitequartzite intercalated. The group was emplaced by a metagabbro at 739.6 Ma (SHRIMP age) and by an Stype gneissose tourmaline twomica granite formed during the Ordovician with the zircon metamorphotic cores of UPb ages concentrated in 10051026 Ma. The study of isotopic geochronology also shows that the group was reformed by a series of thermal events later. In combination with the regional tectonic evolution, it is suggested that the Xilinhot Group was possibly formed during the Mesoproterozoic, which may prove the existence of Precambrian metamorphic basement rock series in the region, and provide the corroboration for the existence of Xilinhot microblocks.

Key words: Inner Mongolia, Xilin Gol Complex, Xilinhot Group, SHRIMP