Paleoproterozoic basement in eastern Central Asia Orogenic Belt:Evidence from granite and sedimentary strata in Sino-Mongolia border area

There are few reports of Archean crystalline basement in the eastern part of the Central Asian Orogenic Belt, which impedes researchers' understanding of ancient tectonic evolution of this area. In this study, the authors discovered Paleoproterozoic fine-grained adamellite and sedimentary rocks (Wulanaobao Formation) unconformably covered by the Niqiuhe Formation of Middle Lower Devonian in the Ulikit Obo area along central China-Mongolia border area. The zircon U-Pb dating results (LA-ICP-MS) show that the crystallization age of monzogranite is 1686 ±10 Ma, formed in Paleoproterozoic. The Ulikit Obo granites are high-K calc-alkaline, peraluminous (A/CNK=1.08-1.11). In combination with the existence of muscovite, the Ulikit Obo granites could be classified as S-type granites. They have positive ε_Hf(t) value(+ 2.9-+ 6.7), which is located lower than the 1.7 Ga crustal evolution trend line; besides, the in-situ Hf isotope two-stage model age of zircon is 2.0-2.3 Ga, so the zircon should be derived from partial melting of pelites in syn-collisional tectonic settings. The Wulanaobao Formation was intruded by the Paleoproterozoic Ulikit Obo granites and their detrital zircons yielded a youngest age peak of ca. 1698 Ma. The discovery of Paleoproterozoic Ulikit Obo granites and Wulanaobao Formation indicates the existence of Paleoproterozoic crystalline basement for the microcontinental massifs in the eastern section of the Central Asian orogenic belt.