Tectonic significance of the Xilin Gol Complex, Inner Mongolia, China: Petrological, geochemical and U–Pb zircon age constraints

The Xilin Gol Complex, consisting of strongly deformed and metamorphosed rocks, is exposed as a large tectonic unit within the Central-Asian Orogenic Belt (CAOB). It is located on the Xilinhot-Sonidzuoqi north-dipping thrust belt and near the Solonker suture zone that is widely regarded to record the terminal evolution of the CAOB. Its genesis and tectonic origin are a key to test the existing tectonic models as to whether there was a single arc chain by successive accretion or multiple amalgamation involving some microcontinents. This study reports petrological, geochemical, and zircon U-Pb age data of biotite-plagioclase gneisses from the complex. As migmatization is common in the gneiss, restitic and magmatic components are identified in the gneiss by their petrographic features. Mineral chemistry indicates that the Xilin Gol Complex was subjected to amphibolite facies metamorphism. Three groups of zircons are identified by cathodoluminescence (CL) images and Th/U ratios: (1) the first and most abundant group is of magmatic origin and yields a weighted mean