Phanerozoic evolution of the Inner Mongolia-Daxinganling orogenic belt in North China: constraints from geochronology of ophiolites and associated formations

The Inner Mongolia-Daxinganling Orogenic Belt (IMDOB), located between the North China and South Mongolia Blocks, consists of several ENE-WSW- to NE-SW-trending zones including dismembered ophiolite blocks, metamorphic rocks and granitoids. Although numerous studies have been carried out on this belt, its tectonic evolution has been a subject of controversy, chiefly because of the lack of reliable geochronological data. Based on a synthesis of newly published geochronological data and our unpublished data for the IMDOB, we define two oceanic basins: Ondor Sum and Hegenshan. The former, probably the main one, was initiated during the Ordovician (>467 Ma) period, whereas the latter, representing a back-arc basin, opened on a pre-Permian basement at, or earlier than, Early Permian times (c. 295 Ma). These two oceanic basins were separated by a magmatic arc (Sunid-Baolidao), and were probably closed simultaneously when the final orogenesis of the IMDOB occurred during the Triassic period (240220 Ma). Importantly, the Triassic timing of the final orogenesis of the IMDOB due north of the North China Craton is essentially coeval with that of the Qinling-Dabie-Su-Lu orogenic belt on the southern margin of the North China Craton. It is inferred that this two-sided subduction-collision scenario in the Triassic may have contributed to the Mesozoic lithospheric thinning event of the North China Craton, although the details are unclear.