A short-lived but significant Mongol–Okhotsk collisional orogeny in latest Jurassic–earliest Cretaceous

Abstract

The Central Asian Orogenic Belt (CAOB) is one of the largest orogenic collages on Earth, which records a long history of accretionary orogenesis from the late Proterozoic to the Mesozoic. Although paleomagnetic studies have unanimously suggested that the major Mongol–Okhotsk Ocean in the eastern CAOB closed mainly during the Late Jurassic–Early Cretaceous, few conclusive and self-consistent geological studies in Central Asia and East Asia have confirmed the occurrence of this significant collisional orogeny. Based mainly on basin evolution in the CAOB, Tarim Block, North China Block, and Qaidam–Qialian Block during the Late Jurassic–Early Cretaceous, the present study proposes that a short-lived but significant Mongol–Okhotsk collisional event occurred in the latest Jurassic–earliest Cretaceous. The rapid closure of the Mongol–Okhotsk Ocean was possibly related to the clockwise rotation of Siberia, which was driven by the continental collision between the Siberia Craton and the Kolyma–Omolon microcontinent in northeast Russia in the Late Jurassic. Owing to the clockwise rotation of Siberia and the subsequent closure of the Mongol–Okhotsk Ocean, a number of areas to both the east and the west of the Mongol–Okhotsk suture underwent uplift and erosion, including Lake Baikal, Transbaikalia, Sayan ranges, Altai Shan, Junggar Basin, Turfan Basin, Tarim Basin, Tian Shan, Mohe Basin, Great Xing'an ranges, Hailar–Tamsag Basin, Erlian Basin, Songliao Basin, East Gobi Basin, Yingen Basin, Bei Shan, Yin Shan–Yan Shan belt, Ordos Basin, Chaoshui–Yabulai Basin, and northern Qaidam Basin, forming a giant fold and thrust belt in northern China and Mongolia. The collision probably caused a prominent gap between Late Jurassic and Early Cretaceous magmatic episodes in the eastern CAOB and North China Block. After lasting for about 10millionyears, the main portion of the Mongol–Okhotsk Ocean closed, forming a northeast-trending suture. During the Early Cretaceous, a remnant ocean still remained in the easternmost part of the Mongol–Okhotsk Ocean, and the regional compressional setting in East Asia related to the closure of the Mongol–Okhotsk Ocean changed to escape tectonics, driven by the collision of the Lhasa Block at the southern margin of Asia. Strike–slip faulting triggered gravitational collapse of upper crust and delamination of lower crust and mantle lithosphere that was thickened during the Mongol–Okhotsk collision, resulting in the development of a continental-scale extensional setting in East Asia, associated with rift basins, metamorphic core complexes, and igneous rocks.