Crustal accretion and Paleo-Asian Ocean evolution during Late Paleozoic-Early Mesozoic in southeastern Central Asian Orogenic Belt: Evidence from magmatism in Linxi-Dongwuqi area, southeastern Inner Mongolia

In this paper, the geochronology, geochemistry and isotopic data of Late Paleozoic-Early Mesozoic magmatic rocks in Linxi-Dongwuqi area, Inner Mongolia were systematically collected. Based on the analysis of the temporal-spatial variation of the magmatic rocks and the regional geological data, the evolution of the paleo-Asian Ocean and the crustal accretion in the southeast of the Central Asia Orogenic Belt (CAOB) are discussed. The results show that the Late Paleozoic-Early Mesozoic magmatic rocks in the north and south of Erenhot-Hegenshan ophiolite belt display different activity stages, rock assemblages and geochemical characteristics, ndicating that they belong to different tectono-magmatic belts. The magmatic activity in the north of Erenhot-Hegenshan ophiolite belt lasted from Late Devonian to Middle Permian continuously, and reached its activity peak during Late Carboniferous-Early Permian. The analysis of igneous petrotectonic assemblages shows that the Late Devonian-Carboniferous and Early-Middle Permian magmatism were related to the subduction of Erenhot-Hegenshan oceanic plate under the Uliastai continental margin and the regional extension induced by the upwelling of asthenosphere caused by the break-off of the subducted oceanic plate after the closure of the Erenhot-Hegenshan ocean basin, respectively. The magmatic activity in the south of Erenhot-Hegenshan ophiolite belt is characterized by episodic distribution and can be divided into three periods of Carboniferous, Early-Middle Permian and Late Permian-Triassic generally. And the magmatic front of each period tended to migrate southward with time. Regional geological analysis shows that these three periods of magmatic activity were related to the subduction of the paleo-Asian Ocean plate under the Baolidao island arc, the roll-back of the oceanic plate and the collision orogeny between the Siberian and the Sino-Korean paleoplates after the closure of the paleo-Asian Ocean. Zircon Hf isotopic analysis shows that there was significant crustal accretion during Late Paleozoic to Early Mesozoic in the southeast of the CAOB. The north area of Erenhot-Hegenshan ophiolite belt is characterized by vertical crustal accretion, while the south area of the ophiolite belt is characterized by lateral crustal accretion. © 2022 Science Press. All rights reserved.