Geochronological and geochemical characteristics of the Precambrian basement of the Zhusileng-Hangwula tectonic zone: Implications for the nature of the South Gobi microcontinent (Central Asian Orogenic Belt)

Abstract The microcontinents remaining in the Central Asian Orogenic Belt (CAOB) somewhat defined the architecture of the orogen, but not knowing whether they originated from neighboring cratons or exotic cratons hinders our understanding of the architecture and evolution of the CAOB. The South Gobi microcontinent (SGM), a significant component of the middle segment of the southern CAOB, has long been controversial because many questions remain regarding its existence and nature. This study focuses on the Chinese part of the SGM, the Zhusileng-Hangwula tectonic zone (ZHTZ) in northwestern China, to research the nature of the Precambrian basement of the SGM. Systematic field-based zircon U-Pb-Hf isotopic and whole-rock elemental analyses were conducted. The intrusions previously thought to be from Paleozoic time are now known to contain crystalline ages of 1462 Ma, 1365 Ma, and 884 Ma; a large number of ca. 1.4 Ga xenocrystal zircons; and numerous metamorphic zircons with ages of 939 Ma. Additionally, a two-mica quartz schist from the Beishan Group constrains the maximum depositional age to 1130 Ma. When integrated with previous studies, these data indicate that the Precambrian basement of the SGM, represented by the basement of the ZHTZ, underwent tectonothermal events at ca. 1.4 Ga and ca. 0.9 Ga, and deposited extensive late Mesoproterozoic–Neoproterozoic siliciclastic-rich successions. Based on the chronological characteristics of provenance, magmatic events, and Hf isotopic compositions of the Precambrian zircons, the Precambrian basement of the SGM shows tectonic affinity with the basements of the Beishan Orogenic Belt and eastern Central Tianshan Block. This suggests that the basements in the southern CAOB may have experienced a similar Precambrian evolutionary history, which implies that a larger-scale ribbon-like paleocontinent might have existed in the southern CAOB. The basement likely originated from northeastern Laurentia, possibly as a part of the Valhalla orogen, considering the Meso–Neoproterozoic tectonothermal events and extensive late Mesoproterozoic–Neoproterozoic siliciclastic-rich successions. Additionally, the weak tectonic affinity between the southern CAOB and adjacent ancient blocks or cratons suggests that some parts of the southern CAOB might not have been derived from the accretionary evolution of the adjacent cratons that bound it, but rather from the accretion of microcontinents that originated from Laurentia.