Building the Proterozoic basement of the western Xing'an-Airgin Sum Block in the eastern Central Asian Orogenic Belt and its implications for the Nuna breakup and Rodinia assembly

Abstract

The Xing’an-Airgin Sum Block (XAB) is located in central and northern Inner Mongolia, North China, and belongs to one of the oldest blocks in the Central Asian Orogenic Belt (CAOB). Previous studies have shown that there are Mesoproterozoic granites in the XAB; however, the formation process of the Precambrian basement, and also the tectonic evolution and origin of the block are unclear. In this work, the Mesoproterozoic and early Neoproterozoic stratigraphic sequences, ages and the related sedimentary basin types of the western XAB are reported for the first time. Our study reveals that the Mesoproterozoic to early Neoproterozoic stratigraphic sequence contains the Baoyintu Group and Airgin Sum Group with respective depositional ages of 1516–1392 Ma, and 1237–921 Ma. Sedimentation analysis suggests that the Baoyintu Group and the Airgin Sum Group formed in the coastal marine environment with clastic and carbonate provenances and the shallow marine clastic sedimentary environment, respectively. The age distribution patterns of detrital zircons indicate that there were two different types of sedimentary basins, including two convergent basins formed in ∼ 1400 and ∼ 930 Ma, and a collisional basin developed in ∼ 1237 Ma. However, the 1392–1379 Ma syenogranites and alkali-feldspar granites, which are geochemically similar to A-type granites, were generated by the partial melting of mixed Paleo- and Mesoproterozoic crustal materials in an extensional setting. The newly identified early Neoproterozoic I-type granite (921 Ma) was derived from reworking of the Paleo- to Mesoproterozoic crustal source in a hydrous, garnet-free and plagioclase residual condition. These geochemical signatures, coupled with the three sedimentary stages included on the block, suggest that the 1.4–1.3 Ga period recorded an extensional regime at a convergent continental margin (e.g., back-arc basin), whereas the early Neoproterozoic period was likely controlled by a continental arc setting. In summary, the tectonic evolution process of the XAB documented by three sedimentary and two magmatic events could be its response to the supercontinent cycle from the Nuna breakup to the Rodinia assembly.