The formation and evolution of ancient blocks in Xinjiang

Abstract：Four Precambrian block, i.e., Kuruk Tag-Tarim, Central Tianshan, Yili and Kepin, were recognized in Xinjiang on the southern margin of Central Asian orogenic belt. Studies show that (1) the Central Tianshan block has a close affinity with Tarim- Kuruk Tag block , as evidenced by similar pre-Nanhua basement, similar rock assemblages and tectono-magmatic evolutionary processes, implying that Kuruk Tag might be connected with Central Tianshan, and that the Kuruk Tag and Central Tianshan blocks were parts of the Tarim craton during Proterozoic period; (2) the Central Tianshan is a sub-block which was split from the northern Tarim craton during Neoproterozoic Nanhua period, and the Paleozoic Southern Tianshan oceanic basin was developed between the two blocks; (3) the Yili block was similar to the Tarim craton before Neoproterozoic Nanhua period in such aspects as rock assemblages, stratigraphic sequences, tectonic settings and evolution, showing some affinities for Tarim craton. After Nanhua period, geological differences between two blocks became obvious, and in Paleozoic, the Yili block might be linked with the Balkhash block, and in Silurian, two blocks amalgmated; (4) the Kepin block is an oceanic crustal terrane completely different from Kuruk Tag, Central Tianshan and Yili blocks in terms of rock assemblages, stratigraphic sequences, ages and evolutional history. Evidence from geological, magmatic and geochronological features and distribution of detrital zircon U-Pb ages show that Precambrian blocks (Kuruk Tag-Tarim, Central Tianshan, Yili and Kepin) of the northern Xinjiang region recorded abundant information of crustal deformation and magmatism during the early evolution of the Earth, suggesting a strong response to the global polyphase tectonic and magmatic events, including growth of the global continental core, assembly of the global Columbia, and assembly and breakup of the global Rodinia supercontinent. In contrast to the Kuruk Tag-Tarim, Central Tianshan and Yili blocks, the Kepin block preserved some records of the assembly event of Gondwana.