The Early Paleozoic tectonic framework in Weiya area of Central Tianshan Block-Evidence from field geological investigation and zircon U-Pb chronology

Through detailed field work in Weiya area, the authors hold that the main rock assemblage there consists of arc complexes including some metamorphic rocks intruded by post-tectonic granites such as K-feldspar granite. Moreover, these arc complexes were partly metamorphosed and deformed due to the CAOB orogenesis there. Thus, the distribution of metamorphic rocks is limit-ed, and their metamorphic degree has reached greenschist facies with strong cleavage. Sample YM01, YM02 are respectively biotite plagioclase leptynite and amphibolite plagioclase leptynite, and their original rocks are acidic volcanoclastic rocks and diorite, respec-tively. Both zircons of these two samples have recorded the arc magmatic events in northern Central Tianshan Block, suggesting large-scale southward subduction of Tianshan Ocean (part of Paleo-Asian Ocean) between the Ordovician and Devonian. The earli-est subductive processes of Tianshan Ocean from the Late Cambrian indicate that the tectonic transformation occurred in Central Tianshan Block from passive continental margin to active continental margin at that time. Moreover, there are no Precambrian age re-cord in arc complex there. Combined with previous work, the authors hold that at least in Weiya area there must have existed limited Precambrian materials and metamorphic rocks with strong foliations and cleavages, which were probably connected with the orogenic tectonics.