Neoproterozoic tectonic shift from collisional orogenesis to intraplate extension in the Yili Block, southern Central Asian Orogenic Belt

Understanding the tectonic evolution of the many micro-continents in the Central Asian Orogenic Belt is a complex and controversial issue. One such micro-continent, the Yili Block is characterized by Neoproterozoic magmatic rocks, which can provide important constraints on the tectono-magmatic history of the region. Herein, we present a systematic investigation of the petrology, whole-rock geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes on newly identified leucogranite intrusions and gabbroic dikes in the Wenquan district of the northern Yili Block. Two leucogranite samples yielded zircon U-Pb ages of 983 +/- 9 Ma and 905 +/- 9 Ma, respectively. Both of muscovite-bearing leucogranites have S-type affinities and show distinctive geochemical compositions similar to peraluminous granites. Furthermore, the leucogranites exhibit low Rb/Sr ratios (0.10-0.49) and elevated zircon epsilon Hf-(t) values (+3.04 - +13.59), indicating that they were derived from partial melting of supracrustal pelitic and mafic rocks. In contrast, one gabbroic dike sample yielded a zircon U-Pb age of 779 +/- 5 Ma. The gabbroic samples have distinctly high Th/Yb (1.10-1.68) and low Nb/La (0.37-0.46) ratios, with enrichment in large ion lithophile elements and depletion in Nb, Ta and Ti, implying that they were sourced from a metasomatic subcontinental lithospheric mantle. Integrated with other available data, we propose that the Yili Block underwent continuously collisional orogenesis during the early Neoproterozoic (ca. 983-780 Ma), with a subsequent tectonic shift from collisional to an intraplate extensional setting at ca. 779-776 Ma. A comparable magmatic evolution also occurred in adjacent micro-continents of the Kazakhstan region and northern Tarim Craton, indicating that these micro-continents may have shared a common Neoproterozoic geodynamic evolution.

Automated summary

This study provides systematic investigations on the petrology, geochemistry, and geochronology of the Yili Block in the Central Asian Orogenic Belt. The results reveal the tectono-magmatic history of the region, which underwent continuous collisional orogenesis and subsequent intraplate extensional setting during the early Neoproterozoic. Comparison with adjacent micro-continents suggests a common geodynamic evolution during the Neoproterozoic.