LA-ICP-MS zircon U-Pb dating of the volcanic rocks in the middle section of the eastern Tianshan, andits geological significance

Volcanic rocks of the Tousuquan Formation in the northern part of Dacaotan fault, eastern Tianshan are dominated continuously from, basalt to rhyolite, and mainly of low-K tholeiite series and calc-alk.al.ine series. These volcanic rocks have high Ε capREE (46. 17 × 10- 6 ∼ 134. 6 × 10- 6 ), and compared to primitive mantle, all of these volcanic rocks exhibit relative enrichment in large ion lithophile elements ( Sr, Ba, Th) and depletion in high strength field elements (Nb, Ta) , with higher Th/Ta and Ta/Yb ratios. These geochemical characteristics demonstrate that these volcanic rocks were formed at arc settings with continental basement. In situ zircon U-Pb LA-ICP-MS dating on the magmatic genetic zircon yielded an age of the 322.9 ±6. 4Ma. Combined with former research, we concluded that the volcanic rocks in the two-sided of Dacaotan fault, both were formed at arc settings with continental basement, and have the same tectonic setting in the Carboniferous, suggesting that the whole East Tianshan may be the active continent margin of the Tarim. plate, and was not detached by the Kangguertage fault or the Dacaotan fault.