Tectonical significance of the Carboniferous volcanic rocks in eastern Tianshan

Abstract

The volcanic rocks of the eastern Tianshan are important for understanding the Paleozoic evolution of Paleo-Asian oceanic. It is bounded to the southern Turfan-Hami basin, and dominated by A'qikekuduke fault. Petrological, isotope chronology and geochemical features of these Carboniferous volcanic rocks show that:(1) They belong to the calc-alkaline series. There are two type of basalt: N-MORB and IAT in eastern Tianshan, which show that these volcanic rocks were formed in a back-are ocean basin tectonic environment; (2) In situ zircon U-Pb LA-ICP-MS dating on the rhyolite zircon of Di' kaner Formation yielded an age of the 320 ± 1.2Ma( MSWD = 1.3) in the southern Turfan-Hami basin. This age is explained as the intrusion age of the pluton ; (3 ) Compared with volcanic rocks of the eastern Tianshan and its neighboring areas, we find that geochemical features of the Carboniferous basalts, at similar SiO2 levels, K2O, K2O + Na2O, K2O/Na 2O, LILE(Rb, Ba, Sr) and HFSE(Nb, Ta, Th, Zr), gradually increase from north to south, show the compositional zone. The geochemical zone is similar to the geochemical polarity in the Mesozoic and. Cenozoic circum-Pacific island arc, allow us to infer that geochemical zone can be attributed to the subduction of the Paleo-Asian oceanic plate under the Junggar- Turfan-Hami plate.