Abstract:

The DananhuTousuquan island belt, located along the southern margin of the TurpanHami basin, is an important part of the Central Asian Orogenic Belt and ranks one of the most important metallogenic belts in Xinjiang, NW China. However, its precise formation age and tectonic setting are still controversial. In this study, we identified for the first time a Late Silurian granodiorite in the largest Tuwu Yandong porphyry Cu belt in this island belt. The zircon U - Pb dating indicated that the granodiorite was emplaced at about 420 Ma. The granodiorite is characterized by metaluminous to weakly peraluminous, medium Mg values and calcalkaline compositions; it is enriched in light rare earth elements, Rb, Ba, K, U, Th, and Pb, and depleted in Nb, Ta and Ti; its εNd(t) value is between 4.05 and 4.07, its ISr(t) value is between 0.704149 and 0.704520 and its εHf(t) value is between 8.91 and 11.66. These geochemical data indicate that the magma that formed the granodiorite was produced through partial melting of juvenile crust under the setting of island arc without obvious contamination of ancient continental crust. The discovery of the Late Silurian granodiorite, combined with previous studies, shows that the Dananhu Tousuquan island arc belt and the Harlik island arc belt belong to the same island arc in the Early Paleozoic and constructed an integrated arc basin system with the KalatageXiaorequanzi backarc basin. This knowledge is of great significance to the Late Paleozoic arcbasin evolution of the Eastern Tianshan Mountains.

Key words: Eastern Tianshan, DananhuTousuquan, TuwuYandong, Early Paleozoic, granodiorite