Petrogenesis of magmatism in the Yandong region of Eastern Tianshan, Xinjiang: geochemical, geochronological, and Hf isotope constraints.

The petrogenesis and geodynamic setting of magmatic rocks in Eastern Tianshan, Xinjiang, are attracting increasing attention. This study explores these issues by providing SHRIMP zircon U–Pb dating, and element geochemical and Hf isotope data of magmatic rocks exposed in the Yandong region of Eastern Tianshan, Xinjiang. SHRIMP zircon U–Pb dating data indicate that the magmatic activities occurred around 335 Ma, and that mineralization of the Yandong porphyry Cu deposit occurred during the same period as that of the rock formation in the region or slightly later. All the magmatic rocks in Yandong are sub-alkaline or high-K, calc-alkaline with A/CNK values ranging from 0.91 to 2.70, enriched in K, Rb, and Ba and clearly depleted in Nb, Ta, P, Ti, and Th, and have geochemical characteristics typical of adakites (i.e, high Al2O3, high La/Yb ratios and Sr contents, low Y and HREE contents, and positive Eu anomalies).In situHf isotopic analyses of zircons that had previously been dated by SHRIMP yielded positive initial εHf(t) values ranging from +9.4 to +15.8. We suggest that the Palaeo-Tianshan oceanic crust subducted northward beneath the Dananhu-Tousuquan arc belt during the early Carboniferous, and the Yandong magmatic rocks were induced by partial melting of the subducted Palaeo-Tianshan oceanic slab, subsequently having been hybridized by peridotite in the mantle wedge. The slab melts play a crucial role particularly in the relatively closed magma system responsible for generating the Yandong porphyry Cu deposit. [ABSTRACT FROM AUTHOR]