Age and tectonic setting of magmatic sulfide Cu-Ni mineralization in the eastern Tianshan Orogenic Belt, Xinjiang, Central Asia

Abstract

During the Late Paleozoic, extensive magmatism and associated ore deposits were developed in the Eastern Tianshan Orogenic Belt (the Central Asian Orogenic Belt, NW China). In order to better constrain the petrogenesis of the intrusions in the area, we performed major-and trace-element whole-rock geochemical analyses as well as in situ zircon U-Pb and Hf isotopic analyses from the Xiangshan, Luodong and Poshi batholiths. Voluminous 276-284 Ma ultramafic and mafic rocks (associated with magmatic Cu-Ni sulfide deposits of the same age) have variable Hf isotopic compositions (εHf(t) = -10.3 to +14.3), indicating an origin via the contamination of depleted mantle-derived magma by variable amounts of ancient lower crust. The large mafic-ultramafic complexes were emplaced most likely during closure of the ancient Tianshan Ocean, resulting in the formation of several magmatic Cu-Ni sulfide deposits in the Early Permian times.