Zircon U-Pb age and the geochemistry of the Baishiquan mafic-ultramafic complex in the Eastern Tianshan, Xinjiang province: Constraints on the closure of the Paleo-Asian Ocean

Abstract

The Baishiquan Cu-Ni sulfide deposit is located in the northern part of the Center Tianshan Massif, south of the Aqikuduke-Shaquanzi fault of the Eastern Tianshan Mountains. Ore-body was formed by the magmas and lay within the mafic-ultramafic complex. Zircons from the mineralized gabbro of the orefield yield a crystallization age of 281.2 ± 0.9Ma. These gabbro and peridotites of the Baishiquan mafic-ultramafic complex have high Mg content. With enriched LILE (Rb,Ba,K,Sr), LREE and HFSE (U, Pb), these rocks have negative Ce anomalies and depleted HIFE (Th, Nb, Ta, Ti). These data indicate that the Baishiquan complex has the characters of mantle-derived and arc island magmas. Combined with analyses of the geological and tectonic characters of the Baishiquan complex, we conclude that the Baishiquan complex was formed in an island setting or active margin. This indicates that a subduction event was reasonable in the Eastern Tianshan Mountains in the Early Permian, thus the Paleo-Asian Ocean did not close until the later Early Permian.