Timing and tectonic settings of the Late Paleozoic intrusions in the Zhusileng, northern Alxa: implication for the metallogeny

Abstract

The Zhusileng–Hangwula tectonic zone, located in the northern Alxa area, is a key site for understanding the evolution of the Paleo-Asian Ocean (PAO) and related mineral formation. We report the major and trace elements and zircon U-Pb ages of newly discovered mafic and intermediate to felsic intrusive rocks in the Zhusileng area. LA-ICP-MS zircon U-Pb analyses of the Echenghei diabase and Haierhan and Heipingshan granites yielded crystallization ages of 305 Ma, 284 Ma, and 271 Ma, respectively. The Late Carboniferous mafic rocks have high MgO and Fe2O3T contents and low K2O and TiO2 contents, and are characterized by depletion of HREEs and notably negative Nb-Ta anomalies, with enrichment of Rb, Ba, and U, which indicate an enriched mantle source. The Early Permian granites of the Zhusileng area are highly differentiated I-type granitoids sourced from mixing of mantle and crust, are high-K calc-alkaline and enriched in LREEs, and exhibit moderately to strongly negative Eu anomalies. All the intrusive rocks formed in a post-collisional extensional environment, which indicates that the branch of the PAO in the northern Alxa area had closed before the Early Permian. The Cu-Mo/Au mineralization in the Zhusileng area formed in the Middle to Late Permian and is genetically linked to the Late Paleozoic post-collisional rifting magmatism from after the closure of the Paleo-Asian Ocean.