Magma source and tectonic setting of the Dunde granite in the Western Tianshan: constraints from geochronology, geochemistry, and Sr–Nd–Hf isotopes

Abstract

The Dunde iron-zinc polymetallic deposit is one of large iron deposits occurred in the Awulale Metallogenetic Belt, Western Tianshan (NW-China). This study reports new geochronology and geochemistry for granite in the Dunde mining area in order to constrain the tectonic-magmatic activities and metallogenesis of this region. Granites in the southwest of Dunde mining area are mainly syenogranites intruded into volcanics of the Dahalajunshan Formation in the Early Carboniferous, and they are far from the area where ore bodies and mineralized altered rocks are widely developed. LA-ICP-MS U–Pb zircon dating indicates that Dunde syenogranite was at 306.8 ± 1.0 Ma, which could constrain the upper limit of metallogenic age for this deposit. The Dunde granites are high SiO₂ (73.41–80.07 wt%), high differentiation index (D.I. = 89.7–95.0), weakly peraluminous to metaluminous (A/CNK = 0.94–1.08), and they are enriched in LILE and LREE and depleted in Eu, Ba, Sr and P₂O₅, indicating that they belong to highly fractionated I-type granite. Based on ε_Hf values (+ 9.2 to + 10.5) for zircon and high ε_Nd(t) values (+ 4.7 to  + 5.8) for whole-rock, and the two-stage model ages for 601–735 Ma, suggest that the magma source could be the juvenile lower crust. Combined with regional geological setting, the 306.8 Ma Dunde granites are formed in post-collision extensional tectonic setting.