Ages and petrogenesis of the Late Mesozoic igneous rocks associated with the Xiaokele porphyry Cu–Mo deposit, NE China and their geodynamic implications

Abstract

The genesis of igneous rocks associated with the newly discovered Xiaokele porphyry Cu-Mo deposit, located in the eastern Erguna Block, NE China, can give insights into the regional geodynamic evolution during the Late Mesozoic. Several ore-bodies have been identified in a granodiorite porphyry stock, which intruded the rhyolite and was subsequently intruded by diorite porphyry and granite porphyry. The U–Pb ages of zircons from rhyolite, mineralized granodiorite porphyry, diorite porphyry and granite porphyry associated with the Xiaokele deposit are 152.5 ± 1.7, 150.0 ± 1.6, 147.9 ± 1.3, and 123.2 ± 1.7 Ma, respectively. The rhyolite and granite porphyry have high SiO2 and low MgO, Cr, Co, and Ni contents. Their isotopic data show negative εNd(t) values of −4.76 to −0.87, initial 87Sr/86Sr ratios of 0.7066 to 0.7134 and positive zircon εHf(t) values of 0.33–5.56, indicating that they were derived from a basaltic lower continental crust. The mineralized granodiorite porphyry is characterized by high Sr/Y values and low Y (3.7–8.0) contents, showing adakite affinity. The low K2O/Na2O (0.51–0.7) ratios, high CaO contents, weakly negative εNd(t) (−1.17 to −0.27), and low zircon εHf(t) (1.49–5.4) values from the adakitic samples indicate that they were derived from the partial melting of an altered oceanic slab together with assimilation of mantle peridotite and crustal materials. The 148 Ma diorite porphyry has high Mg# (51–58), weakly negative and positive εNd(t) (−0.09 to 0.01) values, and lower (87Sr/86Sr)i (0.7055–0.7057) ratios, suggesting an enriched mantle wedge source. Considering the late Mesozoic regional tectonic evolution of the Erguna Block and adjacent area, we propose that the formation of the Xiaokele deposit is linked to the southward flat-slab subduction of the Mongol–Okhotsk oceanic plate during the Later Jurassic-Early Cretaceous.