Late Mesozoic magmatism at Xiaokelehe Cu[sbnd]Mo deposit in Great Xing'an Range, NE China: Geodynamic and metallogenic implications

Abstract

Multiphase Late Mesozoic magmatism is clearly recorded at the Xiaokelehe porphyry CuMo deposit in NE China, including the syn-ore granodiorite porphyry, and post-ore diorite, gabbro, monzonite (porphyry), and granite porphyry. In this study, we present new geological, LA-ICP-MS zircon UPb geochronological and geochemical data on these intrusive units to unravel the tectonic evolution of the Late Mesozoic Great Xing'an Range (GXR). Zircon UPb dating indicates that the multiphase magmatism extended from the Late Jurassic to Early Cretaceous, i.e., 149.4 ± 4.0 Ma (diorite), 148.9 ± 1.4 Ma (granodiorite porphyry), 146.9 ± 4.1 Ma (monzonite), 140.6 ± 3.8 Ma (gabbro), and 139.9 ± 4.3 Ma (monzonite porphyry).Geochemical data indicate that the syn-ore granodiorite porphyry is adakie-like, featured by relatively LILE-enrichments (Rb, Ba, K, Pb, LREEs), high Sr contents (1065–1130 ppm), and elevated Sr/Y (129.9–171.8) and (La/Yb)N (35.12–47.07) ratios, but with HFSE-depletions (Nb, Ta, Ti, HREEs), low Y (6.2–8.7 ppm) and Yb (0.48–0.67) contents. The granodiorite porphyry has relatively higher Mg# values (41–47), depletion of Nb and Ta, low Cr (29.0–31.0 ppm) and Ni contents (9.4–12.6 ppm), as well as enriched SrNd isotope features, indicating that the granodiorite porphyry was derived from an enriched mantle (garnet-bearing) refertilized by subduction-related melts in a post-collision setting, and the magmas were subsequently fractionated during their ascent. The diorite and gabbro may have also derived from the refertilized lithospheric mantle (but without garnet), whereas the monzonite and its porphyry were derived from the lower crust at >40 and < 40 km depths, respectively. Meanwhile, fractionation and crustal assimilation have been important for the diorite, gabbro, and monzonite (porphyry) formation. Combined our study with published ones, we concluded that: (1) the Mongol-Okhotsk Ocean was finally closed in the GXR before the Late Jurassic; and (2) Late Mesozoic magmatism and porphyry CuMo mineralization in the GXR likely occurred in the compressive-to-extensional transition after the collision between the Mongol-SinoKorea and Siberia plates.