Late Cretaceous granitic intrusions and associated deposits in the Yidun Arc of the eastern Tibetan Plateau

摘要

The Yidun Arc is an important tectonic unit and polymetallic metallogenic belt in the Sanjiang tectono-magmatic belt, in which many Cretaceous (138-75 Ma) granites and associated polymetallic deposits are distributed along a NW-trending belt. The Queershan, Cuomolong, Rongyicuo, and Genie granitic intrusions and the associated Sn-Pb-Zn-Ag polymetallic deposits are distributed in the Changtai and Xiangcheng Arcs, whereas the Xiuwacu, Relin, Hongshan, and Tongchanggou granitic intrusions and the associated Cu-Mo-W deposits are mainly distributed in the Geza Arc. This study presents new zircon U-Pb-Hf-O isotopic data for the Queershan, Cuomolong, Rongyicuo, Genie, Xiuwacu, and Tongchanggou granitic intrusions, combined with the structural analysis of the Xiuwacu granitic complex, to discuss the differences in the petrogenesis and metallogenesis of these granitic intrusions, as well as the geodynamic processes that controlled the formation of the Late Cretaceous intrusions and related deposits. Hf-O isotopic characteristics indicate that the highly fractionated granites (HFG) in the Changtai and Xiangcheng Arcs were mainly derived from the partial melting of metasedimentary crustal materials with a minor input from mantle components, while the I-type granites (IG) in the Geza Arc were predominantly derived from the partial melting of ancient lower crustal material. The spatial distributions of the different types of deposits in the Yidun Arc were probably controlled by the magma sources. Reduced magmas produced by the partial melting of the sedimentary crust in the Changtai and Xiangcheng Arcs are favorable for W, Sn, Pb, and Zn mineralization, whereas oxidized magmas produced by the partial melting of the lower crust in the Geza Arc are conducive to the enrichment of Cu, Au, and Mo. The geochronological data indicate that the emplacement ages of the late Cretaceous granites in the Yidun Arc gradually decrease from north to south (ranging from 106 to 73 Ma), reflecting the southward lateral tectonic migration. The structural analysis of the Xiuwacu W-Mo deposit, in combination with previous studies, demonstrated that the Late Cretaceous granites in the Yidun Arc were likely formed in a regional extensional setting, which was probably related to the slab break-off of the Bangong-Nujiang oceanic slab or the subduction of the Yarlung Zangbo oceanic slab.