Geochemical differences between the subduction-and collisional-type ore-bearing porphyric rocks
俯冲型和碰撞型含矿斑岩地球化学组成的差异

Porphyry Cu-Mo-Au deposits occur not only in an arc setting, but also in a collisional belt. These ore-bearing porphyries in different tectonic settings have distinctly different geochemistry in trace elements, implying that they have different compositions in source or dynamic mechanisms. Comparing with collisional-type ore-bearing porphyries, the subduction-type rocks have obviously high HREE and Y concentrations, low Sr/Y, (La/Yb)N and (Dy/Yb)N ratios, suggesting that their source are mainly consisted of amphibole but less or no garnet. Although some of subduction-type ore-bearing porphyric rocks have somewhat adakitic geochemical signature, most samples show characteristics similar to the normal arc volcanic rocks, which are likely the product of mantle wedge, metasomatically enriched during slab subduction, through MASH (melting-assimilation-storage-homogenization) process. The collisional-type ore-bearing porphyric rocks clearly have characteristics of typical adakites, which be likely related to the earlier episodes of subduction in their source. The geochemistry of major and trace elements of ore-bearing porphyric rocks in Pulang-Xuejipin is similar to that of the subduction-type. They are likely the products by partial melting of metasomatized mantle wedge by subduction fluid or sediment, trigged by slab break-off of westward-subduction of Ganzi-Litang Ocean, instead of by direct partial melt of an oceanic slab.