Seminar

It has been recognized that there is a linear correlation between crustal thickness and whole-rock Sr/Y rations of magmatic rocks, which can be used to track changes of ancient crustal thickness. Porphyry-type copper deposits are frequently associated with high Sr/Y magmatic rocks or adakites. However, whether crustal thickness has a role in Cu contents of magmatic rocks is unclear. A global data compilation indicates that intermediate-acidic intrusions are enriched in Cu in thick accretionary orogens, but tholeiites are depleted in Cu. However, volcanic rocks are enriched in Cu in thick collisional orogens. Based on Sr/Y rations, we evaluate crustal thickness of the Yindun Arc during Triassic and Cretaceous time. The southern part of the Yidun Arc preserves abundant Triassic oceanic-subduction-related and Cretaceous continental-collision-related intrusions that have higher Sr/Y and Cu contents, which are attributed to thicker crust. In contrast, the magmatic counterparts in the northern part of the Yidun Arc have lower Sr/Y and Cu contents, which are attributed to thinner crust. The proposed mechanism successfully interprets why Triassic and Cretaceous important porphyry Cu deposits primarily occur in the south, but seldom in the northern part of the Yidun Arc