Tectono-magmatic controls on porphyry Cu endowment in the Carboniferous Dananhu Arc, Central Asian Orogenic Belt: A review

Abstract

Situated in the southwestern margin of the Central Asian Orogenic Belt, the Dananhu Arc is a prominent porphyry Cu belt in NW China. The Carboniferous granitoids that host two giant to large and several medium to small porphyry Cu deposits are concentrated in the middle segment of the arc. In contrast, coeval granitoids in the adjacent western and eastern segments are barren. The key factors controlling porphyry fertility and diversity in this arc have not been well constrained. The geochemical and Sr–Nd–Hf–O isotopic compositions of Carboniferous fertile and barren magmas exhibit systematic variations from west to east along the 600 km-long Dananhu Arc. Fertile granitoids have adakitic affinities, with high Sr/Y ratios, Mg#, and oxygen fugacity (ΔFMQ = +2.53 ± 0.52), and depleted Sr–Nd–Hf–O isotopic compositions. The barren alkaline granitoids in the western segment are characterized by enrichments in large ion lithophile elements, low Mg# and oxygen fugacity (ΔFMQ = +0.31 ± 0.11), and evolved Sr–Nd–Hf–O isotope compositions. The barren calc-alkaline granitoids in the eastern segment have low Sr/Y ratios, moderate Mg# and oxygen fugacity (ΔFMQ = +1.65 ± 0.50), and depleted Sr–Nd–Hf–O isotopic compositions. The fertile adakitic granitoids originated from partial melting of a flat-subducted oceanic slab accompanied by crustal thickening. The barren alkaline granitoids were derived from anatexis of accretionary complexes triggered by slab rollback accompanied by magma migration and crustal thinning. The barren calc-alkaline granitoids were derived from partial melting of the mantle wedge in a normal subduction setting. Taken together, we suggest that distinct tectonic settings generated the heterogeneous distribution of porphyry Cu deposits throughout the Dananhu Arc by controlling the nature of the magma that was generated.