Molybdenum and Boron Isotopic Compositions of Porphyry Cu Mineralization‐Related Adakitic Rocks in Central‐Eastern China: New Insights Into their Petrogenesis and Crust‐Mantle Interaction

Abstract

AbstractThe voluminous Late Mesozoic porphyry ore‐related adakitic magmatism in central‐eastern China is crucial to understand the deep geodynamic process of the region and controls on porphyry deposit formation globally. Here, we present a novel study of whole‐rock Mo‐B isotopes on the mineralization‐related adakitic rocks from the Dexing (located in the interior of South China and associated with giant porphyry Cu deposits), and Middle‐Lower Yangtze River (MLYR) (host to one of the largest porphyry Cu‐Au deposit belts) areas in central‐eastern China. The Dexing adakitic rocks have δ98/95Mo ranging from −0.31‰ to −0.01‰ and δ11B from −17.65‰ to −11.49‰. The adakitic rocks from the MLYR area have δ98/95Mo values of −0.5‰ to 0.2‰ and δ11B values of −14.48‰ to −9.53‰. The δ98/95Mo values of both the Dexing and MLYR samples negatively correlate with the La/Yb and La/Sm ratios. Together with the high Mg#, Cr, and Ni contents, these results indicate a process of melt‐mantle interaction resulting in hybridization of initial adakitic melts with low δ98/95Mo and mantle‐derived melts/components with high δ98/95Mo. These adakitic rocks have distinct Mo isotope systematics compared with those of oceanic slab‐derived adakites and MORB‐type eclogites. Their relatively low δ11B values and the lack of correlation between δ11B and B contents support a mafic lower crust source for the initial adakitic melts. We thus suggest that these adakitic rocks were generated by partial melting of delaminated lower crust followed by interaction with the deep mantle, and that melt‐mantle interaction may facilitate Cu‐Mo‐Au mineralization.