Partial melting of thickened or delaminated lower crust in the middle of eastern China: Implications for Cu-Au mineralization

Field relations, isotope systematics, and plate tectonic reconstructions require that felsic adakites in the Yangtze Block and the Dabie Orogen, eastern China, were not derived from a subducting slab, despite the signature of a mantle component in the contemporaneous mafic adakite hosts of Cu-Au deposits in the same areas. The apparently contradictory requirements are accounted for by ( a) a deep crustal melting origin for barren adakites and (b) a crustal delamination origin, followed by ascent through lithospheric mantle, for adakites associated with mineralization. The crustal delamination process associated with the prospective porphyries duplicates the metallogenically essential aspects of the subduction environment. The importance of adakitic magmas in the genesis of porphyry-style Cu-Au deposits is affirmed by these findings, but the range of prospective tectonic environments is extended to include an important intraplate, postsubduction setting. The porphyries of eastern China demonstrate a previously unrecognized relationship between one particular tectonic environment and porphyry- style mineralization that may occur elsewhere.