No abstract

No abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to The Journal of Geology. A B S T R A C TField 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.