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Mineralization in regions of plate convergence is dominantly of the hydrothermal type, either directly associated with high-level (subvolcanic) intrusive bodies or with manifestations of explosive volcanism. In both associations, a strong case can be made for a close connection between mineralization and the processes that operate during generation, emplacement, and solidification of hydrous felsic magmas, whether such magmas are generated from appropriate source rocks in a subduction zone or in the lower continental crust.

The thesis espoused here is that magmas of appropriate compositions, including abnormally high metal, S, and H2O contents, are normal products of partially melting nonporous mafic amphibolites of typical oceanic tholeiite composition in the upper parts of a subducting plate. Furthermore, the depth at which these magmas are generated is fully consistent with the depth to the top of the seismic zone under many volcanic arcs. There is no need, therefore, to call upon abnormally metalliferous source rocks or other exotic genetic schemes to account for the association of mineralization with plate convergence. Hydrothermal mineralization is linked to convergence, as to other tectonic regimes, through hydrous magmas.

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