| Popis: |
Adakites are intermediate or acidic volcanic and plutonic rocks which derive from partial melting of subducted oceanic crust when the subducting slab is young (< 20 Ma) and hot, and at the start and the end of subduction. In the Philippines, most of porphyry Cu and epithermal Au deposits are either spatially and temporally related or cogenetic with these rocks and related magmas (Nb-enriched basalts and adakite-linked andesites). The eastern Luzon arc is an example of an adakite-Cu-Au area that is underthrusted by a young crust. The active arcs in Mindanao and Negros are either related to subduction of young crust or to the initiation of subduction. Adakites and related magmas, therefore, appear to be favorable progenitors of Cu and Au deposition. This could be due either to their high content in hydrous fluids, their susceptibility to crustal entrapment and/or their emplacement within older terranes during the start and end of subduction, such that a hydrothermal convection system is more efficiently established. |
