| El Valle volcano in Panama, results from the eastward subduction of the Nazca plate underneath the Panama Block. It was dominated by andesitic volcanism during the Miocene (∼10-5 Ma) and silicic (dacitic) volcanism during the Quaternary.; Chemically, the products of El Valle volcano Quaternary volcanism have pronounced depletions in the in HREE, low Y, high Sr, high Sr/Y, low K 2O/Na2O that are best explained by partial melting of a low K garnet-bearing source (e.g. eclogite). This contrasts with the silicic deposits from Costa Rica and Nicaragua that have high K2O/Na2O (and relatively high REEs) characteristic of an evolved source with medium to high-K as starting composition (Vogel et al., 2006).; Partial melting accompanying dehydration of the El Valle volcano Quaternary eclogitic source magmas at the base of thickened crust (e.g. Caribbean Large Igneous Province, CLIP), would produce compositionally appropriate TTG (Tonalite-Trondhjemite-Granodiorite) like granitoids in equilibrium with eclogite residues. This model is a direct way of producing high silica magmas in subduction environments without involving fractionation or more complicated processes. |
