Geochemical window into subduction and accretion processes: Raspas metamorphic complex, Ecuador

The high-pressure, low-temperature (P = 1.3-2 GPa; T less than or equal to 600 degrees C) Raspas metamorphic complex is an exhumed fragment of the par tially accreted, partially subducted Amotape-Chaucha terrane in southwest E cuador. Comparative analysis of major and trace elements plus Sr, Nd, and P b isotopes in bulk lithologies and individual crystalline phases shows that the complex includes one to three layers of ordinary oceanic crust and und erlying mantle Lithosphere together with oceanic plateau fragments. Subduct ion (and exhumation) of oceanic lithosphere resulted in selective bulk trac e element geochemical changes: Rb, Ba, and Sr have been lost (in amounts fr om approximately 85%-50%) from the high-P, low-T metamorphosed pelites and basalts, whereas Pb is enriched in mafic rocks. During formation of the ecl ogite, U, Pb, and rare earth elements (REEs) were immobile, High-P, low-T m etamorphosed terranes form the basement of active Ecuadorian are volcanoes; partial melting of this basement by mantle - wedge-derived basalt is a lik ely source of adakitic components.