LAS SERIES ALCALINAS DEL PLIOCENO DE COSTA RICA: DISTRIBUCIÓN ESPACIAL Y RELACIÓN CON UNA FUENTE MANTÉLICA TIPO OIB

Abstract

Pliocene alkaline magmatic rocks are reported in the costarican back-arc and paleoarc (AguacateMountains). Teschenites and basanites from Guayacan Formation, are relative high in P2O5, TiO2, Cr, La and Nithan basanites and alkaline basalts from La Garita Formation in the paleoarc, with relative high Al2O3 and Ba.La/Yb and K/Ba ratios evidence an OIB (ocean island basalt) mantelic source. Spider diagrams confirms thatsource, and Ba/La ratios evidence that was subduction modificated.Sr87/Sr86 and Nd134/Nd144 ratios fromGuayacan Formation related the OIB source with a Galapagos Hot Spot trace, the origin of the OIB source canbe interpreted as the remelting of a Galapagos modified mantle or by direct Galapagos Plume enrichment. Localextention poceses, related with transtensional fault system in the central part of Costa Rica facilitated themagma raise.