Two new chemical analyses show that tholeiitic lava on the coastal plain of Ecuador is similar to basalt on Nicoya Peninsula of Costa Rica and other basalt found along the Pacific Coast of northwestern South America. Harzburgite is found in the same group of mafic volcanic and intrusive rocks here called basic igneous complex. K:Ar age determinations of basaltic lava in this complex show that igneous activity continued at least until early Eocene, although most of the hypabyssal rocks could be Late Jurassic to Late Cretaceous. Discussion includes possible correlation of the basic igneous complex of Ecuador, the Nicoya Complex of Costa Rica, similar rocks along the Pacific Coast of Panama and Colombia, and the basaltic floor of Nazca plate.

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