Chemical analyses of basaltic rocks from the Basic Igneous Complex of the Pacific coastal areas of northern South America clearly demonstrate a consistent tholeiitic affinity for this belt and a geochemical similarity of samples from Ecuador, Colombia, and Panama. The rocks are more like ocean-ridge tholeiites than other varieties, but they have higher than expected K, Sr, and Rb contents. Most probably, alteration has caused these anomalies, but a firm conclusion has been frustrated by the lack of correlation of concentration of these elements with the degree of three types of microscopically observable secondary mineralogic changes in the rocks. The rocks form a bimodal geochemical population, about two-thirds basalt and one-third basaltic andesite; both groups are geographically widespread. The increased geochemical information confirms the correlation of this complex with similar rocks in the Cordillera Occidental of Colombia and Ecuador and the Nicoya Peninsula of Costa Rica.

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