The oceanic crust fragments exposed in central America, in north-western
South America, and in the Caribbean islands have been considered to
represent accreted remnants of the Caribbean-Colombian Oceanic Plateau
(CCOP). On the basis of trace element and Nd, Sr, and Pb isotopic
compositions we infer that cumulate rocks, basalts, and diabases from
coastal Ecuador have a different source than the basalts from the
Dominican Republic. The latter suite includes the 86 Ma basalts of the
Duarte Complex which are light rare earth element (REE) -enriched and
display (relative to normal mid-ocean ridge basalts, NMORB) moderate
enrichments in large ion lithophile elements, together with high Nb, Ta,
Pb, and low Th contents. Moreover, they exhibit a rather restricted
range of Nd and Pb isotopic ratios consistent with their derivation from
an ocean island-type mantle source, the composition of which includes
the HIMU (high U-238/Pb-204) component characteristic of the Galapagos
hotspot. In contrast, the 123 Ma Ecuadorian oceanic rocks have flat REE
patterns and (relative to NMORB) are depleted in Zr, Hf, Th, and U.
Moreover, they show a wide range of Nd and Pb isotopic ratios
intermediate between those of ocean island basalts and NMORB. It is
unlikely, on geochemical grounds, that the plume source of the
Ecuadorian fragments was similar to that of the Galapagos. In addition,
because of the NNE motion of the Farallon plate during the Early
Cretaceous, the Ecuadorian oceanic plateau fragments could not have been
derived from the Galapagos hotspot but were likely formed at a
ridge-centered or near-ridge hotspot somewhere in the SE Pacific.