Geology

Missing (Tectonic) Link

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Science  20 Sep 2002:
Vol. 297, Issue 5589, pp. 1959
DOI: 10.1126/science.297.5589.1959c

The Galapagos Islands were formed by a mantle plume, or hot spot, whose earlier history is written in tracks on the Pacific seafloor that begin at the islands and terminate against the deep-sea trenches west of Central America and Ecuador. Geochemical evidence suggests that the hot spot also gave rise to the magmatic outpouring that, some 72 to 95 million years ago (Ma), formed the Caribbean large igneous province (CLIP), the oceanic plateau that became the Caribbean plate. Yet the oldest known rocks of the Galapagos hot spot tracks in the Pacific date to 15 Ma. That leaves more than 55 million years of the hot spot's record unaccounted for—and presumably subducted away.

Hoernle et al. studied a previously undated Pacific seamount and accreted igneous rock complexes on the coasts of Panama and Costa Rica, and have potentially discovered a direct tie between the hot spot and CLIP. The suite of samples, similar geochemically to both CLIP and Galapagos rocks, neatly spans the previously missing age range between the oldest hot spot traces and the youngest CLIP samples, providing a tangible geologic link between the two now-separated areas. The continuous 95-million-year history of the Galapagos hot spot probably played a key role in the formation of land bridges that helped to drive biotic exchange and evolutionary patterns in the Americas during the late Mesozoic and Cenozoic eras. — SW

Geology30, 795 (2002).

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