2008 Joint Annual Meeting (5-9 Oct. 2008): New Ages and Geochemical Data for Gorgona Island, Colombia: A 27 Ma Long History of Mantle Melting in the Formation of the Caribbean Large Igneous Province

The Caribbean Large Igneous Province (CLIP) is the remnant of one or more Late Cretaceous melting anomalies in the Pacific realm. Its origin has been originally ascribed to the initial outburst of the Galapagos plume in Late Cretaceous. However, geologic and geodynamic arguments exclude the Galapagos hotspot as the source of the CLIP (Pindell, 2006) and also cast doubt on the genesis of the province as a result of a mantle plume. Here we present new geochronological and geochemical data on Gorgona Island which support an alternative model for the origin of the island and the CLIP.

Located 50 km off the Pacific coast of Colombia, Gorgona is a tectonic fragment affected by reverse and oblique faulting with a general E to NE vergence, which exposes an ultramafic suite including the world youngest known komatiites. Previous works yielded ages of ~89 Ma (Ar-Ar) and a large spread in radiogenic isotopes and incompatible trace element ratios. More recently it was proposed that the island does not belong to CLIP but would be the result of a plume whose present expression is the Salas y Gomez hotspot (Kerr and Tarney, 2005).

Using laser step heating, we obtained high quality Ar-Ar ages for basalts and gabbros whose range overlap that reported for the CLIP and the western coast of Colombia (92-65 Ma). Our age-controlled geochemical data displays a secular variation from enriched to more depleted composition, shows substantial differences with respect to Salas y Gómez and Galápagos, and overlap with the more primitive CLIP rocks. Accordingly, we propose that Gorgona is part of the CLIP and was produced by several magmatic pulses with progressively higher grades of mantle melting. Thus our results seem to fit better in a scenario of progressive opening of a slab window within an intraoceanic subduction system.