SANTA ELENA OPHIOLITE, COSTA RICA: A KEY FOR THE MAGMATIC AND TECTONIC PAST OF THE CARIBBEAN REGION

The Santa Elena Peninsula, in the Northwestern Pacific coast of Costa Rica, constitutes one of the few ophiolite complexes in the Caribbean Region. Traditionally it has been associated to the Caribbean Plate formation and emplacement between the North American and South American plates. However we here present new structural, chronologic and geochemical data to support the hypothesis of an older more complex origin for this ophiolite.

Santa Elena Ophiolite comprises an allochthonous nappe of ultramafic lithologies. This overthrusting has emplaced a main fragment of the upper mantle and oceanic crust, represented by the association of lherzolite peridotites cut by diabase dikes, pegmatitic gabbroic veins and a small layered gabbro section. The pegmatitic gabbroic intrusions yielded ages circa 132 Ma and due to the lack of chilled margins we interpret that they intruded the peridotite before it was tectonically obducted, and still hot and plastic. The circa 124 Ma years old diabase dike swarm that intrudes the peridotite, presents a subparallel arrangement which suggests a response to extensional stress, like during spreading and/or fissure episodes of magmatic emplacement. The diabase dikes dated have clear chilled margins, evidencing an approximately 10 Ma time span during which the peridotite cooled down and the tectonic overthrust took place.

Geochemical and isotopic comparisons of the different units and other worldwide cases of ophiolite occurrences show similarities with abyssal and slow spreading ridge type peridotites. The chronology also links Santa Elena Ophiolite with one of the principal ophiolite generation pulses during the Late Jurassic and Early Cretaceous making Santa Elena an exceptional key to the understanding of the magmatic and tectonic past in the Caribbean region.