Age and Geochemistry of the Central American Forearc Basement: Insights into Mesozoic Arc Volcanism and Seamount Accretion on the Fringe of the Caribbean Large Igneous Province

The forearc basement along the Pacific coast of northern Central America (between southern Mexico and Costa Rica) comprises a highly tectonized accretionary assemblage of igneous and ultramafic rocks. Since this region is important for the understanding of the tectonomagmatic evolution of the Caribbean plate, we present new, state of the art 40Ar/39Ar age and comprehensive geochemical data of igneous rocks recovered from the forearc basement during DSDP Legs 67 and 84 off the Guatemalan coast (Chortis Block).

Volcanic and gabbroic rocks with primitive arc geochemical signatures formed between ~100 and ≥180 Ma and are interpreted to have originated by arc magmatism resulting from subduction of the Pacific/Farallon plate. Geochemically enriched ocean island basalt (OIB)-like units are interpreted as accreted seamounts and islands of a 100 to ≥220 Ma old hotspot track, which originated from a hotspot located in the central Pacific. Based on their combined Pb, Nd, Hf isotopic compositions an affiliation of these rocks with the Caribbean Large Igneous Province or the present-day Galápagos hotspot appears unlikely. Rocks of similar age and geochemistry are exposed on the Santa Elena Peninsula in Costa Rica suggesting that a similar forearc basement is accreted to the continental Chortis Block all the way from southern Mexico to Costa Rica.

Tectonization/shearing, amphibolite metamorphism and the timing of secondary thermal overprint of the forearc rocks is proposed to originate from the collision of the Chortis Block with the North American Maya Block in the east and the Caribbean plateau in the south at ~80 Ma leading to compression, and imbrication at the seaward margin of the Chortis Block. The collision transferred the east-directed Farallon plate motion to the Chortis Block resulting in its translation along the sinistral Motagua-Polichic strike-slip fault.