Geología y evolución magmática del Arco de Sarapiquí, Costa Rica

Abstract

The Sarapiquí Miocene Arc (22.2-11.4 Ma) is located in northern Costa Rica, Central America. The regional basement is represented by serpentinized peridotites, Albian siliceous pelagites and Paleocene to Middle Eocene turbidites. The units from this arc vary from olivine-bearing basalts to rhyolites, including lavas, pyroclastic deposits and lesser subvolcanic bodies. Based on geological mapping, K/Ar dating and geochemical analysis data the magmatic evolution of the Sarapiquí Arc is established in this paper: 1) Jardín Basalts (22.2 Ma) show a near primary tendency with high MgO, TiO 2 , Ni, Cr, and Nb, high initial La/Yb ratios, and low Ba/La. 2) The Arrepentidos Basaltic-andesites, Chaparrón Pyroclasts, Hito Sar Basalts, Boca Tapada Gabbro, and Chamorro Andesites (17.2-11.4 Ma). 3). Contemporaneous felsic magmas, produced by remelting of pre-existing intrusives, originated the Crucitas rhyolites, characterizated by very high Ba/La ratios and REE patterns that indicate a plagioclase rich, amphibole-bearing source. The Zr/Nb ratios (7-36) show the coalition of a minor OIB source with a dominant MORB source, both modificated by subduction. An inverse model of the source using the REE of the mafic units, show that the mantle composition was a garnet peridotite. U/Th ratios <1, indicate that the mantle metasomatism was produced by subduction of carbonate pelagic sediments. Except the low-degree melts included in the Jardín Basalts, the rest of the units show LILE and Pb enrichments and HFSE depletions , typical of the island arc environment.