The 89 Ma Tortugal komatiitic suite, Costa Rica: Implications for a common geological origin of the Caribbean and Eastern Pacific region from a mantle plume

Komatiites are reported for the first time in the northern part of the Gulf of Nicoya, Costa Rica. These rocks, dated at 89.7 ± 1.4 Ma (Turonian) by ⁴⁰Ar/³⁹Ar methods, occur as a large, elongated (14 km long, 1.5 km wide) N60°W striking body in the ophiolitic Nicoya Complex. These lavas have high MgO (26%–29%), Ni, and Cr, have high CaO/Al₂O₃ (0.98–1.08) and moderate Al₂O₃/TiO₂ (5.55–8.44) ratios, and are depleted in Al₂O₃ (4%–5.5%), K₂O (0.02%–0.37%), and TiO₂ (0.59%–0.9%). Although these lavas are cumulates, their geochemical composition indicates an origin from a primary komatiitic magma, with a melting temperature of 1700 °C at a depth of 150 km. Similarities in the petrology and age (88–90 Ma) of Gorgona, Curaìao, and Nicoya-Tortugal mafic and ultramafic volcanic rocks suggest that these rocks had a common origin. These occurrences suggest a single hotspot center over a large area of the Caribbean and Eastern Pacific Mesozoic region due to a major thermal anomaly in the mantle, such as a hot, rising, convective plume.