Age and geochemistry of the Beata Ridge: Primary formation during the main phase (~89 Ma) of the Caribbean Large Igneous Province

The Caribbean Large Igneous Province (CLIP), a Cretaceous oceanic flood basalt province, presumably formed at the initiation of the Galápagos hotspot. During the M81 cruise of the German R/V METEOR, we sampled the Beata Ridge, a prominent submarine structure in the Caribbean Sea belonging to the CLIP. The ridge offers the opportunity to directly sample basement sequences of the central, submarine part of the CLIP, complementing numerous studies of accreted CLIP sequences exposed on land around the margins of this LIP. The majority of the recovered Beata Ridge samples are volcanic, implying that at least parts of the Beata Ridge were formed during a large extrusive event in contrast to previous assumptions that the structure is primarily composed of intrusive rocks. Several stratigraphically controlled profiles were sampled along the western slope of the Beata Ridge using the remotely operated vehicle (ROV) Kiel 6000 and revealed variously alternating sequences of magmatic rocks (lavas, pillow breccias, tuffs and gabbros) and sediment fields. We report new 40Ar/39Ar age and geochemical (major and trace element, Sr-Nd-Hf-Pb isotope) data for the recovered magmatic samples. Although the 40Ar/39Ar analyses display partially disturbed age spectra, they suggest an age range of 92.4–76.9 Ma. Thus our age data show for the first time that the Beata Ridge also formed during the main magmatic stage of the CLIP (~95–83 Ma). Previous studies suggested that the Beata Ridge was formed during a second, lower-volume magmatic phase of the CLIP (~81–71 Ma), possibly related to decompression melting during an extensional phase in the Caribbean. Most samples display relatively flat chondrite-normalized rare earth element (REE) patterns commonly observed throughout the CLIP, but light REE enriched and depleted compositions are also present. The occurrence of enriched and depleted incompatible element and radiogenic isotope signatures implies a heterogeneous mantle source region, as is observed for other LIPs worldwide. Since a high degree of geochemical variability is observed over short stratigraphic intervals within the ROV profiles, melt homogenization did not operate as effectively as commonly assumed for LIPs. Instead the plume head probably preserved some domains of enriched and depleted components. Most of the melts during the main stage have intermediate compositions (with flat REE patterns), representing mixtures of the enriched and depleted components.