Prolonged volcanic history for the Curaçao Lava Formation inferred from new 40Ar-39Ar ages and trace phase geochemistry

Popular models have suggested that the Caribbean Large Igneous Province (CLIP) formed from the initial plume head of the Galapagos hotspot. A key exposure of CLIP lavas is the Curaçao Lava Formation (CLF), a 5 km section of lavas and sills on the island of Curaçao. The CLF contains a broad compositional range of submarine lavas from picrite pillows at the base of the identified section to plagioclase-clinopyroxene tholeiitic lavas, hyaloclastites, and poikilitic sills at the top. Despite the regional significance of the CLF to the tectonic interpretation of the CLIP, only whole rock geochemistry and a few ⁴⁰Ar-³⁹Ar ages exist for Curaçao. These ages suggest formation of the lavas around 89 Ma and the poikilitic sills around 75 Ma. However, Mid-Albian (~110 Ma) fossil ammonites from a single locality of intercalated sediments suggest a considerably older formation for the CLF. This older age of formation has been used to justify alternate formation models for the CLIP to a Galapagos plume initiation. Here we present new ⁴⁰Ar-³⁹Ar ages for the lavas and sills of the CLF that indicate a younger and more extended volcanic history than previously recognized. We have identified lava sequences from several localities on the island that erupted 62-66 Ma as well as lavas and sills that fall within previously recognized age ranges. The youngest ages are obtained on samples directly adjacent to the Mid-Albian ammonite locality. These results suggest that large portions of the CLF (1) significantly postdate initiation of the CLIP, and (2) may not be compatible with an origin related to the initiation of the Galapagos hotspot. It is important to note, however, that the previous 89 Ma ages from Curaçao lavas are closer to ages from CLIP lavas on Haiti that reach 90-94 Ma and are spatially located near the picrites on Curaçao. These diverse ages also require significant reinterpretation of the CLF as a complex association of lavas potentially spanning 30 million years. Considering this complex history, we have examined both the whole rock geochemistry of the CLF and added major and trace element chemistry for major phases (olivine, clinopyroxene, plagioclase) present throughout the CLF using EMPA and LA-ICP-MS. These include both picritic lavas of up to 28 wt. % MgO and olivine with Fo 82-89. The bulk of the tholeiitic lavas and sills, however, have a more restricted range in MgO from 6-10 wt. % and a broad range of plagioclase compositions. We use trace element chemistry preserved in phenocrysts to help identify changing tectonic signatures over the newly identified ~30 million year history of the CLF.