U/Pb LA-MC-ICP-MS zircon geochronology and geochemistry from a postcollisional biotite granite of the baja guajira basin, Colombia: Implications for late cretaceous and neogene caribbean-south American tectonics

U/Pb LA-MC-ICP-MS zircon ages and whole-rock geochemistry from a biotite granitoid, recovered at ∼2.1 km depth from the Ranchería-2 well in the Baja Guajira basin, southern Caribbean region, reveal the existence of a ca. 70 Ma silicic plutonic event. This granitoid intrudes ca. 76-80 Ma intraoceanic arc fragments and continental margin sediments that experienced continental subduction and collision since ca. 76 Ma. The major compositional shift recorded by this granitoid, including light rare earth element (LREE) enrichment ([La/Yb] p11.28), the increase in the arc N maturity and its postcollisional affinity, suggests that this magmatism may have been formed during the waning stages of collision due to slab break-off that followed the end of the continental subduction. This interpretation would constrain arc-continent collision of the allochthonous Caribbean plate with this segment of the continental margin by ca. 70-76 Ma. Contemporaneous and slightly diachronous accretionary events are seen along most of the northwestern South American margin. We therefore suggest that the oblique geometry of the Caribbean-South American plate interactions facilitates the accretion of the eastern and northern segments of the oceanic plate margins. Unconformable contact with Late Oligocene-Early Miocene sediments suggests that the granitoid and its host rocks were uplifted and exhumed between the Late Maastrichtian and the Late Oligocene as a consequence of the major changes on the Caribbean-South American convergence.