Did the Turonian-Coniacian plume pulse trigger subduction initiation in the Northern Caribbean? Constraints from Ar-40/Ar-39 dating of the Moa-Baracoa metamorphic sole (eastern Cuba)

摘要

The Guira de Jauco metamorphic sole, below the Moa-Baracoa ophiolite (eastern Cuba), contains strongly deformed amphibolites formed at peak metamorphic conditions of 650-660 degrees C, approximately 8.6kbar (~30km depth). The geochemistry, based on immobile elements of the amphibolites, suggests oceanic lithosphere protholiths with a variable subduction component in a supra-subduction zone environment. The geochemical similarity and tectonic relations among the amphibolites and the basic rocks from the overlying ophiolite suggest a similar origin and protholith. New hornblende Ar-40/Ar-39 cooling ages of 77-81Ma obtained for the amphibolites agree with this hypothesis, and indicate formation and cooling/exhumation of the sole in Late Cretaceous times. The cooling ages, geochemical evidence for a back-arc setting of formation of the mafic protoliths, and regional geology of the region allow proposal of the inception of a new SW-dipping subduction zone in the back-arc region of the northern Caribbean arc during the Late Cretaceous (ca. 90-85Ma). Subduction inception was almost synchronous with the main plume pulse of the Caribbean-Colombian Oceanic Plateau (92-88Ma) and occurred around 15 million years before arc-continent collision (75Ma-Eocene) at the northern leading edge of the Caribbean plate. This chronological framework suggests a plate reorganization process in the region triggered by the Caribbean-Colombian mantle plume.