Tracking the Caribbean magmatic evolution: The British Virgin Islands as a transition between the Greater and Lesser Antilles arcs

The British Virgin Islands archipelago, located between the Greater Antilles and the Lesser Antilles, is a key location to study the geodynamic evolution of the Caribbean plate. Studied samples show typical volcanic arc signatures with calc-alkaline series affinity and strong negative HFSE anomalies concomitant with LILE enrichments. ɛHf values are homogeneous corresponding to a MORB-type mantle. Magmas were sourced from a homogeneous mantle wedge with a less than 2% slab-derived sediment component participation and dominated by aqueous fluids. A concomitant melt component has been detected in the Peter and Norman Islands. U-Pb dating emphasizes an active magmatic period spanning ~13 Ma from 43 to 30 Ma, with a NE/SW decreasing gradient. Thermobarometry data display a SW increasing emplacement depth from 6 to 13 km. Compared to the Greater and Lesser Antilles, this archipelago shows strong similarities with the northern Lesser Antilles extinct arc in terms of source and age. A model of geodynamic evolution is proposed in which this archipelago represents a transition between the Greater and the Lesser Antilles arcs. The Oligocene cessation of magmatism at ~30 Ma may coincide with a regionally documented lull in arc magmatic activity, during which the Bahamas bank collided to the north. Paleomagnetically documented motion of a northeast Caribbean forearc sliver thus occurred that moved the archipelago from a position above the Lesser Antilles subduction zone towards the modern location adjacent to a highly oblique, strike-slip dominated plate boundary, which prevented arc magmatism from restarting again in this part of the Caribbean region.

Keywords: subduction, arc magmatism, U-Pb geochronology, geochemistry, isotope, geodynamic, British Virgins Islands, Caribbean