Tracking the Caribbean Magmatic Evolution: The British Virgin Islands as a Transition Between the Greater and Lesser Antilles Arcs

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Английский. <div><p>The British Virgin Islands (BVI) archipelago, located between the Greater Antilles and the Lesser Antilles, is a key location to study the geodynamic evolution of the Caribbean plate. Geochemistry of the studied samples reveals typical volcanic arc signatures, including a calc-alkaline affinity, strong negative HFSE anomalies, and LILE enrichment. The ɛHf values are homogeneous, indicative of a MORB-type mantle. Magmas were sourced from a homogeneous mantle wedge with less than 2% slab-derived sediment inputs, 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 over ca. 13 Myr (43-30 Ma), with a NE/ SW decreasing age 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 extinct northern Lesser Antilles arc in terms of source and age. A geodynamical evolution model is proposed in which this archipelago represents a transition between the Greater and the Lesser Antilles arcs. The Oligocene cessation of magmatism (ca. 30 Ma) may coincide with a regionally documented lull in arc magmatic activity during which the Bahamas bank collided to the north. Paleomagnetic evidence of forearc sliver motion along the northeastern boundary of the Caribbean indicates a northward translation of the archipelago from a position above the Lesser Antilles subduction zone to its modern location along the highly oblique, strike-slip-dominated plate boundary, thus preventing the re-establishment of arc magmatism in the eastern Caribbean.</p></div> <div>Plain Language Summary<p>The Antilles archipelago is a 3,000 km-long volcanic arc located in the Caribbean Sea. It is notable for its longevity, active for over 140 million years, from the Greater Antilles to the Lesser Antilles, and for its complexity, providing valuable insights on the dynamics of island arcs and plate tectonics. The British Virgin Islands, located in an intermediate position between the Greater Antilles to the North and the Lesser Antilles to the South, represent a key strategic point to understand the geodynamic evolution of the Caribbean arc. Fifteen samples from seven British Virgin archipelago islands were studied along the main NE-SW alignment. Geochronological analyses give crystallization ages spanning on 13 Ma and ranging from 43 to 30 Ma. Crystallization depths ranged from 6 to 13 km progressing from NE to SW. Geochemical results, including radiogenic isotopes, indicate strong similarities with the extinct arc of the northern Lesser Antilles, both in terms of recorded processes and magma sources. Taken together, these new results support the idea that the British Virgin Islands represent a transition in the history of the Antilles arc, which starts from the Greater Antilles and continues until present in the Lesser Antilles.</p></div>