Evolution of a Shallow Volcanic Arc Pluton During Arc Migration: A Tectono-Thermal Integrated Study of the St. Martin Granodiorites (Northern Lesser Antilles)

A new data set combining thermobarometry, geo-thermochronology, chronostratigraphic, and structural analyses highlights the tectono-thermal evolution of the St. Martin granodiorite from its emplacement to its surface exposure. The described vertical motions in this part of the upper plate of the Lesser Antilles subduction zone since 30 Myrs are linked to the migration of the Lesser Antilles volcanic arc toward the plate interior. Results suggest that the St. Martin granodioritic pluton emplaced at 4-5 km depth and underwent a four-step history: (a) 30-27 Ma, emplacement along N20-40 degrees transtensive structures oblique to the trench followed by, (b) 27-24 Ma, rapid post-emplacement cooling and exhumation (similar to 0.6 mm/yr) controlled by perpendicular to the trench N45 degrees trending structures, (c) 24-9 Ma, slow subsidence (0.01 mm/yr) and development of carbonate platforms associated to tectonic quiescence, westward migration of the arc, and subsequent cooling of the crust, (d) 9 Ma to present-day, exhumation (similar to 0.25 mm/yr) and uplift of Neogene carbonate platforms mainly along N45 degrees faults that likely accommodate the progressive trench curvature since 30 Ma. Pecube forward modeling using this scenario reproduces both the observed present-day geometry and thermochronometric ages. A similar sequence of events is observed in the Virgin Islands. Along with our new data, this suggests a southward migration of the deformation associated with the opening of the Anegada Trough.

Automated summary

A new dataset has been used to study the tectono-thermal evolution of the St. Martin granodiorite, revealing a complex history of emplacement to surface exposure. The vertical motions in the upper plate of the Lesser Antilles subduction zone and the migration of the volcanic arc are closely linked to this evolution. The four-step history of the granodioritic pluton's emplacement and subsequent cooling and exhumation has been reconstructed, providing insights into the tectonic processes in this region over the past 30 million years.