Investigating Northern Lesser Antilles strain evolution during Eocene
Résumé
Upper plates in subduction zones are prone to record slab dynamics as their strain pattern, uplift-subsidence records and volcanic arc activity accommodates variations of slab parameters in terms of dip, density and rheology. The ANR GAARAnti aims at tracking the timing of land emersions and submersions along the Lesser Antilles subduction zone, which is key to understand the long-term mechanical behavior of this subduction zone. In particular the strain history of the northern Lesser Antilles realm, that makes the junction with the Greater Antilles, needs to be better constrain in order to elaborate paleogeographic models. In this study we combined onshore (structural and geological mapping, PMag sampling, absolute dating and biostratigraphy) and offshore investigations (seismic profiling from the 2017 GARANTI Cruise), we evidence an unprecedently described episode of Mid-Eocene shortening, south of the Anegada Trough. Moreover, we present new paleomagnetic data from the island of St. Barthélemy, indicating a Post Oligocene ~25 counterclockwise rotation that we interpret as an accommodation of trench curvature. After a restoration of the Cayman Trough to the Mid Eocene, the regional compressive structures are interpreted to be the eastward propagation of the compressional domain that accommodated the N-S shortening triggered by the collision of the Bahamas Bank. A crustal-scale cross section drawn from the forearc to the backarc across the thrusts allows us to discuss the origin of crustal thickening, magmatism and tectonics, in the study area.