Résumé
Upper plates in subduction zones are prone to record slab dynamics as their strain pattern, uplift-subsidence records and volcanic arc activity accommodate 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. Here we focus on the subduction of a buoyant anomaly that flattens the slab, slows down subduction rate and can even lead to collision and crustal thickening if the anomaly is large enough. Although the accommodation by the upper plate of such episodes is rather well described across colliding zones (Cyclades, Cuba, Tibet), the along strike evolution of the trench from collision to flat slab remains poorly studied. In this frame, the junction between the Greater and Lesser Antilles appears to be an ideal target to track the lateral impact of such collision within the upper plate: indeed, at 56 Ma, the buoyant Bahamas Bank entered the Greater Caribbean subduction zone at its eastern tip and collided with the volcanic arc from West to East diachronically. To the West, along Cuba the collision led to the suture of the subduction zone. Along Hispaniola and Puerto Rico, the upper plate shortening, which is limited to the southeast by the Anegada Trough, accommodated the oblique collision. Combining onshore (structural and geological mapping, 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. 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.