WAS THE EOCENE REORGANIZATION OF THE NORTHERN CARIBBEAN PLATE BOUNDARY FROM THE CUBAN TRENCH TO THE CAYMAN STRIKE-SLIP SYSTEM REGIONALLY OF GLOBALLY FORCED?

The northern plate boundary of the Caribbean Plate (CAR) is a strike-slip system, accommodating relative eastward motion of CAR with respect to North America (NAM). In pre-Eocene times, however, relative motion of CAR with respect to NAM was towards the northeast and associated plate convergence was accommodated at a subduction zone between the oceanic CAR and the Bahamas platform. Between 50-45 Ma, this major relative plate motion change was accompanied by (1) onset of formation of oceanic crust in the Cayman Trough, a pull-apart basin on the modern, E-W plate boundary, (2) ‘soft collision’ of the volcanic arc of Cuba with the Bahamas platform, and (3) a step-wise southward shift of the plate boundary from north of Cuba to south of the Yucatan Basin along increasingly easterly strike-slip faults, ultimately separating the Cuban segment from CAR and welding it to NAM.

The CAR-NAM collision on Cuba is often thought to have triggered the 50-45 Ma plate reorganization, whereby arrest of Cuban subduction and subsequent slab break-off focused slab pull towards the Lesser Antilles. However, as the 50-45 Ma period is known for a global plate reorganization, we studied a recent kinematic reconstruction of the Caribbean region in an absolute plate motion frame. This shows that CAR absolute plate motion was towards the northwest until 40 Ma, and since ~40 Ma, CAR has been stationary relative to the mantle. NAM absolute plate motion underwent a significant change from southwestward to westward around 50 Ma. The 50-40 Ma change in relative CAR-NAM motion is therefore dominated by an absolute plate motion change of NAM, not of CAR. The 50-45 Ma plate reorganization may thus be triggered by a far-field driven change in NAM movement, rather than by the ‘local’ Cuba-Bahamas collision.

We propose that the Cayman Trough started opening due to the change in absolute plate motion of NAM between 50-40 Ma and limited motion of CAR as a result of slab anchoring. The final stages of Cuban subduction were then solely driven by slab pull at the Cuban trench, and did no longer accommodate regional plate convergence, resulting in the soft collision. We identify the determination of age relationships between Cayman Trough opening and arrest of the Cuban subduction zone as key to test the regional or global forcing of the northern Caribbean plate boundary reorganization.