Age and spreading history of the Cayman Trough as determined from depth, heat flow, and magnetic anomalies

Abstract

The opening of the Cayman Trough records aspects of relative motion between the North American and Caribbean plates essential to accurate reconstruction of Caribbean evolution. Assessment of opening rates based upon basement subsidence analysis as well as magnetic anomaly interpretation shows that the trough may have opened at one third to one half previously proposed rates. Depths to basement show that the crust has subsided away from the present axis in two stages: a younger stage characterized by substantial and asymmetric (greater to the east) subsidence, preceded by an older stage of slight increases of depth with distance. Depth to age relations calculated from subsidence curves which accommodate lateral as well as vertical cooling of the accreting slab indicate that the trough has opened at an overall rate of less than 15 mm/yr since 25–30 Ma and at 20–30 mm/yr prior to 30 Ma. Marine magnetic anomalies show lineations perpendicular to the trough, including a distinct central anomaly, but the pattern is neither well defined nor symmetrical about the present axis. However, partial anomaly sequences can be identified on both sides of the axis, and the distribution of these sequences indicates that spreading may have involved frequent short ridge jumps, mostly eastward. The overall rate of opening as indicated by this interpretation of the magnetics is about 15 and 30 mm/yr since and prior to 26 Ma. Both subsidence and magnetics indicate that the trough opened by at least 45–50 Ma.