LARGE NEOGENE SUBSIDENCE EVENT ALONG THE MIDDLE AMERICA TRENCH OFF MEXICO (18-DEGREES-19-DEGREES-N) - EVIDENCE FROM SUBMERSIBLE OBSERVATION

Exposures of pre-Eocene plutonic rocks located along the inner slope o f the Middle America Trench were sampled during deep-sea dives off Man zanillo (lat 18 degrees-19 degrees N) at depths ranging from 3950 m to 2823 m. Fission-track data show a rapid cooling of these plutonic roc ks during the Paleocene. A subaerial unconformity indicates that the p lutonic rocks were exposed after Paleocene time. The presence of upper middle bathyal upper Miocene-lower Pliocene marine sediments above th e unconformity documents a Neogene subsidence event at a mean rate of 0.35 mm/yr. This subsidence indicates subduction erosion along this se gment of the margin.