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

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