Initial Reports of the Deep Sea Drilling Project - Volume 84

This volume covers Leg 84 of the cruises of the Drilling Vessel Glomar Challenger. The Middle America Trench transect off Guatemala was first recommended for study on the basis of earlier deep sea drilling experience at convergent margins, which showed that to differentiate among models of accretion, imbrication, erosion, or passive subduction at convergent margins, several conditions should be met: (1) Detailed age resolution is required to demonstrate stratigraphic repetition of a section or its absence; such resolution is easier to achieve in low latitudes where microfaunal diversity is greater than in high latitudes. (2) Oceanic basin sediments on the downgoing plate should be lithologically distinct from the slope deposits; glaciation in higher latitudes results in such a great influx of terrigenous sediments that distinction between sediments of different plates is virtually impossible. The low-latitude diversity, lesser terrigenous sediment source, and relatively rapid convergence rate of the Central American Pacific Margin made this a desirable place to drill. Our major objectives on Leg 84 were (1) to establish the age and structure of the continental framework that forms the landward slope of the Trench off Guatemala, and (2) to study the origin and occurrence of gas hydrate in the marine environment. Leg 84 departed Balboa, Panama on 10 January 1982 and ended 26 February 1982 at Manzanillo, Mexico. During the 47 days at sea, the ship occupied one site off the coast of Costa Rica and five sites off the coast of Guatemala, drilled 11 holes, and steamed 3760 nautical miles.