Hydrothermal circulation at spreading centers is governed by the thermal regime and permeability structure of young ocean crust; thus, it is inextricably coupled to the volcano-tectonic processes along spreading centers. For virtually all spreading centers the interrelationships between hydrothermal, magmatic, and tectonic processes are poorly known because fine-scale mapping of the sea-floor has been restricted to very small segments of ridge crest. The present recommended award will rectify this situation for a major segment of the East Pacific Rise. Using the ARGO deep ocean search vehicle, the project will acquire both side-scan sonar and bottom photography from a one hundred mile long segment of this spreading center. This region has already been intensively studied using surface geological and geophysical techniques and the overall crustal structure is therefore well known. Objectives of the present project are: 1) to map the location of hydrothermal vents, 2) relate vent distribution to faulting and recent volcanic activity, and 3) determine the effect of ridge discontinuities on volcanic and hydrothermal activity. Data acquired during the survey will also be critical in locating sites for deep sea drilling to sample ocean crust.
