Leg 176 Preliminary Report

CONCLUSIONS

All of the scientific objectives of Leg 176 were dependent on deepening Hole 735B. The ultimate success of the leg will be measured by the results published by the science party and other interested investigators in the years to come. The primary objective of Leg 176 was recovering a representative section of gabbroic Layer 3 to determine its stratigraphic variation with depth. This objective was achieved beyond our expectations, manifested in deepening Hole 735B to more than 1.5 km with an overall recovery of more than 86% in an environment (ultra-slow spreading ridges) where the lower crust is believed to be only about 2 km thick. The supplementary scientific objectives of Leg 176, testing whether or not the Moho is coincident with the crust-mantle boundary and deepening Hole 735B well below the crust-mantle boundary were not achieved due to operational time limitations and drill string failure. Toward these objectives, however, Leg 176 successfully demonstrated that the JOIDES Resolution, with her present technology, has the capacity for deep drilling and high recovery at this location and that the success of Leg 118 was not an anomalous circumstance. We await future drilling programs at this location to fully realize all the science objectives proposed for Leg 176, which include some of the highest order priorities of the Long Range Plan of the Ocean Drilling Program.