Initial Reports of the Deep Sea Drilling Project - Volume 51/52/53

This volume covers Legs 51, 52, and 53 of the cruises of the Drilling Vessel Glomar Challenger. Prior to Legs 51, 52, and 53 of the Deep Sea Drilling Project, four legs in the Atlantic Ocean (Legs 37, 45, 46, and 49) had been devoted primarily to basement drilling. The main objective of these legs, except for Leg 49, was to drill a deep hole in the oceanic crust in order to sample Layer 2 and, if possible, the upper levels of Layer 3. Although basement drilling in the Atlantic Ocean thus far has clearly established the basic composition and extrusive origin of at least the upper third of Layer 2, many important questions remain to be answered: 1) How does Layer 2 vary with depth? 2) What is the nature of Layer 3? 3) How is the oceanic crust constructed? 4) Does the petrology of Layer 2 evolve during construction and change with time? 5) What is the extent and nature of metamorphism in the oceanic crust? 6) What is the nature and extent of sea-water alteration in the crust? 7) What is the source of linear sea-floor magnetic anomalies? To study these problems, the Ocean Crust Panel of JOIDES recommended drilling a deep basement hole in old oceanic crust at the western end of the Atlantic Transect in the vicinity of the Bermuda Rise. The rationale for drilling in old crust was twofold. First, there was reason to believe that drilling would be easier because of infilling, thus increasing the chances for deep penetration; and second, by drilling old crust, we could study the effects of crustal aging. The Bermuda Rise was selected for the experiment since it lies on approximately the same flow line as the deep penetration holes drilled on Leg 45 and Leg 46 and because the basement is anomalously shallow for its age. On the basis of these recommendations, a series of holes was drilled during Legs 51 through 53 at the southern end of the Bermuda Rise. The Glomar Challenger left San Juan, Puerto Rico, on 20 November 1976 to begin Leg 51. The Glomar Challenger returned to San Juan on 17 January 1977 upon completion of the Leg 51 phase of drilling. The ship left San Juan on 22 January 1977 to begin Leg 52. Leg 52 was terminated in San Juan, Puerto Rico, on 8 March 1977. The Glomar Challenger left San Juan on 12 March 1977 to begin Leg 53. Leg 53 ended on 21 April 1977 at Balboa, The Canal Zone.