Deep Sea Drilling Project (DSDP) hole 504B located in the eastern equatorial Pacific, 201 km south of the Costa Rica Rift (CRR), is unique in several ways. Hole 504B extends 1.35 km below the seafloor, which is at a depth of 3.46 km; it has penetrated seismic layers 2A, 2B, and part of 2C and for the first time has provided a very complete section; and it has bottomed in what has been interpreted as a true ophiolite complex. These results constitute for the first time long awaited confirmation of accepted models upon which most oceanic crust theory has been based.
A recent report of DSDP Hole 504B noted that ‘… one is led to question the validity of using ophiolite as models of ocean crust’ (Nature, December 16, 1982). That statement was representative of the state of uncertainty that existed before the hole was drilled. The drill site is located on magnetic anomaly 3′, which has an age estimate of 6.2 m.y. The location, south of the CRR, lies on the easternmost arm of the Galapagos Spreading Center, ideally situated over ophiolite lithostratigraphy, if most current models of the oceanic crust are correct. Hesitation with the acceptance of these models has arisen in recent years from the rarity of dredged and drilled rocks that can be positively identified as being samples of an ophiolite complex. Hole 504B, being along the southern flank of the CRR, should be a good test case.