Exploring the 'Anatomy' of Ocean Crust at Site 1256
In the ‘Superfast campaign’ of the Integrated Ocean Drilling Program (IODP) and the Ocean Drilling Program (ODP) before it, four successive scientific ocean drilling expeditions have come to the same location in the Pacific Ocean (6°44.2'N, 91°56.1'W) to deepen a single "hard rock" drill site: ODP Hole 1256D. Beginning in 2002 with ODP Leg 206, and followed by IODP Expeditions 309 and 312 in 2005, and Expedition 335 in the late spring of this year, these expeditions of the scientific research vessel JOIDES Resolution have combined to deepen this one scientific reference penetration more than 1500 meters into the ocean crust.
Contrary to popular belief, the mantle is not entirely made of magma. Instead, the mantle is solid, though it may partially melt locally (a few % per unit volume). This melting typically occurs about 60 kilometers below mid-ocean ridges, and the magma generated there becomes the gabbros, dikes, and lavas of the crust at the mid-ocean ridge.