Previous   |    Next

doi:10.2204/iodp.proc.304305.205.2009

Introduction

Integrated Ocean Drilling Program (IODP) Expedition 304/305 was a two-stage drilling program that took place in 2004–2005 at Atlantis Massif. The expedition was designed to investigate the processes that control oceanic core complex (OCC) formation and the exposure of lower oceanic crustal and upper mantle rocks in young oceanic lithosphere. Site U1309 is located on the central dome of Atlantis Massif (Fig. F1), ~15 km west of the Mid-Atlantic Ridge at 30°N, where the seafloor coincides with a detachment fault surface. Previous studies (Blackman et al., 1998, 2002) have shown that the footwall at Atlantis Massif is composed of lower crust and upper mantle rocks that are denuded by a detachment fault exposed over an 8–10 km wide, 15 km long area that forms an elongate, doubly plunging domal seafloor morphology. The adjacent block to the east, dominated by basalt, is interpreted as the hanging wall to the detachment fault. The detachment is inferred to continue at a gentle dip (<15°) beneath the eastern block toward the ridge axis.

Two holes were drilled at this site; here we focus on Hole U1309D, which penetrated 1415.5 meters below seafloor (mbsf) with 74% recovery (see the “Expedition 304/305 summary” chapter). The deep penetration of Hole U1309D provides an unprecedented view of the architecture of primitive slow-spreading crust (cf. Ocean Drilling Program [ODP] Hole 735B; Dick et al., 2000).

The primary rock types recovered from the Expedition 304/305 sample suite include, in decreasing abundance, gabbro, olivine gabbro, troctolite, oxide-bearing gabbro, oxide gabbro, gabbronorite, oxide- and olivine-bearing gabbro and gabbronorite, diabase, and felsic veins.

Top of page   |    Previous   |    Next