Glass-rich basaltic sand and gravel within the oceanic crust at 22°N

Abstract

DURING Leg 46 of the Deep Sea Drilling Project (January 29–March 10, 1976), the second leg of the International Phase of Oceanic Drilling, the Glomar Challenger drilled into 255 m of basaltic basement at hole 396B, 160-km east of the Mid-Atlantic Ridge valley at 22°59.14′N, 43°30.90′W. The hole was drilled into crust with a magnetic anomaly age of ∼ 10 Myr. This site is located in a N–S trending sediment pond which measures ∼ 4 km × 10 km and is concordant with local topographic trends. There are 150 m of sediment at the drill site; however, the basement slopes regionally to the east and sediment thickness is probably > 250 m along the fault-bounded (?) eastern margin (G. M. Purdy, unpublished, and report of work by the Soviet research vessel Akademik Kurchatov). The bottom 90 m of this hole contained basaltic sand and gravel. This material is not believed to be a drilling artefact, but caused by in situ spalling or brecciation of basaltic pillow rinds.