The Galapagos Spreading Centre: A Near‐Bottom Geophysical Survey

Abstract

A near‐bottom geophysical survey of the Galapagos spreading centre at 86°W shows the highly lineated nature of oceanic crust generated at a fast‐spreading ridge. The bathymetric relief is dominated by small blocks which tilt slightly away from the spreading centre and which are bounded by inward‐facing scarps. This relief is similar to that found on slow‐spreading ridges, but on a smaller scale, and when covered with a thin layer of sediments, it looks like typical abyssal hill terrain. The magnetization distribution, sediment pattern and the fine‐scale bathymetric structure are used to locate the centre of spreading and the region in which the upper portion of the crust is being formed. Recent volcanic activity is primarily occurring within 2 km of the centre, a region which is nearly sediment‐free and which contains a highly magnetized ridge. Possible models of ridge crest mechanics are constrained by these observations over a ridge spreading with a half‐rate of 35 mm/yr. There appears to be a small median valley which has a width of 16 km and a depth of 150 m. Most of the near‐surface volcanism appears to cease when the rigid blocks are initially faulted apart from the central crustal generation zone at about 2 to 4 km from the centre. The central block is fairly level with a relief which appears to have been formed by constructional volcanism while the rigid blocks on either side of this central one already are tilted slightly outwards and are bounded by inward facing scarps. Copyright © 1974, Wiley Blackwell. All rights reserved