Inter-arc spreading in the Mariana Trough

Abstract

A detailed survey of the axial zone of the Mariana Trough suggests that the area is very similar to the axial zone of a slow spreading ridge crest. The morphology is characterized by a series of rotated fault blocks symmetrical about a central graben interpreted as an axial rift valley. Seismic-refraction results indicate a thick transition layer similar to that under the Mid-Atlantic Ridge and normal oceanic crustal thicknesses. Magnetic anomalies, although very low in amplitude, suggest that symmetrical spreading is occurring about the axial valley at a rate of about 1.5 cm/yr, much lower than previous estimates. A model is presented which allows crustal accretion by processes similar to those at slow spreading ridge crests and suggests frequent ridge jumps associated with the localized stress patterns may be responsible for larger-scale structural complexity.