Axial summit troughs

Abstract

The axial summit trough is a common feature along the ridge crest of fast-and intermediate-spreading rate ridges and is present along slower-spreading but magma-rich ridges. The trough forms from deformation due to shal-lowly intruded dikes, with deformation accumulating over many years, but the graben dimensions are modified by volcanic deposition from eruptive fissures located within the AST to degrees depending on the frequency and effusion rates of eruptions. The AST, where present, hosts the majority hydrothermal vents along the ridge axis due to its proximity to crustal heat sources (e.g., magma chambers) and anisotropic permeability within the sheeted dikes and tectonically disrupted upper crust. Discontinuities within the AST are coincident with discontinuities in other ridge-crest properties such as depth, axial magma chamber continuity and melt content, and lava geochemistry.