Fabric Transitions in an oceanic detachment fault; IODP Expedition 357

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e have known for the last 50 years that Europe and America have been moving apart at about 2cm/yr by processes of seafloor spreading that generate new oceanic crust at the submarine mid-Atlantic Ridge. This is one of the fundamental processes of Plate Tectonics, and has shaped the planet that we live on. Yet because we cannot use standard remote sensing techniques using electromagnetic radiation to study the seafloor, in many ways we know more about the surface of Mars than we do about the floor of the Atlantic!Over the last 12 years improved sonar surveys of the mid Atlantic Ridge have revealed a new mode of seafloor spreading where a significant part of the plate divergence is taken up by slip on long-lived, convex upward detachment faults, rather than mainly by magmatic intrusion. Up to half of the Atlantic seafloor may have formed in this way.New drilling using sea bottom drills in IODP Expedition 357 means that we have better samples of an oceanic detachment fault than ever before. These samples will be studied using scanning electron microscope and electron probe techniques to look for the amount of deformation and the way it is localised by different overprinting alteration assemblages. In this way we will understand better how and why deformation takes place on these faults. These studies will be linked to geochemical and isotopic studies by other scientists to understand the role of seawater derived fluids in localising deformation