Effects of fluids on the accretion and exhumation of young oceanic lithosphere at slower-spreading mid-ocean ridges

Abstract

Fluids, from melt to water to CO2, have a profound effect on deformation of the Earth's crust; yet where the fluids come from, how they are transported, and what physical and chemical processes dominate fluid-assisted deformation remains unclear. This is particularly the case for detachment fault zones that bound oceanic core complexes along (ultra)slow-spreading ridges, where fluid-rock interaction/reaction is argued to directly impact the composition and thermomechanical behaviour of the fault footwall, but for which data are limited. This proposal focuses on investigating the dominant deformation mechanisms that accompany fluid-reaction processes during crustal accretion in a magma-rich environment as a function of strain, depth and temperature (proxy for time) in gabbroic rocks from the Atlantis Bank oceanic core complex (SW Indian Ridge). A combination of light and electron microscopy, and microbeam and mass spectroscopy techniques will be integrated with thermodynamic modelling using an unique combination ofsamples from Hole U1473A (IODP Expedition 360). We will constrain the consequences of fluid-rock exchanges that accompany deformation from hyper-solidus (i.e., melt-present) to ambient conditions. The results of this project will establish the role and impacts of fluid-lubricated deformation on the larger scale rheology in young ocean lithosphere in (ultra)slow-spreadingenvironments near to ridge axes, especially in the highest temperature part of the system that has not previously been wellunderstood or modelled with any existing flow laws.