9726885 Reinen It has been known for 30 years that hydrous phases subjected to stress during dehydration at low pressures can develop a mechanical instability leading to faulting. This phenomenon is considered to be the leading candidate to explain earthquakes at depths between 30 and 300km in Earth and a possible mechanism at all depths at which earthquakes exist. The accepted explanation of this phenomenon rests on the assumption that the volume of fluid produced in such dehydration reactions is greater than the volume of the dehydrating phase. It is now known that at very high pressure, the total volume produced by such reactions is actually smaller than that of the parent phase, raising the question as to whether this phenomenon can operate as an earthquake mechanism at depth. This project will utilize unique high pressure instrumentation to conduct deformation experiments on antigorite serpentine under pressures greater than 2.2 GPa, physical conditions such that the total volume of the product assemblage is smaller than that of the dehydrating phase, in order to test whether a mechanical instability can exist under these conditions. It is hypothesized that under these conditions, the primary failure unit will switch from formation of fluid-generated tensile microcracks to formation of fluid- generated compressive microanticracks and that the instability will be preserved. ***
