Spatial distribution of damage around faults in the Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah: A mechanical analog for faulting in pyroclastic deposits on Mars

Abstract

Volcanic ash is thought to comprise a large fraction of the Martian equatorial layered deposits and much new insight into the process of faulting and related fluid flow in these deposits can be gained through the study of analogous terrestrial tuffs. This study identifies a set of fault‐related processes that are pertinent to understanding the evolution of fault systems in fine‐grained, poorly indurated volcanic ash by investigating exposures of faults in the Miocene‐aged Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah. The porosity and granularity of the host rock are found to control the style of localized strain that occurs prior to and contemporaneous with faulting. Deformation bands occur in tuff that was porous and granular at the time of deformation, while fractures formed where the tuff lost its porous and granular nature due to silicic alteration. Non‐localized deformation of the host rock is also prominent and occurs through compaction of void space, including crushing of pumice clasts. Significant off‐fault damage of the host rock, resembling fault pulverization, is recognized adjacent to one analog fault and may reflect the strain rate dependence of the resulting fault zone architecture. These findings provide important new guidelines for future structural analyses and numerical modeling of faulting and subsurface fluid flow through volcanic ash deposits on Mars.