Little is known about fault-rock and fluid rock interactions in West Antarctica because faults are mostly hidden beneath the West Antarctic ice sheet. In the Ford Ranges, Marie Byrd Land, three sites with exposures of brittle faults with tourmaline mineralization offer a rare opportunity to study these interactions. Among these tourmaline-coated faults, some display mirrored surfaces, with slickenlines parallel to aligned tourmaline. Tourmaline and quartz within these planes may provide information on conditions of formation and sources of geothermal fluids within the crust of West Antarctica during tectonism. The fault investigation may add valuable information about sites that localize geothermal heat, in contribution to the effort to improve predictions of future ice sheet stability. We use stable isotope geochemistry and argon-argon (40Ar/39Ar) geochronology to characterize tourmaline formed during brittle faulting to better understand fluid circulation and crustal origins of mineralizing fluids. The oxygen and hydrogen isotope ratios of tourmaline indicate a mix of magmatic- and metamorphic-derived fluids, with a lesser potential for mixing with small volumes of seawater. Preliminary 40Ar/39Ar dates suggest tourmaline mineralization occurred during the Cretaceous Period, a time of regional extension across West Antarctica. In that tectonic setting, fluids likely traveled from deeper within the crust to shallower depths along active brittle normal faults.