Eclogite and omphacitite xenoliths of the Navajo Volcanic Field (NVF) provide a unique opportunity to study processes in an oceanic slab down to subarc depths. However, ambiguities remained about protolith origin, prograde metamorphic conditions, and metasomatic processes, which we address here with new geothermobarometric and in-situ U-Pb data. The earliest garnet (53.4 ± 4.8 Ma), omphacite, and phengite generations yielded c...