New Mexico Geological Society Annual Spring Meeting — Abstracts

The Black Mountain-Santo Tomas volcanic chain, located in the eastern Potrillo Volcanic Field (PVF) in southern New Mexico, are monogenetic basalts that cover an area of 1295 sq. km and are related to the intracontinental Rio Grande rift. The ~165 ka volcanic chain has at least four main eruptive centers along a north to south trend called Santo Tomas, San Miguel, Little Black Mountain, and Black Mountain, respectively. Previous studies of magma assembly and the extent of monogenetic volcanism within an intra-continental rift system have been focused in central PVF and limited on the eastern PVF. Mapping in the 1960’s identified conflicting numbers of vents/flows at Black Mountain and this project aims to refine the location of vents and flows via detailed mapping, then assess the relationship between this volcanic chain and the larger PVF using whole rock and mineral chemistry analyses.

Recent light detection and ranging data was used to infer the six flow boundaries of Black Mountain using a distal basaltic flow profile. Field mapping will be used to refine these boundaries from the subtle textural changes between the a’ā and the various pāhoehoe comprising this feature and the textures will be used to refine the eruptive styles for these events. This will also be used to identify any differentiation patterns upsection on this feature from each successive eruptive flow. Petrographic data from the main Black Mountain vent reveals a shallow magma chamber with possible magma mixing or recharge from the main source.