73-17 Evaluating the Nature of Monogenetic Volcanism in the Eastern Potrillo Volcanic Field, New Mexico: Evidence from Petrography and Mineral Chemistry

Session: Using Volcanic Deposits to Help Us Understand Volcanic and Magmatic Processes (Posters)

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Small-scale monogenetic volcanic centers are conventionally thought to form from the transient eruption of compositionally distinct magmas. These features provide snapshots of magma generation within the broader volcanic field to which they belong. The Potrillo Volcanic Field (PVF), located in southern New Mexico and northern Chihuahua, Mexico, lies along the southern Rio Grande rift and contains >150 geologically young (< 1 Ma) mafic cinder/scoria cones and lava flows, maar volcanoes including the well-known Kilbourne Hole, and Aden shield volcano. While the maar-forming eruptions have received the most attention, relatively little work has focused on the smaller volcanic centers and lava flows.

The Black Mountain-Santo Tomas chain is a series of north-south trending cones and flows located approximately 12 to 15 km east of the main PVF. The four major eruptive centers – Santo Tomas, San Miguel, Little Black Mountain, and Black Mountain – are similar in age and have long been hypothesized to originate from a common magma chamber. New mineral chemistry and detailed petrography reveal that these centers were derived from at least two distinct magmas prior to eruption. While they look similar macroscopically (porphyritic, vesicular, olivine-rich basalts), finer-scale investigations into the proportion of distinctive textures, including skeletal olivine, sector and oscillatory zoned pyroxene, and oscillatory zoned plagioclase, reveal two distinct textural groups. Mineral chemistry analyses further support this division, showing that these textural differences coincide to distinct fractionation trends. Together, the mineralogical and petrographic evidence highlight complexities in magma storage and demonstrates the utility of these methods in unraveling the geochemical evolution of magmas.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6436

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