1 Distributed volcanic fields of the southwestern U.S.

This session invites submissions from various disciplines (e.g., petrology, tectonics, geophysics, geochronology) that explore distributed volcanism in the southwestern U.S. Topics of interest include spatio-temporal trends, magma compositions, and mantle and/or crustal controls on volcanism.

Monday, 18 May 2026
8:00 AM - 12:00 PM
Alvarado A

A Tale of Two Maars: Eruption Triggering Timescales at Potrillo Volcanic Field, New Mexico, USA / Chihuahua, Mexico

Paper number: 1-2
Program: Technical Sessions
Time: 8:25 AM – 8:45 AM

Authors

Abstract

In the Potrillo volcanic field (New Mexico, USA / Chihuahua, Mexico), maar eruptions likely represent the most recent, potentially Holocene, activity within the field. Kilbourne Hole and Hunts Hole are separated by <6 km but differ in dimension, eruptive volume, and xenolith assemblage. We test the hypothesis that Kilbourne Hole was formed by an eruption driven by faster ascent capable of carrying mantle xenoliths.

We analyzed olivine, clinopyroxene, and feldspar crystals from juvenile lapilli hand-picked from surge deposits of the respective eruptions. None of the 130 Kilbourne Hole crystals examined had melt inclusions but 11 contained fluid inclusions, while 20 of the 146 Hunts Hole crystals examined had melt inclusions and ten contained fluid inclusions; two of these had both. The mean CO2 density in primary, carbonate-free fluid inclusions in Kilbourne Hole crystals is 1.0 g/cm3 (corresponding to near-Moho pressures of 8 kbar or 35 km), higher than that of Hunts Hole crystals (0.83 g/cm3; 5 kbar; 20 km). Vapor bubble-free melt inclusions in juvenile Hunts Hole olivine crystals have saturation pressures of at least 2 kbar, indicating degassing. 

Though mantle xenoliths did not surface at Hunts Hole like they did in abundance at Kilbourne Hole, two populations of Hunts Hole olivine compositions emerge, indicating the presence of disaggregated mantle olivine. For both maars, juvenile olivine forsterite contents range from 78 to 88, and CaO contents range from 0.10 to 0.55 wt.%. In contrast, disaggregated mantle xenolith olivines have Fo>89 and CaO<0.15 wt.%. Fluid inclusion data presented in this work are from both olivine populations. Juvenile olivines were targeted for Mg-Fe diffusion chronometry on the outermost core-rim boundary, assuming the Mg-Fe disequilibrium event corresponds to magmas beginning their transit towards the surface. Kilbourne Hole eruption-triggering timescale estimates range from 1.8 to 15 days, and Hunts Hole estimates range from 2.3 to 14 days. These estimates roughly correspond to minimum ascent rates of 0.03 to 0.2 m/s for Kilbourne Hole eruptions and 0.02 to 0.1 m/s for Hunts Hole eruptions. We find that the Hunts Hole mantle xenoliths disaggregated and did not reach the surface in xenolith form, unlike the Kilbourne Hole magmas.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410497

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