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 Newly Identified Cluster of Young (~50 ka), Near-Primitive Alkali Olivine Basalts at the Eastern Edge of the Springerville Volcanic Field, Arizona.

Paper number: 1-10
Program: Technical Sessions
Time: 10:55 AM – 11:15 AM

Authors

Abstract

The Springerville Volcanic Field (SVF) is a large (>3000 km2) distributed volcanic field located at the southern edge of the Colorado Plateau in Arizona. The SVF has been extensively mapped and characterized by previous workers. Existing ages and geochemistry indicate the SVF erupted in three main phases between 2.1 and 0.3 million years ago. The initial eruptive phase (2.1-1.5 Ma) was dominated by large-volume tholeiitic basalts. Over time, the SVF produced smaller volume alkali olivine basalts with increasingly evolved alkalic compositions (1.5-1.0). The most recent eruptive phase (1.0-0.3 Ma) produced predominantly small volume, explosive alkalic eruptions, with the most recent activity dated at 0.3 Ma.

To refine the eruptive history of the SVF and understand its hazard potential, 80 new samples have been collected for 40Ar/39Ar geochronology, geochemistry, and petrology. Sample collection and analysis was prioritized based on units that provide stratigraphic control in key areas of the existing map or previously undated units, as well as focusing on end-member compositions.

New geochronology results support mapped field relations but indicate that ages for several units are generally younger than previously accepted. Importantly, new ages of ~50 ka on a cluster of cones and flows near the eastern edge of the field are significantly younger than previously recognized. These young ages are consistent with the morphology of the flows and cones that occur on a northeast trending lineament. This lineament and the flows themselves cut across U.S. highway 191, reaching the Little Colorado River near the Sherwood Ranch Pueblo, and are located ~10 miles southeast of St. Johns Dome, a site of active CO2 leakage attributed to magmatic sources.

New geochemistry of the flows indicates they are comprised of near-primitive (9-11 wt% MgO, Ni = 180-250 ppm) alkali olivine basalts (olivine Mg# = 87-89). These geochemical and petrologic characteristics potentially link the young (~50 ka) flows to other nearby flows and to a feature interpreted to be a dike that lies on the same northeast lineament. Future work could focus on determining the ages of these nearby units to refine the eruptive history of this young part of the field.

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

doi: 10.1130/abs/2026RM-410505

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