73-9 Understanding Pre-eruptive Magmatic Processes at the Socorro Caldera Complex Using Zircon Geochronology and Geochemistry

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

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Abstract:

The Mogollon-Datil volcanic field (MDVF) in western New Mexico represents a complex of caldera-forming eruptions that occurred during the broader middle Cenozoic ignimbrite flare-up in western North America, a period of intense magmatism linked to the removal of the subducting Farallon slab. Previous geochronological studies utilizing sanidine ⁴⁰Ar-³⁹Ar and zircon U-Pb dating indicate that andesitic to rhyolitic lavas within the MDVF erupted episodically ca. 40-24 Ma, forming clusters of nested and overlapping calderas (e.g., the Socorro-Magdalena complex). The resulting suite of aerially extensive ignimbrites is characterized by chemical zonation, which may reflect magmatic chamber structural features, eruption dynamics, recharge, or a heterogeneous melt source. Precise temporal constraints are essential to refine these processes, and zircon, a common accessory mineral in igneous rocks, serves as a critical tool for geochronological and geochemical investigations of magma.

This study employs high-precision chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb geochronology coupled with inductively coupled plasma mass spectrometry (ICP-MS) trace element geochemistry of zircon to investigate these pre-eruptive magmatic processes. We analyzed six ignimbrite samples formed during eruptive events in the northeastern Socorro-Magdalena caldera cluster that include Lemitar Tuff and underlying Vicks Peak Tuff. Lemitar Tuff samples were collected from different zones of both intra-caldera and outflow facies, while Vicks Peak was located only within the outflow section.

Youngest zircon dates match previously published ⁴⁰Ar-³⁹Ar sanidine eruption ages and improve their precision. The Vicks Peak Tuff erupted ca. 28.7 Ma, with protracted zircon age spectra spanning ca. 250 kyr, whereas the Lemitar Tuff spans ca. 750 kyr and erupted ca. 28.3 Ma. Together, these data indicate a longer zircon crystallization history for the magmatic plumbing system feeding the latter Lemitar Tuff eruption. We anticipate that zircon U-Pb geochronology of the outflow and intra-caldera tuffs, coupled with individual trace element compositions, will provide new insights into magma system evolution and pre-eruptive history in this area.

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

doi: 10.1130/abs/2025AM-9574

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