36-10 The Potential for obtaining reliable Quartz ages using 40Ar/39Ar Geochronology: An example from the Amalia Tuff, North Central New Mexico

Session: Cordilleran Mineral Systems: Interdisciplinary Perspectives on Critical Metal Ore Deposits (Posters)

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Abstract:

⁴⁰Ar/³⁹Ar geochronology has advanced substantially over the past three decades with improvements in mass spectrometry and mineral separation techniques. Despite these advances, many volcanic rocks—particularly those containing altered feldspars, amphiboles, and biotite—remain difficult to date reliably unless zircon is present. Recent developments exploring quartz as a potential geochronometer offer a promising alternative for constraining the ages of both altered and unaltered volcanic rocks, thereby improving reconstructions of their magmatic and geologic histories.

Here we present preliminary ⁴⁰Ar/³⁹Ar analyses of single-crystal quartz and sanidine from the Amalia Tuff of the Questa caldera, north-central New Mexico, which has a published age of 25.39 ± 0.04 Ma. Sanidine total fusion analyses yielded an age of 25.43 ± 0.02 Ma, while single-crystal incremental heating experiments on four sanidine grains produced plateau ages ranging from 25.34 ± 0.04 to 25.48 ± 0.05 Ma. Quartz total fusion analyses yielded ages of 25.25 ± 0.20 Ma from 30 crystals and 24.12 ± 0.31 Ma from 17 crystals.

Additional quartz, sanidine, and other mineral phases from volcanic rocks at other localities are currently being prepared to further assess the feasibility and reproducibility of quartz ⁴⁰Ar/³⁹Ar dating. Continued work is required to identify and quantify sources of radiogenic versus excess argon, particularly in quartz-hosted K-rich fluid inclusions and mineral inclusions.

This approach has important implications for dating mineral deposits, including orogenic and epithermal quartz veins, where conventional mica-based geochronology may yield discordant or unreliable ages due to alteration or imprinting of multiple mineralization events. Quartz geochronology may therefore provide improved constraints on the timing of ore formation and overprinting processes.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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