30 Applications of Igneous Petrology, Geochemistry, and Geochronology to Understanding Earth and Other Planetary Systems

This session invites contributions that explore igneous systems through traditional and nontraditional methods. Studies that link crustal evolution, planetary formation, resource potential, and comparative planetology across temporal and spatial scales are especially encouraged.

Tuesday, 10 March 2026
1:30 PM - 3:30 PM
RCC, 104

A Geochemical and Petrological Analysis of the Basement Rocks of the Mexican Hill Quadrangle, Bighorn Mountains, Wyoming, USA.

Paper number: 30-3
Program: Technical Sessions
Time: 2:15 PM – 2:30 PM

Authors

Abstract

The Mexican Hill quadrangle is part of the batholith region of the Bighorn Mountains in the Wyoming craton, which was exhumed during the Laramide orogeny. Past studies have found an intrusion age of the Bighorns to range over ~200 million years, between ~2.7 Ga and ~2.9 Ga, with multiple igneous pulses of intrusion. This study consists of five different rock types: monzogranite, granodiorite, tonalite, and quartz monzodiorite. There were further discordant mafic dikes scattered around the field area. Petrography reveals evidence of myrmekite, sericitization, epidote and chlorite alteration, and an antiperthitic texture. Whole-rock geochemistry revealed a spread of alkalinity, with samples falling in calcic, calc-alkic, and alkali-calcic fields on an alkali-lime index diagram developed by Frost and Frost (2008).  The felsic intrusives are all plotted within the volcanic arc granites field on the Pearce et al. 1984 tectonic interpretation of granitic rocks diagram. The trace element spider diagram showed a depletion in high field-strength elements and a depletion in heavy rare earth elements. Zircon ages of all samples yielded an average age of 2881 ± 5.6 Ma. This age includes the fine-grained mafic dike in the southeastern corner of the quadrangle. The chemistry and geochronology suggest the Mexican Hill quadrangle is a subduction-zone granite from one intrusion event. 

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411704

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