11 Future Voices in Geoscience- Undergraduate Research Posters

This session is for two-year college and four-year college and university students presenting research posters in any subdiscipline of geosciences. Posters and presentations will be judged for awards.

Monday, 18 May 2026
8:00 AM - 5:30 PM
Alvarado D/E

Mesoproterozoic Crystal Plastic Deformation of the Music Pass Pluton, Sangre de Cristo Range, Colorado

Paper number: 11-17
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Sangre de Cristo Range in southern Colorado contains the Mesoproterozoic Music Pass pluton, exposed between Tijeras Peak and Snowslide Mountain. The predominant lithology is a quartz monzonite emplaced at ca.1.43 Ga, consisting of 50% subhedral microcline megacrysts (0.5–4 cm), 30% subhedral plagioclase, 10% anhedral quartz, and 10% biotite. A pervasive subvertical ENE-WSW-striking foliation has an average strike/dip of 116/81 SSW, but defines a girdle distribution with a minimum eigenvector of 275/67, suggesting folding about a steeply-plunging axis. The average mineral lineation is 258/64. Microstructural analysis indicates subgrain rotation and grain boundary migration dynamic recrystallisation of quartz across the pluton. Electron backscatter diffraction analysis of quartz and hornblende indicates dislocation creep occurred at high temperature (>500°C), consistent with amphibolite grade deformation. A lack of rotation of macroscopic foliation across localized shear zones and predominantly symmetric fabrics along XZ and YZ sections suggest deformation is coaxial dominated, but weakly asymmetric fabrics in some oriented samples may indicate north/northeast side up shear. To evaluate strain geometry, four oriented samples were cut into three mutually perpendicular faces: Perpendicular to foliation and parallel to lineation, perpendicular to foliation and lineation, and parallel to foliation (the XZ, YZ, and XY planes, respectively). Sections were scanned using a flatbed scanner, and both edge fabric ellipse and shape matrix eigenvector analyses were used to calculate 2D R and Phi values. For edge fabric ellipse, two rectangular areas were averaged for each section, maximizing horizontal and vertical area. For shape matrix eigenvector analysis, feldspar grains were traced and uploaded to EllipseFit. For both methods, values were then rotated to reflect the original orientation of the respective sample. Lode’s strain symmetry values (v) range from 0.04–0.35, indicating plane strain to slightly oblate strain. Natural strain (ε) values range from 0.38–0.71. U-Pb geochronology of an apatite separate yielded a date of 1338±15 Ma, which likely records the timing of cooling below ~500–450°C, providing a lower age constraint for deformation. Deformation in the Music Pass pluton likely involved a period of a high temperature (>500°C), coaxial dominated strain under ~NE-SW directed contraction shortly after pluton emplacement (between ~1.43-1.34 Ga), followed by a late-stage subtle folding of foliation about a steeply west-plunging axis. 

 

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

doi: 10.1130/abs/2026RM-410677

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