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XRD Analysis of Felsic Volcanic Units from the Knight Range, Southwestern New Mexico

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

Presenting Author:

Mason O'Neil

Authors:

O'Neil, Mason J.¹, Stevens, Liane M.², Campos, Marykathryn³

(1) Earth Sciences and Geologic Resources, Stephen F. Austin State University, Nacogdoches, Texas, USA, (2) Earth Sciences and Geologic Resources, Stephen F. Austin State University, Nacogdoches, Texas, USA, (3) Oregon State University, Corvallis, Oregon, USA,

Abstract:

The Knight Range of southwestern New Mexico bears a suite of felsic, extrusive igneous rocks erupted during the Tertiary ignimbrite flareup, but the origins and relationships to nearby volcanic fields like the Boot Heel and Mogollon-Datil remain uncertain. Understanding the lithologies and refining the knowledge of this region’s units may help reconstruct the region’s complex eruptive history. This study uses X-ray diffraction (XRD) to semi-quantitatively identify crystalline phases of samples from the Ash-flow Tuff of JPB Mountain, the Ash-flow Tuff of C-Bar Canyon, the Kneeling Nun Tuff, and the Latite and Andesite of Malpais Hills. Samples were powdered, analyzed via XRD, and classified using a QAP diagram. The JPB Mountain and Kneeling Nun tuffs are rhyolitic and rich in quartz (22-39%) and alkali feldspar (21-52%), while the C-Bar Canyon tuff is dacitic, and the Latite and Andesite of Malpais Hills is a quartz latite, and both contain more plagioclase (19-34%) and orthopyroxene (8-12%). Notably, nepheline (0.91%) is also present in the quartz latite, suggesting the influence of a more alkalic magma source. These variations in mineralogy suggest a cyclic progression from quartz-rich rhyolite tuffs to plagioclase-rich dacites and alkaline quartz latites, consistent with magmatic differentiation. These results help define compositional variations within the Knight Range volcanic units and provide a basis for correlating these units with surrounding volcanic fields. Future work will include thin section petrography and X-ray fluorescence (XRF) analysis to identify textures and determine major and trace element bulk rock geochemistry, advancing our understanding of magma evolution in this understudied region.