Investigating the Origin of the Sierra Quemada Structure, Big Bend National Park, Texas through Geochemical Analyses of Related Igneous Rocks

• Main Author: Leglue, Parker C.
• Language: EN
• Published: University of Louisiana at Lafayette 2019
• Subjects: Geology
• Online Access: http://pqdtopen.proquest.com/#viewpdf?dispub=10814287

<p>The origin of the Sierra Quemada structure, located near the center of Big Bend National Park in Texas, has long been debated. It was originally described as a large igneous pluton by Maxwell et al. (1967) and later as a caldera by publications from Barker et al. (1986), Henry et al. (1986), and Duex et al. (1994). However, more recent publications from the United States Geological Survey (USGS) from Scott et al. (2007) and Page et al. (2008) interpreted the Sierra Quemada structure as a failed caldera without associated collapse. The main objective of this thesis is to investigate relationships between units from outside of the Sierra Quemada structure and units from inside of it by determining the geochemical composition of each sample through X-ray Fluorescence (XRF) analyses. XRF analyses were performed on over thirty samples collected from both inside (I) and outside (O) of the Sierra Quemada, including members of the Chisos Formation such as the Ash Spring Basalt (Tasb), the Bee Mountain Basalt (Tbmb), the Mule Ear Spring Tuff (Tmet), and the Tule Mountain Trachyandesite (Ttmt) as well as ring fracture intrusions (RF), ash flow tuffs (AFT), lithic rich tuffs (LRT), and Chisos Undifferentiated (Tchu). The results of the analyses were plotted on Harker Variation Diagrams that compare SiO2 concentrations to other major elements and oxides that are common in igneous rocks, such as Al2O3, K2O, FeO, Fe2O3, MnO, CaO, TiO2, MgO, and Zr. Harker Variation Diagrams are used to investigate genetic relationships between samples. Some of the diagrams show strong correlations between samples that are suspected to be related, but others show somewhat weaker relationships. These variable results could be attributed to analytical uncertainties from the XRF which are common for elements with atomic numbers (Z) lower than 14 or to variations in lithologic compositions among samples.