Award Date
1-1-2007
Degree Type
Thesis
Degree Name
Master of Science (MS)
Department
Geoscience
Number of Pages
127
Abstract
The northern McCullough Range andesites are calc-alkaline and contain phenocrysts of olivine, clinopyroxene, and plagioclase. Although the andesites are similar in major element chemistry, they exhibit wide variations in trace element chemistry. Resulting trace element Harker diagrams show considerable scatter and no discernible petrogenetic trends. On {dollar}\sp{87}{dollar}Sr/{dollar}\sp{86}{dollar}Sr and {dollar}\rm\varepsilon\sb{Nd}{dollar} isotope plots, however, andesites fall into 3 distinct groups: group A {dollar}\rm(\sp{87}Sr/\sp{86}Sr=0.70758{dollar} to 0.7077; {dollar}\rm\varepsilon\sb{Nd}=-6.2{dollar} to {dollar}-{dollar}6.9), group B {dollar}\rm(\sp{87}Sr/\sp{86}Sr=0.7081{dollar} to 0.7083; {dollar}\rm\varepsilon\sb{Nd}=-6.7{dollar} to {dollar}-{dollar}7.4), and group C {dollar}\rm(\sp{87}Sr/\sp{86}Sr=0.70897{dollar} to 0.70904; {dollar}\rm\varepsilon\sb{Nd}=-8.8{dollar} to {dollar}-{dollar}9.8). Geochemical variations, isotopic data and petrogenetic modeling suggest that the andesites in the northern McCullough Range formed primarily from mixing together several different andesitic sources (represented by isotope groups A, B, and C) that are similar in chemistry but isotopically distinct. This proposed model involving mixing of different andesitic end members explains the andesite dominated section observed in the McCullough Range and provides an alternative explanation for andesite petrogenesis in extensional terranes. A preliminary study of Xitle volcano in central Mexico shows similarities to the McCullough Range results. (Abstract shortened by UMI.).
Keywords
Andesites; Examples; Extension; McCullough; Mexico; Nevada; Northern; Petrogenesis; Produced; Range; Regional; Volcano
Controlled Subject
Geology; Geochemistry
File Format
File Size
4904.96 KB
Degree Grantor
University of Nevada, Las Vegas
Language
English
Permissions
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Repository Citation
Boland, Kelly Ann, "The petrogenesis of andesites produced during regional extension: Examples from the northern McCullough Range, Nevada and Xitle Volcano, Mexico" (2007). UNLV Retrospective Theses & Dissertations. 3146.
http://dx.doi.org/10.25669/i2to-c2wp
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