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

pdf

File Size

4904.96 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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