Award Date

5-1-2013

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Rodney V. Metcalf

Second Committee Member

Michael Wells

Third Committee Member

Terry Spell

Fourth Committee Member

George Rhee

Number of Pages

72

Abstract

Zircon separates from migmatite samples from the East Humboldt Range (EHR), northern Nevada were U-Pb dated using secondary ionization mass spectrometry. Cathodoluminescence images of zircons show bright anhedral cores with abundant euhedral overgrowths surrounding them.

The overgrowths give U-Pb dates indicating two periods of zircon growth. Inner rims have a Cretaceous age population at 70.6 ± 2.6 Ma. Outer rims give Eocene ages that either fall in to a single-age population at 45 ± 1.3 Ma or are part of a range from 41-31 Ma. Discordant zircon cores have upper intercepts between 1.8 -1.0 Ga.

Cretaceous and Eocene ages are interpreted as recording protracted growth of anatectic zircon during Mesozoic thrust burial and Cenozoic regional extension. McGrew et al. (2000) reported a U-Pb TIMS age of 84.8 ± 2.8 Ma on zircons from the EHR, while Premo et al. (2008) reported ion probe ages of 90-71 Ma from zircons in the same area.

Keywords

Cretaceous geologic period; Eocene geologic period; Migmatite; Nevada – East Humboldt Range; Uranium-lead dating; Zircons

Disciplines

Geology | Volcanology

Language

English


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