Award Date

1-1-2005

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Eugene I. Smith

Number of Pages

94

Abstract

Five calderas were discovered in the northern Kawich Range, central Nevada. These calderas are filled with intracaldera rhyolite tuffs and caldera collapse breccias. Based on 40Ar/39Ar dating of sanidine and crosscutting relations, the calderas erupted in the following order from oldest to youngest: Clifford Spring (23.67 +/- 0.09 Ma), Tobe Spring (22.77 +/- 0.07 Ma), Cow Canyon (22.78 +/- 0.07 Ma), Bellehelen (22.87 +/- 0.16 Ma), and Warm Springs. Welded tuff lithologies of collapse breccia blocks show that these calderas represent separate events and not a single caldera with piecemeal collapse. Geochemistry shows that the five intracaldera tuffs are chemically similar and therefore cogenetic. The five tuffs are also similar to the Pahranagat Formation and the Pyramid Spring tuff. To explain the eruption of at least seven tuffs of very similar chemistry over a period of 1.06 m.y, a new model for magma production in northern Nye County during the Tertiary ignimbrite flare-up is presented. This model calls for a heat surge producing greater than 50 % partial melting of the lower crust producing rhyolitic melt batches of similar chemistry. Cooling of the crust due to these voluminous eruptions resulted in the suppression of the ignimbrite flare up.

Keywords

Caldera; Central; Kawich; Nested; Nevada; Northern; Range

Controlled Subject

Geology

File Format

pdf

File Size

3092.48 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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