Award Date

12-1995

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Eugene I. Smith, Chair

Second Committee Member

Wanda J. Taylor

Third Committee Member

Rodney V. Metcalf

Graduate Faculty Representative

Chih-Hsiang Ho

Number of Pages

205

Abstract

The northern Reveille and southern Pancake Ranges, located in the south-central Great Basin, experienced a prolonged history of Tertiary volcanism. Volcanic activity in this area began with the eruption of large-volumes of ash-flow tuffs from calderas of the central Nevada caldera complex. The Reveille Range and the southernmost portion of the Pancake Range are the site of two calderas that are the sources for the tuff of Goblin Knobs and tuff of northern Reveille Range. The tuff of Goblin Knobs (70.4-75.3 wt.% SiO2) erupted from the caldera of Goblin Knobs (25.6 Ma) and is the thickest (~1700 m) ash-flow tuff in the Reveille and southern Pancake Range. Felsic volcanism ended with the eruption of the tuff of northern Reveille Range (71.4-78.5 wt.% SiO2) from the caldera of northern Reveille Range (absolute age unknown). The caldera of northern Reveille Range is nested within the northern part of the caldera of Goblin Knobs.

Volcanic activity in the northern Reveille Range changed from felsic to mafic in composition between 18.5 and 14 Ma. Mafic volcanism began approximately 14 Ma with the eruption of lithospheric mantle derived basaltic andesites (epsilonNd=-8.21 to -7.21 and 87Sr/ 86Sr=0.7076-0.7081). Between 14 and 6 Ma the mantle source changed from lithospheric to asthenospheric mantle. An asthenospheric mantle source dominated the final phases of volcanic activity between 6 and 3 Ma and resulted in the eruption of two isotopically distinct groups of basaltic lavas (epsilonNd=0.75-4.47 and 3.52-5.35 and 87Sr/86Sr=0.7043-0.7061 and 0.7034-0.7036, respectively). More evolved intermediate volcanism (epsilonNd=3.26-3.83 and 87Sr/86Sr=0.7037-0.7064) occurred between the eruption of the two basaltic groups.

Keywords

Andesite; Basalt; Calderas; Igneous rocks; Lavas; Magmas; Nevada – Nye County; United States – Great Basin; Volcanic ash, tuff, etc.

Disciplines

Geochemistry | Geology | Volcanology

Language

English

Comments

Signatures have been redacted for privacy and security measures.

(Refer to PDF file for exact formulas.)


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