Award Date

December 2016

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Terry L. Spell

Second Committee Member

Rodney V. Metcalf

Third Committee Member

Shichun Huang

Fourth Committee Member

Dennis Bazylinski

Number of Pages

161

Abstract

The Jemez volcanic field (JVF), New Mexico, is a caldera-forming volcanic field located at the junction of the Rio Grande Rift and the Jemez Lineament. The JVF is one of three large North American caldera-forming systems, including Long Valley, California and Yellowstone Plateau volcanic field, Wyoming, which have been active during the Quaternary. Because portions of the JVF are unusually well preserved, it offers a rare opportunity to study how such systems develop. Insight into the history of caldera-forming systems will contribute to the understanding of their potential future behavior. In the case of Yellowstone and Long Valley, that insight could contribute to more accurate prediction of the future activity of these two potentially active systems. This research focuses on the nature of the Canovas Canyon Rhyolite (CCR). These domes and flows were the product of the first significant rhyolitic volcanism in the JVF, beginning about 13 Ma (Gardner, et al., 1986). Timing of the eruptions; over a ~4 Ma time period, as well as the areal extent (more than 50 km2), make it unlikely that the CCR was produced by one long lived magma system.

Models which describe the formation of silicic caldera-forming systems can be broadly grouped into two categories: A. Those which postulate large, thermally stable, long lived magma bodies which develop chemical and thermal gradients, such as the model developed by Hildreth, (1981) and Halliday, et al., (1989); B. Models in which silicic volcanism is produced by smaller, individual batches of melt (Huppert and Sparks, 1988b). In the second type of model, caldera-forming magma chambers are ephemeral and only occur in the last stage of development of the system, prior to the culminating eruption.

Major and trace element geochemistry trends rule out any of the sampled units having been produced by the same magma system. Nd, Sr, and Pb isotope ratios indicate that the CCR are products of fractional crystallization of associated basalts, with up to 50% crustal assimilation. The CCR best fits model B; a rhyolite produced in small, ephemeral, independent magma systems.

Keywords

Canovas Canyon Rhyolite; Jemez Mountains Volcanic Field; Keres Group; rhyolite

Disciplines

Geology

Language

English


Included in

Geology Commons

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