The main rock unit exposed in the southern part of the Tucson Mountains, Pima County, Arizona, is the Cat Mountain rhyolite. It forms the eastward dipping slope and the western escarpment of the mountain range, capping the large fault blocks which make up the range. Petrographic and radiometric data combine to show that the Cat Mountain rhyolite, as originally defined, consists of two major ash flow eruption sequences. The lower sequence is less uniform and continuous than the highly welded characteristically jointed upper unit. A basal non welded unit is found along the western escarpment, a partly welded transition zone is found between the welded units, and a capping partly-to-non-welded unit is exposed in protected parts of the eastern slope. The volcanic history of the area began with the emplacement of a nuee ardente deposit forming the “chaos” unit. This was followed by two ash flow pulses through the same vents, and the sequence was terminated by the intrusion of spherulitic rhyolite sealing up the vents.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/244087 |
| Date | January 1962 |
| Creators | Bikerman, Michael |
| Contributors | Damon, Paul E., Bikerman, Michael |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Thesis-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the Antevs Library, Department of Geosciences, and the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author or the department. |
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