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    Geologic history of an ash-flow sequence and its source area in the Basin and Range province of southeastern Arizona

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    Author
    Marjaniemi, Darwin Keith, 1940-
    Issue Date
    1970
    Keywords
    Volcanic ash, tuff, etc. -- Arizona -- Chiricahua Mountains Region.
    Geology -- Arizona -- Chiricahua Mountains Region.
    Petrology -- Arizona -- Chiricahua Mountains Region.
    Geology, Stratigraphic -- Tertiary.
    Maps
    Advisor
    Damon, Paul E.
    
    Metadata
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    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by 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.
    Abstract
    The tertiary history of the Chiricahua volcanic field of southeastern Arizona is essentially that of rhyolitic ash-flow deposition and concomitant block faulting in the period from 29 to 25 m.y., as determined by K-Ar analysis. The Rhyolite Canyon ash-flow sheet is the youngest of three sheets, each more than 1000 feet thick. Its distribution is limited mainly to the Chiricahua and northern Pedregosa Mountains with a lesser amount of deposits in the neighboring Swisshelm and Peloncillo Mountains. It is estimated that the original areal extent was of the order of 700 square miles and that the volume of deposits was around 100 cubic miles. The source area of the Rhyolite Canyon sheet is identified as a 13-mile diameter caldera, named the Turkey Creek caldera. This is the first major caldera of the Valles type described in the Mexican Highland and Sonoran Desert sections of the Basin and Range. It is unique because of its denudation. Erosion to 5000-foot depth locally has exposed thick sections of moat deposits and a fine grained monzonite pluton associated with central doming. Rhyolite Canyon tuff in the caldera, some 3000 feet thick, is domed and intruded by the monzonite. More than 1500 feet of tuff breccia, tuffaceous sediments, and rhyolite flows are exposed in the moat, along with 3000 feet of monzonite forming annular segments a couple miles wide abutting or overlying rocks forming the caldera wall. The most monzonite is similar to that in the dome and was emplaced amidst the period of deposition in the caldera. Petrographic and trace element analyses indicate a cogenetic relation between the Rhyolite Canyon sequence and the moat rhyolites. The K-Ar age of the Rhyolite Canyon tuff is very close to that of the monzonite. The ash-flow sheet immediately underlying the Rhyolite Canyon sheet is also very close in age as indicated by K-Ar analyses. Block faulting and tilting took place between the two sheets and also following the deposition of the Rhyolite Canyon sheet. There is evidence that the present basin-range structure was not established until after the Rhyolite Canyon sheet had been emplaced.
    Type
    text
    Dissertation-Reproduction (electronic)
    Maps
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Geology
    Degree Grantor
    University of Arizona
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