Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Geological and Atmospheric Sciences

First Advisor

Carl E. Jacobson


The basement rocks of the Eastern Transverse Ranges are composed of undeformed Mesozoic batholithic rocks and Proterozoic and Triassic gneissic rocks. Within the prebatholithic rocks a high temperature/low pressure metamorphic event is preserved. This metamorphism is associated with activity on the Red Cloud thrust system. Gneisses affected by this event possess a northeast-southwest to east-west lineation and north-northwest trending folds in the southern and western Transverse Ranges. Fold asymmetry and c-axis quartz fabrics indicate a west-vergent deformation. In the Chuckwalla Mountains the Red Cloud thrust deformation is also associated with syn-kinematic plutonism. Textures in granitic and leucogranitic gneisses in the granitic gneiss complex of the western Chuckwalla Mountains indicate that they were intruded during the Red Cloud thrust deformation. Their general chemistry is similar to syntectonic intrusives elsewhere. These gneisses in the Chuckwalla Mountains are similar texturally, mineralogically, and chemically with foliated granitic rocks intrusive into a correlative of the Late Triassic Mount Lowe Intrusion in the Little Chuckwalla Mountains. This correlation suggests a Late Triassic age for the Red Cloud thrust deformation;The Red Cloud thrust deformation is locally overprinted by later events. In the southwesternmost Chuckwalla Mountains, the Red Cloud thrust-related foliation is overprinted by a foliation axial planar to a locally strongly developed fold set. These folds trend southwest to west, are sub-horizontal, with gently to moderately inclined axial surfaces. They are generally northwest to north vergent and have a strong crenulation lineation;North-northwest striking, generally right-lateral mylonite zones cut the prebatholithic units in the Little Chuckwalla Mountains, Chuckwalla Mountains, southern Eagle Mountains, and central Hexie Mountains. They are generally less than two meters wide and have greenschist facies assemblages. These shear zones are cut by Cretaceous (?) granodiorites;An east-dipping fault separates quartzites from an overlying plate of 1.2 Ga syenites and mangerites in the southeastern Eagle Mountains. The fault truncates 148 Ma quartz latite dikes and is characterized by east-vergent shear indicators and chloritic breccias.



Digital Repository @ Iowa State University,

Copyright Owner

Clay Edward Postlethwaite



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149 pages

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Geology Commons