Charles A. Anderson
1951
<p><span>The </span>older<span> </span>Precambrian<span> rocks of </span>Arizona<span> include the Vishnu, Yavapai, and Pinal schists, all overlain unconformably by nonmetamorphosed younger </span>Precambrian<span> rocks. The </span>older<span> </span>Precambrian<span> schists, unnamed gneisses, and associated granitic masses crop out </span>in<span> many of the mountain ranges southwest of the Colorado plateau. The stratigraphy and </span>structure<span> of the schists can be unraveled to some extent by detailed mapping, and work now </span>in<span> progress by the U. S. Geological Survey </span>in<span> the Bagdad, Prescott-Jerome, and Little Dragoon areas, is revealing folded structures trending generally northwest to northeast. Earlier work by Wilson </span>in<span> the Mazatzal Mountains revealed southeastward-dipping, low-angle thrust faults of </span>older<span> </span>Precambrian<span> age. </span>In<span> the Bagdad and Prescott-Jerome areas, a variety of igneous rocks, including rhyolite, alaskite porphyry, diorite, and gabbro, were intruded into the schists prior to the widespread invasion of granite. Only one period of orogeny followed by the intrusion of granitic rocks can be recognized </span>in<span> each area studied to date. The degree of metamorphism is not uniform and some of the pre-intrusive rocks are nonfoliated, whereas others are highly schistose. Some of the intrusive rocks, including granite, show the effect of dynamic metamorphism. The grade of metamorphism is low to intermediate, except near the large masses of granite where coarse-grained sillimanite-bearing schists are found.</span></p>
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10.1130/0016-7606(1951)62[1331:OPSIA]2.0.CO;2
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Geological Society of America
Older Precambrian structure in Arizona
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