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Chapter 2: Miocene volcanism, folding, and faulting in the Castle Mountains, southern Nevada and eastern California

By
Ryan D. Turner
Ryan D. Turner
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Allen F. Glazner
Allen F. Glazner
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Published:
January 01, 1990

Field, geochemical, and geochronological studies in the Castle Mountains constrain the timing and nature of magmatism, folding, and normal faulting related to Miocene crustal extension in the northern Colorado River trough. Volcanism began at approximately 18 Ma; it evolved from initial production of intermediate-composition lavas to bimodal basalt-rhyolite volcanism and returned to intermediate-composition volcanism after 12.8 Ma. Although these transitions in volcanic style are not sharply defined, the bimodal assemblage apparently was erupted during active extension by normal faulting. Linear compositional trends, disequilibrium textures, and elevated 87Sr/86Sr ratios in silicic rocks indicate that the spectrum of compositions observed in the volcanic rocks was produced by magma mixing accompanied by minor crystal fractionation. These compositional and textural features are similar to those seen in other extension-related magmatic suites of the southwestern United States.

Rocks in the Castle Mountains are folded into a northeast-trending anticline and are cut by east-dipping low-angle normal faults and high-angle strike- and oblique-slip faults. High-angle faults generally cut low-angle faults. The different fault sets may be part of a continuum in which early high-angle faults are rotated to low dips by younger high-angle faults. The anticline involves both Precambrian basement rocks and Tertiary cover. K-Ar dates on the youngest folded unit and on rhyolite plugs, which apparently were intruded during the latest stages of folding, indicate that folding occurred about 13 Ma.

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GSA Memoirs

Basin and Range Extensional Tectonics Near the Latitude of Las Vegas, Nevada

Brian P. Wernicke
Brian P. Wernicke
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Geological Society of America
Volume
176
ISBN print:
9780813711768
Publication date:
January 01, 1990

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