Eocene Through Miocene Volcanism in the Great Basin of the Western United States
New Mexico Bureauof Mines & Mineral Resources Memoir 47, May 1989 91 EXCURSION 3A: Eocene through Miocene volcanism in the Great Basin of the western United States Myron G. Best', Eric H. Christiansen', AlanL. Deino", C. Sherman Gromme", 3 4 Edwin H. McKee , and Donald C. Noble 'Brigham Young University, Provo, Utah 84602; 'Berkeley Geochronology Center, Berkeley, California 94709; 'U.S. Geological Survey, Menlo Park, California 94025; 'University ofNevada, Reno, Nevada 89557 Introduction Geologists of the U.S. Geological Survey, beginning with Cenozoic magmatic rocks in the western United States the Nevada Test Site project in the early and middle 1960's, define a complex space-time-composition pattern that for mapped individual ash-flow sheets over thousands of square many years has posed numerous interpretive challenges. kilometers in the south-central and western Great Basin and One of the more intriguing tectonomagmatic provinces is identified many of their sources. These investigations dem 'the northwestern segment of the Basin and Range province onstrated the feasibility of systematic geologic mapping of in Nevada, western Utah, and minor adjacent parts of Or ash-flow terranes and the utilization of such data for rec egon, Idaho, and California. This segment, characterized ognizing volcanic centers and working out the history of for the most part by internal drainage, is called the Great volcanic fields. Basin (Fig. 1). This paper summarizes characteristics of The magmatic and tectonic development of the Great volcanic rocks in the Great Basin, primarily ash-flow tuff Basin during Cenozoic time was the focus of a number of and subordinate lava, which were.deposited from Eocene papers in the late 1960's and early 1970's based on the body through Miocene time.
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