Camptonite dikes near Boulder Dam, Arizona

Creators: Campbell, Ian; Schenk, Edward T.

Abstract

Near Boulder Dam occur camptonite dikes of possible Quaternary age characterized by amphibole (kaersutite) phenocrysts of exceptional size and unusual distribution—a distribution which suggests that these phenocrysts have formed essentially in place. Rough calculations suggest that these crystals grew to four-inch size in less than 25 days. Serpen-tinization of olivine, formation and size of amygdules, and growth of amphibole phenocrysts are related to distribution of volatiles in the dike magma. Chemical analyses of the amphibole and of the chilled margin of a dike are presented and discussed.

Additional Information

© 1950 by the Mineralogical Society of America. We first visited this locality in the company of Dr. J. Volney Lewis and Mr. Robert H. Rose of the National Park Service, and it was at their suggestion and with their encouragement that the study of these dikes was undertaken. The late Harry Berman provided helpful discussion of the amphibole analysis. colleagues in the National park service and at the California Institute of Technology have aided us in the field and in the laboratory. we have enjoyed stimulating discussions of the curious features of these dikes with many geologists, among whom may be mentioned Dr. V. P. Gianella, Mr. E. D. McKee, Dr. W. E. Powers, Dr. Heinrich Ries, Dr. A. F. Rogers, Dr. E. D. Wilson, and the late Dr. John E. Wolff. To all these persons we wish to express our thanks for aiding this study, whether tangibly or intangibly. To none of them do we assign any responsibility for the conclusions reached or the hypotheses presented.

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