1989 Edition

Alpine mafic magma stem

  • T. P. Thayer
Reference work entry

The term alpine mafic magma stem was proposed for a distinctive petrological association of alpine-type peridotite and gabbro with Na-rich quartz diorite, trondhemite, and albite granite, as exemplified by rocks exposed in Canyon Mountain (Thayer, 1963) and near Sparta (Gilluly, 1933) in eastern Oregon. Peridotite and gabbro, which were emplaced together as a solid tectonic block, constitute about 90% of the rocks; the highly sodic siliceous rocks, rich in volatiles and accompanied by extensive albitization, were intruded very soon after tectonic emplacement of the mafic rocks. The postulated magma series is restricted to eugeosynclincal or alpine mountain belts, hence the name; it comprises the plutonic rocks of the ophiolite assemblage. The prototype rocks in eastern Oregon were intruded during Permian to Triassic time, considerably before the Idaho batholith of early Cretaceous age. The rocks of this magma series in general precede intrusion of large dioritic to granitic batholiths...

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  1. Gilluly, J., 1933, Replacement Origin of the Albite Granite near Sparta, Oregon, U.S. Geol. Surv. Prof. Pap. 175-C, 65–81.Google Scholar
  2. Thayer, T. P., 1963, The Canyon Mountain Complex, Oregon, and the Alpine Mafic Magma Stem, U. S. Geol. Surv. Prof. Pap. 475-C, 82–85.Google Scholar
  3. Thayer, T. P., 1978, The Canyon Mountain Complex, Oregon, and some problems of ophiolites, in R. G. Coleman, and W. P. Irwin, eds., North American Ophiolites, Oreg. Dept Geol. Min. Industries Bull. 95, 93–105.Google Scholar

Copyright information

© Van Nostrand Reinhold 1989

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  • T. P. Thayer

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