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Tectonic implications of the age, composition, and orientation of lamprophyre dikes, Navajo volcanic field, Arizona |
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| Authors: | AW Laughlin MJ Aldrich Jr M Shafiqullah J Husler |
| Institution: | 1Los Alamos National Laboratory, Earth and Space Sciences Division, ESS-1, MS D462, Los Alamos, NM 87545U.S.A. 2Department of Geosciences, University of Arizona, Tucson, AZ 85721U.S.A. 3Department of Geology, University of New Mexico, Albuquerque, NM 87131U.S.A. |
| Abstract: | Fifty-one lamprophyre dikes of the Navajo volcanic field are randomly oriented in contrast to dikes of similar age from adjacent tectonic provinces. KAr ages obtained on nine of these dikes indicate that they were emplaced between 28 and 19 m.y. ago. Initiation of dike emplacement was approximately coeval with the initial demarcation of the Colorado Plateau in the mid-Tertiary. Chemical analyses obtained on nine dike samples show a wide range in composition. Silica contents range from 33.6% in a phlogopite katungite to 55.9% in a felsic minette. Two of the samples have Na2O > K2O indicating that sodic volcanism was occurring concurrently with the dominant potassic volcanism.Published results of high-pressure experimental studies of katungite suggest that this magma was derived from K-metasomatised mantle. Because this potassium metasomatism produces a positive volume change, we propose a model that relates uplift of the Colorado Plateau to metasomatism, magma genesis, and dike emplacement. |
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