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Date Permissions Signed
Date of Award
Master of Science (MS)
Beck, Myrl E.
Ross, Charles A., 1933-
Pevear, David R.
Paleomagnetic results have been obtained from twenty-five sites in intrusive and extrusive units of Oligocene age from the Platoro caldera, southwestern Colorado, All specimens from each site were subjected to af demagnetization, and the reliability of each site thereby determined. Eighteen sites gave reliable results. Because six sites from the La Jara Canyon tuff appear to have become magnetized during the same small interval of geologic time, their results were combined and their mean pole and direction used in the final calculations. The thirteen remaining reliable sites yielded a paleomagnetic pole at 84.5°N and 306.5°E (o< = 12.9°, k = 11.2). Site-mean directions have an angular standard deviation of 18°, which is considerably greater than the dispersion predicted by models based on the present geomagnetic field but consistent with results from Late Tertiary and Quaternary studies. Because site-mean directions and site poles both have Fisherian distribution, it is not possible to determine whether dipole wobble or random fluctuation caused by a changing non-dipole field could be the cause of the geomagnetic secular variation during the Oligocene; probably both contribute. Interpretations based on mid-Tertiary paleomagnetic poles are consistent with those derived from sea-floor magnetic anomaly patterns, and possibly indicate that some true polar wandering has occurred since the mid-Tertiary, Due to lack of resolution in potassium-argon dating, the polarity time-scale constructed from the Platoro caldera units can only be used as a guide for future paleomagnetic work and geological mapping in the area.
Platoro caldera geology
Western Washington University
San Juan Mountains (Colo. and N.M.)
Copying of this thesis in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Diehl, Jimmy F., "A Paleomagnetic Reconnaissance of the Platoro Caldera, Southeastern San Juan Mountains, Colorado" (1972). WWU Graduate School Collection. 725.