Paleomagnetic, anisotropy of magnetic susceptibility, and geochronologic data from the Buena Vista intrusion, north-central New Mexico
M. S. Petronis, G. Castillo, J. Lindline, J. Zebrowski, W. McCarthy, D. Lemen, and W. McIntosh


The Buena Vista intrusion outcrops on the eastern side of the Sangre de Cristo Mountains near the transition between the Rocky Mountains and the Great Plains. Along the five kilometer strike of the intrusion, at least three compositionally distinct phases occur. These include a marginal augite porphyritic basalt, a main-phase hornblende gabbro, and a central plagioclase-rich (tourmaline anorthosite) phase. In order to assess the emplacement mode, along-strike variation in emplacement style and/or deformation, and the absolute age of emplacement, we conducted detailed rock magnetic, paleomagnetic, anisotropy of magnetic susceptibility (AMS), and 40Ar/39Ar age determinations. Rock magnetic experiments reveal that the primary magnetic phase is a cubic, Fe-Ti oxide phase (titanomagnetite) of a pseudosingle domain to multi-domain grain size with low to moderate Ti substitution. Paleomagnetic data from thirteen of the eighteen sites collected yield a dominantly single component reverse polarity magnetization that is clockwise discordant to the mid-Miocene expected direction. AMS data from fifteen of eighteen sites yield remarkably consistent results along strike of the dike, characterized by well-defined oblate susceptibility ellipsoids with magnetic foliation planes that strike parallel to the trend of the dike and K1 magnetic lineations that trend south-southwest with a low plunge (<30°). Four of the five new 40Ar/39Ar age determinations yield generally well-defined plateau or isochron ages that range in age from 14.71 Ma to 14.20 Ma. One sample yields a disturbed age spectra for which we did not assign an age. We postulate that the region east of the Sangre de Cristo range front, at this latitude, experienced a modest amount of clockwise vertical axis rotation and that magma emplacement occurred with flow sub-horizontally from the northnortheast to the south-southwest. The Buena Vista intrusion is part of, until now, a previously unrecognized suite of igneous intrusions that were emplaced during the middle Miocene that we define as the Las Vegas Igneous Province. 


  1. Petronis, M. S.; Castillo, G.; Lindline, J.; Zebrowski, J.; McCarthy, W.; Lemen, D.; McIntosh, W., 2015, Paleomagnetic, anisotropy of magnetic susceptibility, and geochronologic data from the Buena Vista intrusion, north-central New Mexico, in: Geology of the Las Vegas Region, , New Mexico Geological Society, Guidebook, 66th Field Conference, pp. 193-204.

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