EVIDENCE OF REGIONAL STRUCTURAL CONTROLS ON VENT DISTRIBUTION - SPRINGERVILLE VOLCANIC FIELD, ARIZONA

Quantitative analysis of the geographic distribution of vents and comparison with regional structural, petrologic, and vent age data provide insight into the processes governing the emplacement of vents in the Springerville volcanic field, Arizona. A total of 409 vents in the Springerville volcanic field (SVF) have a mean distance to nearest neighbor vents of 955 m, a much closer spacing than is common in some platform-type volcanic fields. Based upon a cluster analysis search radius parameter of 4500 m, these vents comprise seven geographic clusters, with only five outlying vents occurring in the entire field. Cinder cone clusters in the western portion of the field are significantly older than clusters in the eastern portion of the field (p value of <0.001), and there is a tendency for cluster age to decrease to the east. This is Particularly evident when mean cluster ages are calculated for tholeiite, alkaline olivine basalt, and evolved alkaline rock types independently. Application of the two-point azimuth and Hough transform methods demonstrates that regional cinder cone alignments transect these clusters. The most prominent of these alignments trend ENE in the eastern portion of the field and WNW in the western portion of the field, creating an overall arcuate pattern that is subparallel to the trend of the Mogollon Rim and the Colorado Plateau/Transition Zone boundary. These observations suggest that vents (and clusters) migrated from west to east in response to plate motion, but the general pattern of vent migration was complicated by regional structures, which enhanced the volume and duration of magmatism in some areas. The fractures or faults implied by vent alignments indicate that S(hmin) is oriented radial to the Colorado Plateau in the SVF. Preferred vent alignment orientations may be related to extension resulting from plateau uplift, and to a much smaller degree from a minor Basin and Range imprint. While regional in extent, the implied structures appear to differ significantly from some of those in several other plateau-marginal fields in that they cannot be related to major reactivated Precambrian structures. Our vent alignment data differ from those seen by other workers in the Zuni-Bandera and Mount Taylor fields, suggesting the stress field for the SVF is different from other fields in the proposed Jemez lineament. The stress field implied by vent alignment data, combined with structural data, suggests that the southwestern tectonic boundary of the Colorado Plateau of Brumbaugh (1987) should be extended southeastward to include the SVF at the plateau's southern boundary.