Christopher D. Condit

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 Shmin 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 plateaus southern boundary.

Recurrence rates of basaltic volcanism in SP cluster, San Francisco Volcanic Field, Arizona

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Timing of basaltic volcanism along the Mesa Butte Fault in the San Francisco Volcanic Field, Arizona, from 40Ar/39Ar dates: Implications for longevity of cinder cone alignments

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Cross section of a magma conduit system at the margin of the Colorado Plateau

We present crystallization depth vs. temperature estimates for clinopyroxene phenocrysts from the Springerville volcanic field, Arizona. These calculations reveal several intriguing patterns that have considerable implications for magma transport and genesis. First, partial crystallization occurs over a wide depth range (0–60 km), but most partial crystallization occurs between 0 and 30 km. Second, low crystallization temperatures, low-density magmas, and evolved liquid compositions derive exclusively from two depth intervals, 0–12 and 23–30 km. These intervals coincide with a density contrast in the upper crust and a rheology contrast at the base of the middle crust. They also coincide with two highly seismically reflective depth intervals. These relationships indicate that (1) the Moho is not a staging area for volcanic eruptions; (2) density contrasts in the upper crust, and a rheology contrast in the middle crust, control magma transport and liquid evolution; (3) magma conduits are probably magma mush columns, with a preponderance of sills within the 0–12 and 23–30 km intervals; and (4) seismically reflective layers are sills related to Tertiary–Holocene volcanic activity. Moreover, these sills appear to represent the principal sites of magma evolution.

Dynamic Digital Map of the Springerville Volcanic Field and the DDM-Template: An example of an open-source tool to distribute maps, data, articles, and multi-media materials

Dynamic Digital Maps (DDMs) are computer programs that manage the display and distribution of high-quality color maps, digital images, movies, analytical data, and explanatory text, including field guides. They do this in a cross-platform format that opens associated files of maps, images, and movies either from a local device (e.g., a hard drive) or from a web source (server). DDMs are intuitive to use, can be easily and quickly searched for sample and image sites and analytical data, and require no additional software such as web browsers or readers to operate. DDMs fill a niche between the extremes in the digital mapping world that range from a simple digital copy of a paper map to the highly linked geographic information system (GIS) product. A DDM enables one to create an integrated study that confines its focus on a specific map, unlike other interfaces. They offer an ideal way to present, for example, premeeting or postmeeting field trips, so they can be pre-run or revisited, enriching the experience. All DDM maps and images can be saved to disk for printing, and data saved to tab-delimited files. DDMs are made using the open-source DDM-Template, written in the cross-platform programming environment Runtime Revolution, as assisted by videos, tutorials, and the DDM-Cookbook. The DDM of the Springerville volcanic field, the example used here to demonstrate these capabilities, was made from this template. The template is highly extensible, and ongoing modifications and updates are available, as are more than 20 other examples of DDMs.