PROGRESS TOWARDS COMPLETED MAPPING OF THE SPRINGERVILLE VOLCANIC FIELD, EAST-CENTRAL ARIZONA

The Springerville Volcanic field encompasses a 3000 sq km region situated on the southern margin of the Colorado Plateau in east-central Arizona. The field consists of over 400 cinder cones and their associated, mostly basaltic, flows, ranging from late Pliocene to Pleistocene in age. Forty-five square kilometers of the previously unmapped south-central region of the field were investigated during the 2010 field season. Results of this mapping, combined with previous work, suggest that this region contains flows younger than 0.5 Ma, making this region the youngest yet mapped. Four general flow types characterize these lavas. The first type is identified by varying amounts of olivine phenocrysts, from 2% up to 20% in some picrites. A second flow type contains both olivine and pyroxene phenocrysts, ranging between 2 and 10%. The third type is mostly aphyric, with a plagioclase rich groundmass, suggesting a relatively high silica content. The final type, which is believed to be the most highly evolved set of flows in the field, is characterized by abundant plagioclase feldspar phenocrysts. Four flows of this fourth flow type contain abundant quartz crystals, sometimes up to five centimeters in diameter. A comparison of these lithologies with similar but scattered lavas elsewhere in the field suggests this is the most concentrated set of highly evolved vents in the field. The volumetric ratio of evolved to unevolved flows in the newly mapped area is much higher than that of any other region of the Springerville field, as estimated from aerial extent. Topography in the region is correlated with age, and these evolved flows encompass the highest topographic region of the field. The hypothesis that the south-central portion of the field is the youngest section is also corroborated by correlating the flow extent and character with the basalt stratigraphy found in previously mapped parts of the field.

Geochemistry will be used in the characterization of all of the new flows. Ongoing analysis includes mineral chemistry, with particular focus on the petrogenesis of the more evolved rocks. Work including Ar-Ar dates and paleomagnetic sampling will help refine these age relationships. New data will be used to update the Dynamic Digital Map of the Springerville Volcanic Field (http://ddm.geo.umass.edu/ddm-svf/).