GEOLOGIC MAPPING COMPLETED IN THE SPRINGERVILLE VOLCANIC FIELD, EAST-CENTRAL ARIZONA

The final unmapped 94 km² of the Springerville Volcanic Field (SVF) was completed during the summer of 2011, building on a successful 2010 effort. The field comprises an area of over 3000 km², dominated by cinder cones and associated basaltic flows ranging from late Pliocene to Pleistocene in age. The two EDMAP-funded campaigns resulted in the recognition of 52 additional units, bringing the total to 464 in the field.

The 2011 work revealed 12 new flows, as well as 10 new vents, and greatly extended the area of numerous previously mapped units. Covering the largest area in this region is a large, probably composite, olivine, pyroxene phyric unit, that displays variability both small and large spatial scales. Aphyric flows dominate the newly recognized units, and the extent of numerous aphyric units that previously bounded the newly mapped region has been greatly extended. Based on stratigraphy, as well as elevation, this area is presumed to contain some of the youngest flows in the SVF. The lithologies of the newly mapped flows strengthens the suggestion that evolved magmas formed late in the eruptive lifespan of the SVF. Several flows contain an abundance of plagioclase, a mineral that dominates the groundmass in aphyric units, including a diktytaxitic flow and one flow has plagioclase phenocrysts to over 1cm in size. Many of the flows also contain quartz, often ranging to over 1cm in size, and, although this quartz is presumed to be xenocrystic, it’s prevalence in three large units is of interest. Several of the feldspathic-rich lavas also contain hornblende.

To aid in building a comprehensive time framework in which to imbed the stratigraphy, 22 paleomagnetic sites were drilled in 14 flow units, adding to the 15 sites obtained in 2010. The polarities for these flows will be placed in magneto-polarity time scale to further constrain their ages. Because the magneto-stratigraphic relations obtained in 2010 call to question some of the older K-Ar ages, we hope to obtain new ⁴⁰Ar/³⁹Ar ages on carefully chosen units to further quantify age relationships. For the samples collected, chemical analysis will be completed, as was done for the existing 556 samples throughout the field. New data will be input into the Dynamic Digital Map of the Springerville Volcanic Field (http://ddm.geo.umass.edu/ddm-svf/).