PETROGENETIC INSIGHTS AND VOLCANIC HAZARDS IN THE SPRINGERVILLE VOLCANIC FIELD: A COMPARATIVE STUDY OF BLUE RIDGE MOUNTAIN AND COYOTE HILLS SHIELD VOLCANOES

The Springerville Volcanic Field (SVF) is located on the southern edge of the Colorado Plateau, on the eastern side of Arizona. It is one of the largest volcanic fields in the United States hosting over 450 cinder cones and two distinct polygenetic shield volcanoes, Blue Ridge Mountain and Coyote Hills. These two shield volcanoes are located on the western and eastern extents of the field respectively, and offer insights into the petrogenetic and eruptive history that differs from the dominant monogenetic volcanism of the region. Recent dates suggest that the youngest flows are <50 ka, more recent than previously thought. In addition to the risk this dominantly monogenetic field presents to the surrounding area, a tuff unit recently discovered at the base of Coyote Hills suggests more explosive hazards not previously documented in the field.

The Blue Ridge Mountain volcanic area, located on the western side of the field, has been extensively mapped, revealing 21 distinct volcanic units. These basaltic units are distinguished by variations in mineralogy, texture and flow morphology despite having very similar major and trace element geochemistry. Thin section analyses performed on Blue Ridge Mountain samples found prevalent disequilibrium textures, including sieve-textured and chemically zoned plagioclase, as well as pyroxene reaction rims on xenocrystic quartz. This is indicative of a complex magmatic evolution involving processes such as magma mixing or recharge. A defining feature of the Blue Ridge Mountain lava flows is the abundance of large olivine and plagioclase glomerocrysts, reaching sizes of up to 1 cm. Coyote Hills, the eastern shield volcano, has many parallels with Blue Ridge Mountain. Preliminary mapping and sampling of Coyote Hills has identified glomerocrysts similar in nature to those found at Blue Ridge Mountain highlighting potential shared magmatic processes, though their abundance and distribution remain subjects of ongoing investigation.