BASALTIC MAGMATIC MAPPING: A SUGGESTED METHODOLOGY AND RESULTS FROM THE SPRINGERVILLE VOLCANIC FIELD
The style of mapping, termed "magmatic mapping" provides a systematic approach focused around individual magmatic events called units. This technique involvesdelineating contacts between units, completely characterizing the unit, placing them into a stratigraphically controlled temporal framework by combining the Geomagnetic Instability Time Scale of Singer (2016) with radiometric dates, and analyzing the data based on these recognized units.
Results from the SVF provide a comprehensive overview of the lifespan of the field, creating a unique resource for understanding its petrogenetic evolution and as a template for comparing similar volcanic fields, whether they be on Earth or studied by remote sensing on other terrestrial-like bodies. The 3000km2 SVF contains 502 distinct units which are mainly lava flows and cinder cones. Olivine phyric lavas (both 'c' and 'd') are the most abundant lithology types, comprising nearly 34% of the total mapped areal extent of outcrop. Olivine/plagioclase bearing and diktytaxitic units, each make up approximately 15% of the outcrop area. Younger units generally trend towards more evolved lithologies such as aphyric or feldspathic basalts. Similarly, lava geochemistry becomes increasingly alkalic in younger units. Overall, using areal extent as a proxy for volume, the largest geochemical class is tholeiites, followed by transitional basalts, alkali-olivine basalts (AOBs) and hawaiites with lesser amounts of the rest of the more evolved classes. The field progressed from large volumes of tholeiitic basalts erupted early in its lifespan, to an intermediate period dominated by AOBs, with its most recent phase dominated by low-volume more alkalic eruptions, a field-wide trend mimicked locally by seven temporal-vent clusters defined by Condit and Connor (1996). These trends, occurring both field wide, and within local clusters provide some predictability as to the types volcanic hazards inherent in active continental, monogenetic volcanic fields.