A PETROGENETIC MODEL FOR THE SPRINGERVILLE BASALTS IN EAST-CENTRAL ARIZONA

The Springerville Volcanic Field (SVF), located in east-central Arizona, is arguably one of the best-characterized monogenetic volcanic fields. The field overlies the lithospheric transition zone between the Colorado Plateau and the basing and Range province, encompassing 3000 km². Recent efforts in 2010 and 2011 completed the detailed mapping of the field, creating a comprehensive dataset including the recognition of 450 units, their stratigraphic relations, paleomagnetic data from 257 sites, 575 geochemical samples and radiometric dates from 44 flows. The robust dataset allows for establishment of a petrogenetic model, something few studies have focused on for large intraplate volcanic fields. Trace element modeling suggests 1-20% partial melting of a garnet lzherolite source region. On the basis of isotope systematics, the source region for magmas is determined to be heterogeneous with at least two, or possibly three (Cooper and Hart, 1990), distinct sources that correspond to large-scale mantle reservoirs. Thermobarametric calculations suggest a range of temperatures with the majority falling between 1500°C and 1550°C. Pressure calculations correspond to depths ranging from 75 km to 130 km, suggesting a range of partial melting. This agrees well with the fact that SVF lavas become increasingly alkalic as they young, likely coincident with deeper melting, coupled with increasingly small degrees of partial melting.

Since volatiles are fundamentally important to volcanic eruptions, integrating volatile concentrations into the SVF dataset may be an important piece to understanding the petrogenetic processes and volcanic hazard potential of the field. Fourier Transform Infrared Spectrometry (FTIR) is used to measure water and carbon dioxide concentrations in phenocryst-hosted melt inclusions over the span of eruptive products in the SVF to not only understand the volatile contribution within the field, but to compare with other volcanic depositions to further understand volatiles’ effect on eruption style and subsequent hazard.