Magmatic Mapping of a Shield Volcano

Field mapping techniques on the Blue Ridge Mountain in the Springerville Volcanic Field

Presenter: Christine Anderson

Presenter Status: Undergraduate student

Academic Year: 22-23

Semester: Spring

Department: Geology

Funding Source/Sponsor: Other

Other Funding Source/Program: USGS EDMAP

Abstract:
The Springerville Volcanic Field (SVF) is a well-studied monogenetic volcanic field in eastern-central Arizona on the southern edge of the Colorado Plateau which erupted primarily basaltic magmas between 2.1 and 0.3 Ma. In the summer of 2022 the first mapping of a polygenetic shield volcano on the southwestern edge of the SVF, the Blue Ridge Mountain (BRM), was undertaken to detail its eruptive history. This is significant because the BRM is one of only two polygenetic volcanoes in the SVF. The detailed mapping that had already been done in the region provides a nearly complete eruptive history of approximately 450 monogenetic cinder cones. In order to map the BRM, differences in magmas were determined by walking contacts in the field and studying the lithologies of hand samples to differentiate between the distinct flows. These lithologic variations were later confirmed with geochemical and thin section analysis from the specimens collected in the field to verify the various magma types. A total of 49 samples were collected over an area of 25 km2 revealing 18 unique flows. Preliminary geochemical results reveal primarily subalkaline lava flows, indicative of melts possibly generated at shallow depths. The composition of lavas in the SVF have shown a relative trend from west to east of tholeiitic to alkalic lavas, and initial observations indicate that the majority of vents in the field migrated from west to east with plate motion (Condit et al., 1989). Regional structures then contributed to enhancing the volume and duration of eruptions in some areas of the field (Connor et al., 1992) such as the BRM. A digital map of this shield volcano was created detailing the different magma flows identified, providing evidence of multiple distinct eruptive events, and this map will be incorporated into the existing Dynamic Digital Map of the SVF. The techniques used for this magmatic mapping are applicable in other settings for mapping basalt flows including extraterrestrial explorations. The appearance of unique features like glomerocrysts also warrants further study into the complexities of magma mixing.