Geochemical Studies of the Battleship Rock Ignimbrite, Valles Caldera, New Mexico

Abstract

Valles Caldera is the third largest active super volcano in the United States. Despite this, it remains a poorly understood volcanic system. Evidence has been presented within the last 5 years that suggests that Valles Caldera’s eruptive products were spread much farther than previously accepted, as far as Canada. Therefore, it is imperative that new work is put forth to thoroughly understand the recent eruptive history of the caldera in order to better inform disaster response and planning efforts in affected regions.

Battleship Rock Ignimbrite from the Valles Caldera has been understudied when compared to its sister units, and this study aims to attempt to remedy this by making it the primary focus. In this study, zircon U-series dating by secondary ion mass spectrometry (SIMS), Crystal Size Distribution (CSD) analysis, mineral chemistry by Electron Microprobe Analysis (EMPA), and thin section petrology are utilized to characterize the Battleship Rock Ignimbrite of the East Fork Member eruptive products. Both zircon xenocrysts and phenocrysts are present in the Battleship Rock Ignimbrite. The crystal size distribution graphs show varied (concave-up, linear, and mixed) curves. In addition to these quantitative lines of evidence, signs of magma mixing events are also preserved in its plagioclase morphology and chemical makeups. The results of this study support that Valles Caldera underwent magma mixing that triggered the recent eruptions at 70 ka to form the Battleship Rock Ignimbrite.