MINIMIZING UNCERTAINTY IN ZIRCON AND PLAGIOCLASE AGE DATING FROM DETAILED PETROGRAPHY

Volcanic minerals offer insight into the mechanism of physical emplacement during, and prior to eruption. This project examines two prominent eruptions, the Oruanui and Taupo eruptions. These eruptions occurred in the caldera forming region of the Taupo Volcanic Zone (TVZ). This region is located on the north island of New Zealand. The Oruanui eruption occurred 26.5ka and was the last super eruption to have occurred on earth. The Taupo eruption happened 1800 year ago. Tephra from each eruption show commonalities in plagioclase feldspar textures. Grains of plagioclase feldspar, host a variety of inclusions and chemical impurities, in each sample. These inclusions have the ability to obscure radiometric dates and resulting calculations of eruption time scales. A wide variety of inclusions were found and identified in this study. In the sample collected from the Taupo eruption: clinopyroxenes, apatites, oxides and glass inclusions were found in grains of plagioclase feldspar. The Oruanui sample had all of the same inclusions, as well as zircon inclusions. This project sets the foundation for the removal of chemical impurities in plagioclase feldspars. This removal is important for constraining geochronology and quantifying thermal conditions of caldera forming eruptions in the future. The mineralogy of these volcanic tephra, reveal the history of specific magmatic reservoirs. The patterns of mineral occurrence may offer insight into magmatic conditions prior to eruption. Overall this project will help minimize age uncertainty for caldera forming magmatic material.