Abstract by Patricia Ascanio-Pellon
Do Yellowstone Basalts Have a Wet, Subduction-Zone Signature? Evidence from Plagioclase and Olivine Compositions
Some recent studies have concluded that basalts of the Yellowstone hotspot track were strongly influenced by subduction of the Farallon plate based on high concentrations of water (up to 4 wt. %) found within olivine-hosted melt inclusions in tholeiitic basalts from the Snake River Plain and the Columbia River Plateau.
We test this hypothesis by analyzing plagioclase and olivine compositions in basalt from the Kimama core drilled in the central Snake River Plain. Plagioclase contain cores ranging from An78-61 with a strong mode at An75 whereas olivine cores range from Fo85-63 with a mode at Fo75. Plagioclase An and olivine Fo also plot in the dry, Tholeiitic-Ocean Island section of Beard’s (1986) plagioclase An vs. olivine Fo diagram.
Moreover, Putirka’s plagioclase-melt hygrometer and Water and Langue’s hygrometer calculate <1 wt% to negative water content. Our MELTS calculations with Kimama basalts also show that magmas with over 1.5 wt% water do not crystallize plagioclase and olivine simultaneously. In short, the mineral chemical data shows that YSRP basalts are dry and inconsistent with wet, arc-type magmatism.