USING THE PLAGIOCLASE MELT HYGROMETER FOR CAMP FLOWS; DOES IT HOLD WATER?

Large igneous provinces (LIPs) are voluminous volcanic provinces that emplace 10⁵-10⁷ km³ magma, in the process creating vast flood basalt lavas. LIPs have been connected to multiple mass extinctions due to atmospheric change associated with volatile degassing during LIP volcanism; the Deccan Traps occurred at the same time as the end Cretaceous extinction and the Central Atlantic Magmatic province (CAMP) occurred at the same time as the Triassic-Jurassic extinction. Although water plays a large role in eruptive style, water content of LIP magmas is poorly understood. We collected samples in the CAMP flows in the Hartford basin, including samples from the Holyoke flow, the Buttress dike, and the Talcott flow. Samples have been thin sectioned and analyzed for whole rock major and trace element geochemistry. Albite to anorthite ratios of individual plagioclase crystals will be employed to estimate water contents of CAMP magmas using the hygrometer of Waters and Lange. Data from Hartford basin will be combined with published plagioclase compositional data from Morocco. Results will be compared with published H2O concentrations in melt inclusions from other LIPs. Major uncertainties for the plagioclase hygrometer approach include temperature and pressure of crystallization, albite to anorthite ratio changing from the core to the rim of a plagioclase crystal, and equilibrium melt compositions. Future work will include using the electron microprobe to investigate zoning within the plagioclase grains and investigating water contents at various depths by analyzing samples from flows, dikes and sills.