Crystal origins and magmatic system beneath Ngauruhoe volcano (New Zealand) revealed by plagioclase textures and compositions

A steady-state balance of intrusion and crystallization in the deep crust, and remobilization and entrainment of co-magmatic crystals in newly formed and ascending magmas has produced relatively monotonous batches of basaltic andesite throughout the volcano's life. Trace element zonation (Fe and Mg) in the plagioclase mostly reflects variable diffusive loss through the crystal history, and the patterns in different crystals are highly variable. This, along with uncertainties in estimating trace element partitioning coefficients, highlights the difficulty of reconstructing melt compositions and subterranean residence time in such magmas.