Fig. 8: TiO2 in plagioclase model for the 1968 Fernandina eruption.
From: Cryptic evolved melts beneath monotonous basaltic shield volcanoes in the Galápagos Archipelago
a Plagioclase TiO2 vs. An# in nodule samples from the 1968 Fernandina eruption and lava samples from historic Fernandina eruptions. Crystals are classified according to their textural association (see legend). Crystal compositions from historic Fernandina lavas are from Allan and Simkin28. Characteristic 2σ analytical uncertainty for our plagioclase analyses is shown for TiO2 and is less than the size of a data point for An#. The grey lines show the compositions of crystals calculated to be in equilibrium with the 1968 Fernandina scoria glass28, using the models of Namur et al.67 for An# and Nielsen et al.43 for TiO2 at 1130 °C (the approximate pre-eruptive crystallisation temperature)28. The black lines show the trajectory of plagioclase compositional evolution calculated using Rhyolite-MELTS and the TiO2 partitioning model of Nielsen et al.43 at 50 MPa (solid line), 300 MPa (dashed line) and 500 MPa (dotted line). Plagioclase comes onto the liquidus at 1191, 1207 and 1222 °C in 50, 300 and 500 MPa models, respectively. The plots above show b the physical and c the compositional evolution of the liquid predicted by Rhyolite-MELTS at 500 MPa (the approximate crystallisation pressure at Fernandina)34.
