Plagioclase compositions and maps
Eight thin section samples were analyzed using five wavelength-dispersive X-ray spectrometers (WDS) to obtain precise, quantitative compositional maps. The sample locations are shown in Fig. 2 and are represented by pink circles. Thin sections were coated with an approximately 20 nm thick carbon layer. The maps were produced at the Department of Earth Sciences, ETH Zurich, using a JEOL JXA-8230 Electron Probe Microanalyzer (EPMA) instrument. The applied acceleration voltage was 15 kV with a 100 nA beam current. A pixel size of 15 mm x 15 mm, a dwell time of 35 ms, and a probe diameter of 10 mm was used for samples BC306, BC304, BC11, BC02, DS12, and DS03. For samples HC01 and SMLG, a pixel size of 25 mm x 25 mm, a dwell time of 50 ms, and a probe diameter of 25 mm was used. The resulting scans allow for precise elemental maps of the sections analyzed and the calculation of chemical formulas of phases of interest. Here, we investigate plagioclase due to its prolonged duration on the liquidus and because the composition records changes in the melt with which it is in equilibrium.