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.