Table S2 - Magma reservoir formation and evolution at a slow-spreading center (Atlantis Bank, Southwest Indian Ridge)

In-situ major element contents (in wt%) of plagioclases (Pl), clinopyroxenes (Cpx) and olivines (Ol) quantified by EPMA at LMV (Clermont-Ferrand, France) and at University of Minnesota (USA). At Clermont-Ferrand, we used a Cameca SX100 equipped with 4 wavelength dispersive X-ray spectrometers (WDS). Analyses were performed with a 15kV accelerating potential and a focused beam using a 15nA beam current. Counting times were of 10 or 20s on peak and also for background. At Minnesota, we used a JEOL JXA-8900 equipped with 4 WDS. Analyses were performed with a 15kV accelerating potential, a beam current of 20nA, and beam diameters of 10 microns for clinopyroxene, 5 microns for plagioclase and 1 micron for olivine. Counting times were of 10s on peak and off peak for all elements. For each mineral and EPMA used, the average 2 sigma error and the counting time (s) per element is indicated at the top of the dataset.