Fig. 5: Fe-XANES maps of the Havre 2012 pumice suite.

a–f XFM Fe elemental maps (µg*cm⁻²) where white pixels correspond to areas of high Fe-intensity, indicating magnetite microlites and nanolites. White scale bars are all equal to 100 µm and scale bars correspond to the panel below each column (e.g., the scale bar in (a) corresponds to the scale bar in (g)). g–l Corresponding Fe-XANES maps presenting the proportion of magnetite (grey scale) and hematite (red scale) merged into one image. m, n Example Fe-XANES spectra of individual pixels results of linear least squares combination fitting (black solid line) with high proportions of m magnetite and n hematite from within the pink raft pumice Fe-XANES area in 3l. Here we show the spectral contributions from magnetite (yellow solid line), hematite (red solid line), and glass (dashed black line) which combined equal the sum-spectrum data (filled black circles). Residuals in the fit (black dots) are shown with a line at zero intensity to guide the eye. Additional spectra from all samples are shown in Supplementary Fig. S8. o Percentage of Fe as hematite (red) and magnetite (yellow) in each Fe-XANES analysis area. Percentages are calculated by averaging the portion of magnetite and hematite in every pixel of an Fe-XANES area determined by fitting every pixel as shown in (m). The error was calculated as the mean of the normalized sum of the residuals from the linear combination fitting. Samples: a, g white seafloor pumice (same as in Fig.1a, e), b, c, h, i two different white raft pumice samples (b, c are the same white pumice in Fig. 1a, e), d–f, j–l) 3 pink raft pumice samples with different intensities of colouration: d, j tan-brown, e, k orange-pink (Fig. 1c, g), f, l red-pink pumice (Fig. 1d, h).