Hung et al. (2020) Features of seafloor hydrothermal alteration in metabasalts of MOR origin from the CBC. Supplementary Materials

Supplementary Table 1. Vein orientations from mapping efforts in each field zone. Locations are given as distance east (negative) or west (positive) from the baseline (Fig. 3).<br><br>Supplementary Table 2. Quantitative SEM results for spot epidote chemical analysis organized by sample. The numbers represent the atomic number of each element in the chemical formula of epidote Ca­₂(Fe³⁺,Al)Al₂[SiO₄][Si₂O₇]O(OH).<br>Supplementary Figure 1. Distinguishing structural features from each zone. a) The headland consists of a concentrated zone of vertical veins. b) The headland begins inland with a thrust fault and lava flow. c) Pillows at the pillow island are surrounded by zones of weaknesses where interpillow hyaloclastites have been weathered away. d) Rounded pillows on the horizontal cross-section of pillow island. e) Veins in the deformed zone are compressed compared to those well-preserved at the headland.<br>Supplementary Figure 2. Cataclastic fabrics and textures in sampled pillows are associated with low temperature (250-300^oC) seafloor hydrothermal alteration. For example, reflected light microscopy shows <b>a </b>sulfides in the cataclastic texture of the basalt, <b>b </b>pyrite (yellow), and <b>c </b>sphalerite (red to orange). SEM shows secondary mineral replacement textures such as <b>d </b>an euhedral spear of epidote growth, and <b>e </b>the poikilitic texture of the albitization reaction in plagioclase to produce epidote. Microscopy shows <b>f </b>preserved quartz amydgules in basalt groundmass, <b>g </b>albite twinning in groundmass of plagioclase and pyroxene, <b>h </b>deformed grains with lack of prograde chemical changes, and the lack of carbonates.<br>Supplementary Figure 3. Quantitative SEM data show the compositional variation in the Fe³⁺:Al ratio of epidote samples from the headland (green), pillow island (blue) and the deformed zone (red). Left y-axis show the pistacite number calculated by . Grey line shows the slope governed by the stoichiometry of Fe³⁺ and Al atoms in epidote, which adds up to the sum of three. Green region shows the range for the early pistacitic (Ps=0.28-0.37) epidote variety.