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Figure F11. Photomicrographs of secondary phases and alteration. A, B. Fine-grained basalt with groundmass composed of relatively unaltered plagioclase and pyroxene microcrysts and a glassy mesostasis completely altered to brown anisotropic clay minerals (Thin Section 49; Sample 324(198)-1213B-32R-3, 72–75 cm). C. Glassy mesostasis partially replaced by calcite (Thin Section 48; Sample 324(198)-1213B-31R-3, 73–75 cm). D. Partially altered plagioclase phenocryst. The inner part is relatively fresh, whereas the rim of the phenocryst has been completely replaced, likely by a Na- and/or K-richer feldspar associated with some sericite (Thin Section 52; Sample 324(198)-1213B-33R-6, 106–108 cm). E. Calcite vein showing both blocky and fibrous habits (Thin Section 48; Sample 324(198)-1213B-31R-3, 73–75 cm). A and E are under plane-polarized light; B, C, and D are under cross-polarized light.

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