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Fig. 3 | Geothermal Energy

Fig. 3

From: The characterisation of an exhumed high-temperature paleo-geothermal system on Terre-de-Haut Island (the Les Saintes archipelago, Guadeloupe) in terms of clay minerals and petrophysics

Fig. 3

Examples of dark fresh (a) and yellowish hydrothermally altered (b) samples as found on the outcrops and corresponding thin sections seen by optical microscopy with plane polarized light (a1 and b1) and crossed polarized light (a2 and b2). Sample A corresponds to a clast in a debris flow while B sample was extracted from a fracture. Thin section of fresh sample A shows a rock in which the primary volcanic minerals and texture are preserved. Phenocrysts are euhedral but fractured (see also Fig. 4). Plagioclase (Pl) displays clear twins and clinopyroxene (Cpx) shows its normal birefringence. The groundmass is composed of µm-sized plagioclase microlites. Sample B seen in thin section shows a strongly transformed texture in which volcanic primary minerals cannot be distinguished anymore as they are replaced by newly formed minerals. Extensive crystallization of K-phyllosilicates (K-phy) and quartz (Qz) is observed. Mineral abbreviations (except for ‘K-phy’) according to Whitney and Evans (2010)

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