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ESM D. Petrographical part. D.1 Petrography

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Fig. D1. Andesitic flows are primarily characterized by a flow banding expressed in particular by arranged and parallel oriented larger phenocrysts (A, B). The phenocrysts mineral suite comprises primarily plagioclase and variable amounts of altered clinopyroxene, late magmatic magnetite, and accessory orthopyroxene and quartz. Hornblende is scarce (H). All phenocrysts vary distinctly in size, locally two different generations can be distinguished. Variably altered hypidiomorphic or fragmental plagioclase crystals are characterized by polysynthetic twinning (C), in contrast to simply twinned sanidine (D). Magmatic clinopyroxene occurs mainly as small prismatic crystals containing exsolved magnetite and ilmenite crystals (E). Where cut parallel to (001) (pseudo-)hexagonal, octagonal or square shapes are displayed, simplifying the ranking of completely altered undefined minerals among these (F). Quartz crystals have anhedral to fragmental shape. Fragments of destroyed quartz veinlets are rare (G). Polished thin sections, transmitted light, crossed polarization filters.

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Fig. D2. The primary magmatic groundmass of flows is rarely preserved. Mostly, only small feldspar laths point to a former microcrystalline groundmass with flow texture (A), or, alternatively, a microcrystalline equigranular groundmass is indicated (B). Rarely, small gabbroic fragments were assimilated. The fragments can have a virtually porphyritic texture (C) or plagioclase and clinopyroxene are closely intergrown (D). Polished thin section, all transmitted light, crossed polarization filters.

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Fig. D3. BSE images of oscillatory zoned plagioclase crystals. Mostly, zonation changes from andesine (dark layers) to labradorite (bright layers; A), but also zonations from oligoclase to bytownite are present (B).

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Fig. D4. Primary magmatic pyroxenes are discriminated as enstatite and diopsitic augite in the ternary Ca-Mg-Fe diagram of Morimoto et al. (1988). Secondary metasomatic pyroxenes belong to the diopside-hedenbergite solid-solution series (EMP analysis).

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Fig.

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Fig. D5. Porphyritic andesites show largely the same petrographic features as andesitic flows, though instead of an alignment, phenocrysts express a pronounced porphyritic (A) or glomeroporphyritic texture (B). The phenocryst mineral suite is almost identical. Special features are subrounded, altered plagioclase crystals (C) and assimilated B-veinlet fragments (D). Crystal tuffs are coarse-grained, distinctly altered porphyritic andesites (E). Andesitic dikes show a clear flow texture with aligned and oriented phenocrysts (F). Ignimbrites are internally layered, porous and non-welded. Subrounded, former gas-vesicles are filled with phyllosilicates (G). Larger crystals are embedded and aligned in an equigranular, fine-grained mainly fragmental matrix (H). Polished thin sections, transmitted light. E: straight polarization filters; A-D, F-H: crossed polarization filters.

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Fig. D6. Litho-crystal tuffs possess subrounded clasts embedded in an igneous, inhomogeneous, pervasively altered matrix. Crystals are largely fragmental. Some tuffs exhibit a large proportion of glomerocrystic plagioclase (A). Subrounded clasts of andesitic porphyry are characteristic of monomictic breccias (B). Magmatic breccias show an igneous matrix. They have assimilated different types of fragments, including those of porphyritic andesites (C). Tuffisite dikes are composed of comminuted material which is frequently aligned in small layers due to fluidization effects (D). Magnetite breccias are pervasively argillic altered breccias with a replacement mineral suite dominated by extremely dark phyllosilicates, occurring particularly within the matrix (E, F). Within matrix, small magnetite and ilmenite crystals occur randomly distributed (G). They are of distinctly minor quantity than in clasts where they show cauliflower resembling textures (H). Polished thin sections. A-D: transmitted light, crossed polarization filters. E, F: transmitted light, straight polarization filters. G, H: reflected light, oil immersion.

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Fig. D7. CL images of quartz-eyes, comprising individual (A-D) and glomerocrystic crystals (E, F). They are characterized by rounded contours and local embayments. The individual crystals have zones of light and darker grey colors indicating an inhomogeneous trace element distribution (A-D). They have bright encompassing fuzzy rims originating from post-depositional overprinting hydrothermal fluids (A-D). Silicification is in addition reflected by the small, bright crystals within the igneous groundmass (A-D, G, H). All quartz-eyes are cut by curved fissures. Some quartz-eyes are characterized by an in part cellular, spherulitic or globular internal texture under CL not attributable to microfissures (E-G). H: The quartz-eye exhibits a dark inner core and a slightly brighter rim, both separated by a clear continuous line. The rim is in part scraggy developed indicating a later corrosion event. The color of the rim contrasts clearly with that of hydrothermal precipitations pointing to a second magmatic crystallization stage. A: The small dark spots result from EMPA analyses. Beam current: 30 nA, acceleration voltage: 15.0 kV; working distance 11 mm.

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D.2 References Morimoto, N., Fabries, J., Ferguson, A.K., Ginzburg, I.V., Ross, R., Seifert, F.A., Zussman, J., Aoki, K., Gottardi, G., 1988. Nomenclature of pyroxenes. American Mineralogist, 73, 1123-1133.