Geology of the Saint-Marcel valley metaophiolites (Northwestern Alps, Italy)

Figures & data

Figure 1. Geographic location and simplified geology of the study area. (a) Outline of northern Italy and neighbouring countries, and location of the Aosta Valley region (white rectangle). (b) Topography of the Aosta Valley region as obtained by LIDAR technique. The location of the mapped area across the Saint-Marcel valley is outlined by the red line. (c) Simplified geologic map of the Saint-Marcel valley.

Figure 2. Examples of the metaophiolites in the Saint-Marcel valley. (a) Garnet-bearing glaucophanites (GL) interlayered with garnet-chloritoid-glaucophane-bearing chlorite-schists (CHL) and minor talcschists. Fontillon outcrop (northern Saint-Marcel valley; long. 7°27′09.36″E, lat. 45°42′32.08 ″N, alt. 1600 m a.s.l.). The S₂ foliation trace is also shown. (b) Mafic eclogite boudins (E) included within glaucophanites of the Fontillon outcrop. The trace of older S₁ foliation within the eclogite boudin is shown in relation to the S₂ foliation. (c) Tight isoclinal folds marked by eclogite (E)/glaucophanite (GL) contact. S₁ and S₂ traces are shown (Fontillon outcrop). (d) Layer of fine-grained pale-grey impure marble (M) bounded by carbonate-rich micaceous quartzite (Mont-Roux outcrop; long. 7°28′04.41″E, lat. 45°41′26.25″N, alt. 2300 m a.s.l.; see also Figure B in the Main Map). (e) Panoramic view of the eastern side of the Saint-Marcel valley dominated by the Pointe-de-Plan-Rue peak (long. 7°28′05.29″E, lat. 45°39′43.59″N, alt. 2882,9 m a.s.l.). An hectometric recumbent fold is marked by the contact between metasediments and metaophiolites (white dashed line; see also Figure D in the Main Map). (f) Example of micaceous quartzite folded within marble (the outcrop is located between the Pointe-de-Plan-Rue peak and the Grand Crète peak, along the eastern side of the Saint-Marcel valley: long. 7°28′19.93″E, lat. 45°39′36.90″N, alt. 2860 m a.s.l.).

Figure 3. Photomicrographs of the Saint-Marcel valley metasedimentary sequence. All samples are from the Mount-Roux section (see Figure B in the map). (a) Impure marble consisting of calcite, polycrystalline quartz, white mica, garnet, zoisite. (b) Manganiferous quartzite consisting of quartz, garnet, tourmaline, white mica, chlorite. (c, d) Carbonate-rich micaceous quartzite consisting of quartz, white mica, garnet, Fe-rich carbonate, clinozoisite alternating with fine-grained pale-grey marble consisting of calcite, polycrystalline quartz, and white mica. (e, f) Calcschist made of carbonate, polycrystalline quartz, white mica, garnet from the micaceous portion of flysch-like calcschists; relict isoclinal fold hinges are visible (Mount-Roux section). Photomicrographs a, b, d, e were made under cross-polarised light; photomicrographs b, c under plane-polarised light. Mineral abbreviations according to Siivola and Schmid (2007).

Siivola, J., & Schmid, R. (2007). List of mineral abbreviation. In D. Fettes & J. Desmonds (Eds.), Metamorphic Rocks. A classification and glossary of terms (pp. 93–110). New York: Cambridge University Press.

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