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13 An Outstanding Mountain: The Matterhorn 189 Fig. 13.2 Aircraft view towards southeast showing how the Matter- horn is in isolated position, in front of the Monte Rosa massif in the background. The pyramid is surrounded by glaciers that emphasize its isolation. In front of the west face in the shade, the Tiefmattengletscher flows to the left, to join the Zmuttgletscher, in direction of the Zermatt Valley (photo H. Rougier) 13.2 13.2.1 A Long Geological History The African Origin of the Pyramid’s Rocks are well visible in the region of Mt Dolin and Arolla, 13 km to the WNW of the Matterhorn (Fig. 13.1). At the height of the Matterhorn shoulder (Fig. 13.6) only a thin band of Mesozoic calcschists is visible (Bücher et al. 2003). 13.2.2 The Oceanic Origin of the Rocks Forming the Base of the Pyramid The rocks that bear witness to the Tethys Sea form the broad base of the Matterhorn (Figs. 13.4, and 13.5), as do all the rocks in the area between Zermatt and Breuil-Cervinia, passing through the Gornergrat and Breithorn (Bearth 1953; Bücher et al. 2003; Fig. 13.7). The Tethys Sea expanded during the Jurassic and then closed during the Cretaceous (Marthaler 2005). The main witnesses of this ocean are ophiolites (Bearth 1953, 1967): serpentinites, metagabbros and metabasaltes. Pillow lavas can be seen here, the shape of which was preserved despite the eclogitic high-pressure alpine metamorphism. A block with pillow lavas is visible at the entrance to the Zermatt Museum, near the church. The rocks of the Matterhorn date from the Paleozoic (Fig. 13.4). The oldest, probably pre-Carboniferous in age, are those of the darker summit (Fig. 13.6). These are hard and resistant rocks of the Valpelline series (Bücher et al. 2003): kingizitic gneisses accompanied by amphibolites and silicate marbles. The great mass of the pyramid is carved in granodioritic orthogneiss (Arolla series) dated 289 Ma by Bussy et al. (1998). These metagranites are intruded by masses of metagabbros, dated 280 Ma by Monjoie (2004). At that time, during the Permian, all continents were united in the Pangea. At the beginning of the Triassic, the Pangea broke into two mega-continents, Laurasia to the north and Gondwana to the south, separated by the Tethys Sea. The rocks of the southern continental margin of the Tethys Sea, rich in Lias breccias and witnesses of the Tethysian rifting,PDF Image | An Outstanding Mountain The Matterhorn
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