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Magmatism in the Context of the Present-Day Tectonic Settings
Published in O.A. Bogatikov, R.F. Fursenko, G.V. Lazareva, E.A. Miloradovskaya, A. Ya, R.E. Sorkina, Magmatism and Geodynamics Terrestrial Magmatism Throughout the Earth’s History, 2020
O.A. Bogatikov, V.I. Kovalenko, E.V. Sharkov, V.V. Yarmolyuk
The most interesting case is a collision of continental plates which occurs within the Alpine–Himalayan Belt. The latter was initiated in the Late Cretaceous–Early Palaeogene by the closure of the Tethys, and its development still continues (Fig. 2.9). At that time, the southern edge of Eurasia was an active margin and the pattern of deep-seated processes was to a large extent inherited by the later collision of continental plates. As a result an extensive Cenozoic andesite–latite volcanic belt was formed, extending across the whole of Eurasia, from the Alboran Sea to the Indonesian–Burma Arc (the Great Andesite Belt of Eurasia: Fig. 2.1) (Milanovsky and Koronovsky, 1974; Borsuk, 1979; Pearce et al., 1990; Arnaud et al., 1992; etc.). It consists of the eastern or Aegian–Caucasus and western or Alpine–Mediterranean segments. Although their structures are of different morphology, they have a number of features in common. Thrust slices, stacked to form an accretionary prism, form arcuate mountain ridges around the periphery. They tend to follow the suture zones of the structures. The thrust sheets often contain fragments of deep-water Tethyan sediments, ophiolitic rocks and locally blocks from the lower crust and even the upper mantle (Milanovsky and Koronovsky, 1974; Chopin, 1987; Quick et al., 1993). The rocks are usually metamorphosed to form schists.
Minerals, rocks, discontinuities and rock mass
Published in Ömer Aydan, Rock Mechanics and Rock Engineering, 2019
Schists are foliated medium-grade metamorphic rock with parallel layers, vertical to the direction of compaction. The schists contain lamellar minerals such as micas, chlorite, talc, hornblende, graphite and others. Quartz often occurs in drawn-out grains to such an extent that a particular form, called quartz schist, is produced. Schist contains more than 50% platy and elongated minerals, often finely interleaved with quartz and feldspar. Schist is characteristically foliated so that individual mineral grains split off easily into flakes or slabs.
Metamorphic Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Figure 10.11 shows a typical schist. Schists are higher- temperature rocks than phyllites, and most form when phyllites are further metamorphosed. Thus, the precursors of schists are shale, slate, and phyllite. Less commonly, however, schist may form by metamorphism of fine-grained igneous rocks, such as tuff or basalt. Large and aligned flaky minerals, easily seen with the naked eye, define schists. These minerals are most commonly muscovite (such as can be seen in Fig. 10.11) or biotite in parallel or near-parallel orientations that give the rocks schistosity—the ability to be broken easily in one direction but not in other directions. Although most schists are mica schists, graphite, talc, chlorite, and hornblende schists are common. Quartz and feldspar are present in mica schists, often deformed or elongated parallel to the micas, and many other minerals are possible. If schists contain prominent porphyroblasts, we name them accordingly. So the schist in Figure 10.6 is a kyanite-staurolite schist, the schist in Figure 10.7 is a garnet schist, and the one in Figure 10.11 would be called a muscovite schist, or simply a mica schist.
Hydrogeological controls on formation of Patearoa saline site in Central Otago, New Zealand and definition of geoecological salt lines
Published in New Zealand Journal of Geology and Geophysics, 2023
Dave Craw, Cathy Rufaut, Stephen Read, Dhana Pillai
Weakly clay-altered schist outcrops are crumbly and form hard but disintegrating surfaces on the terrace scarp and locally on the upper terrace top (Figure 9A,B). Outcrops are surrounded by debris derived by decomposition of these outcrops, and this debris forms highly permeable substrates that consist of cm-scale angular fragments of schist in a matrix of finer grained debris (Figure 8B). The schist is pervasively foliated and segregated on the mm to cm scale into quartz-albite and micaceous (muscovite + chlorite) laminae (Figure 9B). Most of the coarser clasts in the debris (cm scale) are dominated by quartz and albite, with the micaceous debris decomposing into smaller flakes (typically <0.5 mm). Clay alteration products, from albite, muscovite and chlorite, are even finer and locally form a loose cementing matrix to the debris. Rain and wind erosional action removes surficial finer grained debris, leaving an armoured surface of the coarser fragments (Figure 9B). These deposits form irregular areas of bare substrates and associated gravelly substrates with thin (cm scale) proto-soil (Figure 9A–D). The schist debris substrates are typically 5–20 cm thick, although downslope creep causes locally thicker surficial horizons. Similarly, rain and wind redeposition of finer sediments downslope forms thicker accumulations of sandy silt, especially in gullies in the terrace scarp, and on the lower slopes of the terrace scarp near to the salt line (Figure 3A,B; Figure 4B; Figure 9A).
Compositional characteristics of mineralised and unmineralised gneisses and schist around the Abansuoso area, southwestern Ghana
Published in Applied Earth Science, 2023
Raymond Webrah Kazapoe, Olugbenga Okunlola, Emmanuel Arhin, Olusegun Olisa, Daniel Kwayisi, Elikplim Abla Dzikunoo, Ebenezer Ebo Yahans Amuah
The schist is surrounded by the gneisses and appear weathered across the area. The schists are of three types: the carbonate-sericite, sericite-quartz, and biotite-quartz schist. The carbonate-sericite schist is medium-grained and weakly foliated. It is composed of quartz, plagioclase, sericite, and carbonate (calcite) (Figure 2(d)). The calcite is very coarse in the veins and also has few impregnations. Quartz is recrystallised grains, maybe associated with the carbonate or as impregnations. The sericite-quartz schist is medium-grained and composed mainly of sericite, and quartz (Figure 2(e)). Fine to medium-grained texture and strong foliation characterise the biotite-quartz schist (Figure 2(f)). This rock is dominantly composed of quartz and biotite together with minor feldspar. Rare occurrence of disseminated cubic sulphide minerals can be observed in the rocks. The rock is cut by quartz vein composed of coarse-grained quartz mineral.
Brick production and characterization containing coal mining waste
Published in International Journal of Coal Preparation and Utilization, 2023
Gulfem Binal, Aysun Bacaksizoglu
The stony parts found in the coal seam or in the intercut are generally referred to as schistose parts and are abundant in coal mining wastes. Schists are secondary rocks that are recrystallized under shear force and pressure, consisting of plates that can be easily separated from each other in the form of leaves thanks to their thin, parallel, layered structure. Schists are usually formed by the metamorphism of clays and marls (Etimaden 2021).