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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
During shearing, mineral grains can become elongated in one direction, and fractures can develop that give a rock a planar texture. Figure 10.5 shows a rock called mylonite, a highly deformed kind of rock created when fine sheared material recrystallizes, from Norway’s Western Gneiss Region. Directed stress, parallel to the layering in this rock, caused feldspar (white) and biotite (black) grains to become elongated as shearing took place. While this was occurring, metamorphism produced wine-red garnet crystals—a single large one can be seen near the left side of the photo and many small ones are scattered throughout. The 1 euro coin is 2.3 cm across, for scale.
The influence of faults on tunnel excavation and support, Sikfors Hydropower Station, Sweden
Published in Hans Peter Rossmanith, Mechanics of Jointed and Faulted Rock, 2020
The different characteristics indicate a different deformation history of faults of Type I and II. The timing of the history is uncertain. The authors’ suggestion is summarized in Table 3. The difference in the type of deformation at stage 3 is concluded to be due to a difference between the parent rocks. The rock in Type I has, during its transition from gabbro to mylonite, already been subject to ductile deformation or recrystallization and the fabric and the composition of mylonite favourize further ductile deformation. The porphyrite in the Type II fault has an aphanitic or glassy fabric, which makes this rock type more prone to brittle deformation.
Hydropower potential and underground construction risks in Nepal Himalayan region
Published in Bjørn Honningsvåg, Grethe Holm Midttømme, Kjell Repp, Kjetil Arne Vaskinn, Trond Westeren, Hydropower in the New Millennium, 2020
The rock within the area belongs to the Melung augen gneiss schuppe zone. The rocks are mainly augen gneiss, but also layers of more banded gneiss occur. Near the base of Midland thrust the rocks consist of mylonite. The southern part of the tailrace tunnel will be close to this mylonite.
Unravelling the D1 event: evidence for early granite-up, greenstone-down tectonics in the Eastern Goldfields, Western Australia
Published in Australian Journal of Earth Sciences, 2021
S. A. Jones, K. F. Cassidy, B. K. Davis
The Fitzroy Fault is a composite structure, comprising the Fitzroy Mylonite and the relatively younger Fitzroy Shear Zone that overprints it (Davis, 2002). The oldest penetrative fabrics at Kanowna Belle and in surrounding Kanowna area are recorded in pods or lozenges of high-strain Fitzroy Mylonite preserved in later lower strain thrust fabrics that record the local reverse kinematics (Davis ET AL., 2000, 2010). The mylonite comprises a planar fine-grained foliation that dips steeply south and hosts an approximately down-dip stretching lineation. Asymmetric porphyroclasts and S-C relationships indicate that movement was reverse, top-to-the-north (Davis ET AL., 2000). A series of large east–west to northeast-trending F1 folds have developed sub-parallel to the Fitzroy Fault and at a high angle to the regional north-northwest-trending regional S2.
A review of the current state of knowledge on gold mineralisation in Benin Republic, West Africa
Published in Applied Earth Science, 2019
Fatchessin Bruno Adjo, Anthony Temidayo Bolarinwa, Luc Adissin Glodji, Franck Wilfried Nguimatsia Dongmo, Jerry Olugbenga Olajide-Kayode
The alluvial gold occurrences of Sarédarou occur on the left bank of the Sarédarou River. It is an area consisting of mylonite containing quartz, feldspar, biotite and hematite. The mineralisation is associated with quartz zone extending over 2800 m2 where eluvial deposits host gold with grades up to 0.1 g t−1(Kirov et al. 1981; Kriatov et al. 1980, 1995).