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Determination of rock stress by anelastic strain recovery measurement of an oriented core in the Nittsu region of Japan
Published in Katsuhiko Sugawara, Yuzo Obara, Akira Sato, Rock Stress, 2020
W. Lin, T. Hirono, T. Nakamura, K. Yamamoto, K. Matsuki, T. Imamura, Y. Oikawa, M. Takahashi, M. Kwasniewski
A deep well named METI (Ministry of Economy, Trade and Industry) Niitsu well was drilled in Niigata Heiya, Japan. The maximum depth of the well reached 5000 m MD with an inclination of about 20º, and the true vertical depth at the bottom of the well was 4702 m. The outline of the geological structure of the region has been given by Imamura (2003). At this site, the anelastic strain of oriented cores obtained from four depths in the range from about 2400m MD to 4500m MD was measured in six independent directions after the release of the corresponding in-situ stresses. In this paper, the anelastic strain measurement results for a core taken from the deepest location as well as the predicted orientations and magnitudes of three-dimensional principal in-situ stresses will be reported. The core of about 10cm in diameter was taken from a depth of 4544 m MD; the rock material was andesite. Major component minerals were feldspar, quartz, enstatite or hypersthene, and hematite. Dry bulk density of the rock was 2.72 g/cm3, and porosity determined using water saturation method was 0.71%. Compressional wave velocities measured in three directions on a cubic specimen obtained from the depth of 4542m MD, being macroscopically the same as the core used for ASR measurement, ranged from 4.4 km/s to 4.8 km/s, and shear wave velocities were 2.8–3.0 km/s. Although a slight difference between the velocities in different directions was revealed, distinct anisotropy of the texture of the cores could not be macroscopically observed. Poisson’s ratio calculated from compressional and shear wave velocities was equal to 0.20, approximately.
Processes of Sedimentation
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
While free energy indicates the susceptibility of a mineral to chemical reaction, the physical stability of a mineral can be expressed in terms of its resistance to abrasion. The ‘durability’ of a mineral has been experimentally shown to be related to its hardness. The scale of resistance to abrasion, as worked out by Thiel (1945), for example, is as follows (starting with the mineral having least resistance): barite, siderite, fluorite, goethite, enstatite, kyanite, hematite, augite, apatite, hypersthene, rutile, hornblende, zircon, epidote, garnet, staurolite, microcline, tourmaline, quartz.
Magmatism and Geodynamics in the Archaean
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
The rocks are represented by quartz- or hypersthene-normative tholeiites. They differ from komatiitic basalts in their higher TiO2, Al2O3, Na2O, K2O, Ba, Sr, Zr and Y content, their higher Zr/Y and Ti/V ratios and their lower MgO/FeO (< 1) ratio. The TiO2 content in some tholeiitic basalts of the Late Archaean-greenstone belts may reach 1.80–2.12%, as has been established in the Abitibi and Olondo belts, but is usually much lower.
Geotourism and geoparks for sustainable rural development and poverty alleviation: Huanggang Dabieshan UNESCO Global Geopark, China
Published in Australian Journal of Earth Sciences, 2022
The Neoarchean ancient continental nucleus, which is located in Huangtuling village (Figure 2b), is composed of gneiss, including hypersthene, garnet and biotite minerals (Nengzhong & Yuanbao, 2008). The Neoarchean gneiss is a typical granulite-facies rock of the Dabie Group Complex situated in the Dabie orogenic belt (Ma et al., 2000) and consists of plagioclase (25%), quartz (20%), K-feldspar (10%), garnet (15%), hypersthene (15%) and biotite (10%), with minor cordierite and hornblende and accessory zircon, magnetite and ilmenite (Chen et al., 1998; Chen et al., 2006). The Huangtuling hypersthene–garnet–biotite gneiss, with an outcrop of approximately 10 by 4 m, yielded a Neoarchean age of 2814 ± 29 Ma (Jian et al., 1999) similar to the oldest crustal rock group in the Kongling Complex in the Yangtze Craton (Ma et al., 2000). The Huangtuling gneiss has a complex multistage evolution (Jian et al.,1999), suggesting three or four geological events during the early Precambrian evolution of the DBGG. This rock unit is not only highly significant for studies on early crustal evolution (Sun et al., 2008), but also offers reference information about the Yangtze Block as a component of the Paleo-Mesoproterozoic Columbia supercontinent (Nengzhong & Yuanbao, 2008; Rogers & Santosh, 2002, 2003; Zhao et al., 2004, 2005).
The lithogeochemical signatures of hydrothermal alteration in the Waihi epithermal district, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2019
Shaun L.L. Barker, Shawn Hood, Rosie M. Hughes, Shannon Richards
This case study focusses on alteration surrounding several Au–Ag vein deposits in the Waihi area, including the well-known Martha, Favona, and Correnso deposits (Braithwaite and Faure 2002; Simpson and Mauk 2007; Mauk et al. 2013). These deposits are all hosted in the Waipupu Formation, an andesite-dominant formation within the Late Miocene Waiwawa subgroup of the Coromandel Group (Brathwaite and Christie 1996). The andesite consists of a plagioclase-phyric two-pyroxene andesite with minor quartz phenocrysts in the lower section (Braithwaite and Faure 2002; Christie et al. 2007). Informally, within the mine, these are often referred to as the quartz andesite and feldspar andesite. Unaltered andesite contains phenocrysts of plagioclase, augite, hypersthene, minor quartz and local hornblende, with accessory magnetite, apatite and zircon. Rocks occur predominantly as flows, with tuffs and thin carbonaceous lake beds in some parts of the sequence which dip ∼40o to the east, suggesting the sequence has been tilted towards the east (Sporli and Cargill 2011). Thus, the western side of Waihi is inferred to expose rocks from greater paleodepths than rocks to the east. The andesites are unconformably overlain by hornblende dacite to the east (Uretara Formation), and then covered by various ignimbrites of late Pliocene to early Quaternary age (Brathwaite and Christie 1996). The samples analysed are mainly from the lower part of the andesite sequence (Figure 2).
Impact lithologies – a key for reconstruction of rock-forming processes and a geological model of the Popigai crater, northern Siberia
Published in Australian Journal of Earth Sciences, 2019
V.L. Masaitis, O.V. Petrov, M.V. Naumov
Some gneiss inclusions in the impact melt are subjected to pyrometamorphic fusion. Such inclusions are 10–20 cm across and were observed in the cores of thick tagamite sheets that have been recorded at depths from several dozens of metres to 500 m or more from the roof of a tagamite body. Pyrometamorphic glass contributes about 50 vol% to these inclusions. Considering the predominantly quartz–feldspar composition of this glass, these rocks can be referred to as buchite. They have diatectic texture resulting from eutectic fusion at the boundaries of corroded relics of quartz and feldspar grains. These primary minerals commonly bear traces of shock metamorphism, as well as of the subsequent thermal influence of the host impact melt. Pyrometamorphic glass with the buchite inclusions also contains hypersthene microlites, which commonly occur as rims around quartz. Feldspar microlites are mostly represented by andesine or labradorite (An45–55), and anorthoclase. In addition, cordierite and ilmenite occur. At high levels of pyrometamorphic fusion, the buchites disintegrate into separate relic mineral grains and anatectic melt. The latter does not mix with the host impact melt and is localised as small (less than 1 mm) spheroids in tagamite.