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Geology
Published in Ronald C. Chaney, Marine Geology and Geotechnology of the South China Sea and Taiwan Strait, 2020
The east–west profile of Taiwan Island as shown in Figure 2.13b consists of a coastal range composed of Miocene andesites and younger sedimentary rocks. Andesite is a gray volcanic rock of intermediate composition between basalt and rhyolite. The coastal range is a former island arc that can be linked to active andesitic islands off the south-eastern coast of Taiwan. Next along the east–west profile is the “long valley (longitudinal valley),” which is a prominent geomorphic feature. Further to the west in the central range are Pliocene clastics and Quaternary molasses. Holocene sediments cover the western Coastal Plain and foothills. In the north-south profile young andesitic volcanoes are found in the extreme north of the island. In addition, in the Miocene-Pliocene coarse-grained sandstone clastics is often found along with coal above North 23 latitude while rocks of the same age in the south are fine-grained and contain little coal, Wu and Chingchang (1991).
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 andesite assemblage consists of rocks varying in their silica content (50–70 wt.%), their alkali content and especially their K2O content. More acid varieties are common in the Central Andes, being dominated by quartz latites, quartz latite–andesites, dacites, rhyodacites and scarce andesites. The southern Andes is a true andesite province, where andesites make up volcanic fields and volcanoes. It should be noted that petrochemically, the rocks may be assigned to two series, i.e. calc-alkaline (MgO-poor high alumina basalts, andesitic basalts and andesites) and shoshonite–latites (shoshonites, latites and quartz latites) series. The most common are rocks of the calc-alkaline series, which make up the main volcanic regions, while rocks of the shoshonite–latite series occur in the easternmost parts of the volcanic region. The SiO2 content varies from 50 to 64 wt.% and the K, Sr, Ba, incompatible element and LREE content is higher than those of the calc-alkaline series.
The use of Calcium Aluminate Cement in shotcrete
Published in Erik Stefan Bernard, Shotcrete: More Engineering Developments, 2004
Ongoing testing and practical experience gained in the field suggested evolutions of the above mix designs to obtain better performing and more user friendly products. For example, corundum-sillimanite is no longer used as an aggregate in abrasion and impact resistance concretes. Although harder than Andesite, it is brittle in nature and crushing of this aggregate resulted in unfavourable fracture that weakened the aggregate as a whole. Andesite has been found to be the most suitable aggregate for use in abrasion and impact resistance concretes to date.
The geological history and hazards of a long-lived stratovolcano, Mt. Taranaki, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2021
Shane J. Cronin, Anke V. Zernack, Ingrid A. Ukstins, Michael B. Turner, Rafael Torres-Orozco, Robert B. Stewart, Ian E. M. Smith, Jonathan N. Procter, Richard Price, Thomas Platz, Michael Petterson, Vince E. Neall, Garry S. McDonald, Geoffrey A. Lerner, Magret Damaschcke, Mark S. Bebbington
Basalts contain phenocrysts of plagioclase, clinopyroxene, titanomagnetite and olivine in a groundmass of brown, cryptocrystalline glass with microcrystalline plagioclase, clinopyroxene and titanomagnetite ± olivine ± orthopyroxene. Apatite is a common accessory phase and hornblende and orthopyroxene are minor constituents, with phlogopite very rare (Gow 1968; Neall et al. 1986; Stewart et al. 1996; Zernack et al. 2012). Basaltic andesites are petrographically similar to the basalts but span two end memberw from pyroxene-basaltic andesites to amphibole-basaltic andesites (the latter containing up to 30% amphibole). The andesites are dominated by plagioclase and amphibole with <20% of samples containing significant modal clinopyroxene. Higher-silica andesites, (e.g. the summit dome) also contain biotite in a groundmass of cryptocrystalline (<0.05 mm), plagioclase, pyroxene and titanomagnetite.
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).
Shallow reworking of magmatic zircon grains of latest Neoproterozoic (Timanian) age in serpentinite of the Voykar Massif, Polar Urals: new constraints from U-Pb isotopic data, and first trace elements and Lu-Hf isotopic data
Published in GFF, 2019
Nikola Koglin, Solveig Estrada, Axel Gerdes
The serpentinite sample RUE 44 was collected on the right, southern bank of the Lagortayu River (66° 25ʹ 53.1ʹ N; 63° 54ʹ 41.8ʹ E) from the lowest part of the outcrop (Fig. 2). Here, the serpentinite is associated with igneous rocks of the mafic complex: several varieties of basalt and a ~5 m large fragment of porphyritic, fluidal textured andesite, probably a dyke (see Supplementary Fig. 1a). The rocks are deformed and tectonically kneaded. Dense, porphyritic and coarser-grained, aphyric basalt varieties are juxtaposed. At its western side, the andesitic fragment is sheared showing a schistose appearance. Basalt and andesite are greenschist-facies metamorphosed. The basalt consists mainly of plagioclase and hornblende, as well as minor to accessory chlorite, titanite-leucoxene-magnetite aggregates, clinozoisite and apatite. The andesite (sample RUE 42; Estrada et al. 2012) has a matrix of plagioclase, alkali feldspar, and hornblende with minor epidote, biotite, chlorite, and accessory apatite. Phenocrysts are plagioclase and hornblende with relic clinopyroxene.