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Igneous Rocks
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Granitic rocks in which the plagioclase content is greater than that of the potash-feldspar are called granodiorites; their dark minerals (biotite, hornblende) are usually rather more plentiful than in granite, and the amount of quartz is less. As shown in Fig. 5.17 (p. 100), granodiorite is transitional between granite and diorite; its texture is normally coarse-grained. The name tonalite (after the Tonali Pass, Italy) is used for similar rocks in which the plagioclase content is more than two-thirds of the total feldspar; and adamellite (after Mt Adamello) for those in which the potash-feldspar and plagioclase are nearly equal in amount.
3D simulation procedure for compressive strength testing of anisotropic hard rock
Published in Heinz Konietzky, Numerical Modeling in Micromechanics via Particle Methods, 2017
Tonalite is a synonym for quartz diorite, a group of plutonic rocks having the composition of diorite but which contain a noticeable amount of quartz. The term gneissic describes the texture or structure typical of gneisses, with foliation that is more-widely-spaced, less marked, and often more discontinuous than that of rocks of a schistose texture. (Bates and Jackson 1990.)
Petrology, geochemistry and a probable late Cambrian age for harzburgites of the Coolac Serpentinite, New South Wales, Australia
Published in Australian Journal of Earth Sciences, 2018
Defant and Drummond (1990) named intermediate rocks with similar, distinctive chemistry to the Edwardstown Tonalite, adakites. They assigned a specific environment of formation restricted to direct slab melting of hot, young (<25 My) subducted oceanic crust. However, other workers (Atherton & Petford, 1993; Hou, Gao, Qu, Rui, & Mo, 2004; Muir et al., 1995; Tang et al., 2017) have shown that adakites can also form via crustal melting beneath thickened oceanic crust or mafic underplating. Arc or arc-like magmatism is not known from the eastern Lachlan Orogen until at least 10–15 million years later in the Early Ordovician (Percival & Glen, 2007), thus a mafic lower crustal melting model is preferred for the genesis of the Edwardstown Tonalite. In this scenario, the tonalite is most likely derived from the fusion of thickened, altered oceanic crust (garnet amphibolite ± sediments). One likely candidate available for melting is the oceanic crust associated with the lherzolitic protolith of the nearby Coolac Serpentinite.