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Plutonic 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
The basic QAPF classification system for plutonic rocks, depicted in Figure 6.12, works well for felsic and intermediate quartzofeldspathic rocks but not well for mafic rocks that contain plagioclase and very little quartz or alkali feldspar (and so plot near the P corner). These plagioclase-rich rocks include diorite, gabbro, norite, and anorthosite. So, distinguishing diorite from gabbro, for example, must be based on one or more of the following: (1) plagioclase composition (in diorite, plagioclase is Na-rich; in gabbro, it is Ca-rich), (2) the ferromagnesian minerals present (hornblende or biotite in diorite; clinopyroxene, orthopyroxene, or olivine in gabbro), (3) the generally darker color that gabbro has compared with diorite, or (4) the speckled black-and-white appearance of common diorite. Furthermore, the QAPF system is not applicable to ferromagnesian rocks that contain no feldspar or quartz. Consequently, the IUGS created separate, but still triangular, naming systems for gabbroic rocks, including gabbro, norite, and anorthosite, and for ultramafic rocks (discussed later in the section “Naming Mafic and Ultramafic Rocks”).
Vanadium as a critical material: economic geology with emphasis on market and the main deposit types
Published in Applied Earth Science, 2022
George J. Simandl, Suzanne Paradis
The number, size, thickness, and grade of individual Fe–Ti–V layers vary from one intrusion to another and even within individual intrusions. For example, 16 Fe–Ti–V layers have been identified in the northern limb of the Bushveld complex (Barnes et al. 2004), and up to 26 layers were recognised in the eastern and western limbs of the same intrusion (Cawthorn and Molyneux 1986; Tegner et al. 2006). The oxide layers vary in thickness from few centimetres to >10 metres, some of them consisting almost entirely of vanadiferous titanomagnetite and ilmenite, whereas others contain substantial proportion of silicates (e.g. plagioclase and pyroxene) and anorthosite xenoliths. The Main Magnetite Layer (4th layer from the bottom in the eastern limb) is 1–2 m thick and historically accounted for more than half of the global vanadium yearly production (Crowson 2001). The magnetite layer 21 can reach a thickness of 60 m but is generally in the order of 10 m in thickness (Maier et al. 2013).
Geochemical systematics and U–Pb zircon age of the Vulvara anorthosite massif, Lapland granulite belt, Baltic shield: magmatic sources and metamorphic alteration of the rocks
Published in Applied Earth Science, 2021
Lyudmila I. Nerovich, Tatiana V. Kaulina, Evgeniy L. Kunakkuzin, Maria A. Gannibal
Anorthosite magmatism is characteristic of the Precambrian evolution of the Earth’s crust. It may provide information about the early stages of the lithosphere evolution. The Lapland Granulite Belt (LGB) is a typical anorthosite occurrence conventionally divided into two branches, southeastern Kandalaksha-Kolvitsa and the western Lapland (Kozlov et al. 1990). LGB displays zoning across the strike of the structures. The southern part of the belt is composed predominantly of garnet amphibolites and mafic granulites, cut across by anorthosite bodies. The central and northern parts are presented predominantly by felsic granulites, alumina gneisses, intermediate granulites, and enderbites (Figure 1). The southern LGB flank was distinguished as an independent formation – Tanaelv Belt – first in the Finnish Lapland (Barbey et al. 1984; Marker 1985), then later on the Russian territory (Balagansky et al. 1998; Glebovitsky 2005). Although some researchers believe that the separation of the Tanaelv belt was unjustified and still consider it as the lower part of the zonally metamorphosed LGB (Kozlov et al. 1990; Mints et al. 1996; Kozlov et al. 2021), the name Tanaelv or Tanaelv-Kolvitsa being used for LGP complex of garnet amphibolites and granulites of the mafic composition is convenient, prevails in foreign papers and being actively introduced into the Russian geological literature (Pozhilenko et al. 2002). According to Glebovitsky (2005), the LGB rocks were formed during the opening and closing of the ocean at the riftogenic, island-arc, subduction, collisional, and postcollisional evolution stages.
Lapland Granulite Belt–Neoarchean subduction zone in the North-Eastern Baltic shield
Published in Applied Earth Science, 2021
N.E. Kozlov, E.V. Martynov, N.O. Sorokhtin
The composition of granulites spans a wide range from essentially felsic to intermediate and mafic, with variation observed along the strike of the belt. The belt is subdivided into two major domains based on the granulite composition. The western domain is dominated by felsic granulites and is distributed through Norway and Finland. Mafic rocks are relatively rare in this area and clustered mainly along the south-western border of the LGB, which also hosts tectonically emplaced anorthosite bodies, such as the Vaskojoki anorthosite complex (Marker 1985; Kozlov 1995a, 1995b). The mafic unit of the western LGB domain is metamorphosed to amphibolite facies and some researchers (Eskola 1952; Barbey et al. 1980; Hörmann et al. 1980; Marker 1985) defined it as separate complex known as the Tana (Tanaelv) belt. The eastern domain, encompassing the granulites distributed mainly in the Russian part of the LGB, exhibits more abundant mafic rocks and anorthosites and relatively less felsic material. The varying composition of the granulites is reflected in lithostratigraphic sections of the belt that systematically change from the north-west to south-east (Figure 1).