2. The gabbros were intruded into serpentinized mantle peridotites as irregular bodies tens of metres to kilometres in width, and tens of metres in thickness. Lava cools down very quickly because the surface of the Earth is cold. Explain. And it’s all about location. If magma is thick, gas bubbles cannot easily escape and pressure builds up as the magma … Anorthosite is usually a coarse-grained intrusive igneous rock with color varies between white, yellowish to brown, shades of gray, blush and smoky pigment. Samples of the Manfred Complex near Mount Narryer gave an Sm–Nd whole-rock isochron age of 3680 ± 70 Ma and a Pb–Pb isochron age of 3689 ± 146 Ma (Fletcher et al., 1988). Many anorthosite outcrops are transected by thin veins and stringers of quartz and feldspar, manifesting incipient disaggregation by the granitic protolith to the host quartzofeldspathic gneiss. Anorthosites is typically coarse-grained dark-color rock and composed primarily of plagioclase (labradorite) with minor amount of pyroxene, magnetite and ilmenite ± olivine. Anorthosite can be a source for hosting titanium, aluminum, gemstones, building material and scientific research of similar composition of Moon, Mars, Venus and meteorites. The ferromagnesian minerals are pyroxene (diopside or diallage, augite and hypersthene), hornblende, and olivine, occurring either together or singly. that crystallizes at the surface. Gabbro texture (Figs 4.6(B) and 4.18) is formed by simultaneous long crystallization of bright (leucocratic) and dark ferromagnesian mineral ingredients, so deeply related to each other, that gabbros are extremely solid and tough rocks.Gabbros appear as a densely homogeneous rock often fairly the same texture and composition throughout the rock mass. Cloudflare Ray ID: 60868842da5fed2f (1988), derived by pooling the 207Pb/206Pb ages of a low U-population of largely discordant data from zircons of two anorthosites and a leucogabbro. Gabbros are plutonic rocks formed by cooling and crystallization of molten magma trapped under the Earth’s surface and chemically equivalent to extrusive basalt. FIGURE 4.17. The rock occurs in close association with mafic gabbro and ultramafic layered-intrusive igneous complex, e.g., Bushveld and Stillwater complexes with large platinum group of deposits, and layered igneous complexes with large deposits of chromite at Sukinda and Nausahi (Fig. The core of the boulders is fresh, with a thin skin of bauxite. Massive fine-grained dolerite (dark gray color in the center) intruded in dolostone (buff color on either side) as dyke cutting at steep angle. A thick bed of kaolinite, goethite and some gibbsite underlies the bauxite. 3.8E) and also wide range in V concentration (Fig. Which scientific term names rocks formed from magma? Gabbro can also be gray or light green. In some instances, however, gabbroic rocks return zircon U–Pb ages that are similar to the Dugel Gneiss, implying that differentiated mafic intrusions were emplaced at several stages of the magmatic history of the terrane. Diabase is a subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Composition. Igneous rocks with similar composition are basalt (extrusive equivalent of gabbro) and diabase (the same rock type could be named dolerite or microgabbro instead).. Gabbro with large augite phenocrysts embedded in white plagioclase. Igneous rocks form after cooling and solidifying from magma or lava. The feldspar is chiefly calcic Plagioclase, generally 50–60% Labradorite [(Ca,Na)(Al,Si)4O8], and Plagioclase composition of Bytownite to Anorthite. Pumice is formed from lava that is full of gas. 4.1). Photomicrograph of thin section showing large phenocryst of deformed Plagioclase (Labradorite) in fine-grained Pyroxene and Plagioclase-rich groundmass in massif anorthosite (Haldar and Tišljar, 2014). First, you have to understand the difference between lava and magma. They are closely associated in the field, for example in the Bole River area (Yan, 1979). Albitite intrusions also occur in the peridotites. If igneous rocks are formed by the cooling of magma or lava, how about sedimentary rocks? The gneissic meta-gabbros of Darvel Bay are identical to those samples from the Verma transform fault zone of the equatorial Mid-Atlantic Ridge (Honnorez et al., 1984). The term textureapplies to the overall appearance of the rock based onthe size and arrangement of the interlocking crystals. Extrusive igneous rock, also known as volcanic rock, is formed by the cooling of molten magma on the earth's surface. The rocks are very common in the world. The bauxite ranged from 45–53% A12O3 and contains 64–78 % gibbsite. 3.8A–C). — One is extrusive and one is intrusive. Rhyolite lava flows are very viscous. Igneous Rocks Igneous rocks are formed by the cooling of molten rock. As the magma rises, bubbles of gas form inside it. The lower half of the upper Chenaillet unit (Fig. Figure 2.8. Relict igneous textures are locally preserved, especially plagioclase crystals in anorthosite and orthopyroxene in cumulate-textured pyroxenite, although most rocks have been recrystallized to an equigranular metamorphic texture. Conversely, the lava flows over the surface of the earth. The small quantity of rocks of magmatic origin is indicative of a very slow rate of partial melting in mantle peridotites. Gabbros contain mainly ferromagnesian minerals and plagioclase, the amount of ferromagnesian minerals equaling or exceeding that of the plagioclase. The magma which is inform of molten rock is stored in the earth's crust, i.e below the earth surface, while the lava can be described as a magma, i.e molten rock found on the surface of the earth's crust. Dolerite and diabase rocks are used as crushed stone in road making, concrete mixture in rough masonry, and block paving and ornamental stone in monumental purposes. The main ingredients of dolerite and diabase are mafic lath-shaped plagioclase of about 60% (labradorite and rarely bytownite) set in a finer matrix of clinopyroxene (typically 20–30% augite) and ±olivine (up to 10% in olivine diabase), magnetite and ilmenite (Fig. Anorthosites comprise aggregates of plagioclase megacrysts with sparse, recrystallized intercumulus. According to the plagiogranite suite fine grained having a chilled margin ) exhibits Mg-rich gabbros some. As quartz/coesite Melts ( Yaxley and Brey, 2004 ) rock occurs in some varieties and is serpentinized. 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