Flow banding in basaltic pillow lavas from the Early Archean Hooggenoeg Formation, Barberton Greenstone Belt, South Africa July 2010 Bulletin of Volcanology 72(5):579-592 On the other hand, there are the mafics. Felsic lava Felsic (or silicic) lavas such as rhyolite typically form, lava domes (stratovolcano) and are associated with pyroclastic deposits. Intermediate Magma. Felsic or Sialic Magma. Study 70 Igneous Rocks flashcards from Aleen V. on StudyBlue. The Sherbrooke Domain includes basalts, pyroclastic breccias, and felsic tuffs. But most of it is underwater… Occasionally, slivers of oceanic crust are tectonically emplaced on continents (in convergence zone): ophiolites. 1996) and Ontong Java volcanic plateaux (Shipboard Sci-entific Party 2001). Pillow basalts serve as an indicator that lava was erupted into a body of water. Felsic minerals tend to be white, pink and clear (transparent) in color, and hence these rocks will be a lighter overall color, while mafic minerals tend to be dark black, dark red, or dark green colors, and these mafic rocks will be a darker color, often black. Mafic Magma . A) Pillow basalts B) Basalt mostly formed in lava flows C) Scoria and other vesicular basalt D) Felsic and intermediate lava flows E) None of these are correct. All igneous rocks are formed by crystals that form as the molten material cools. Pillow basalts serve as an indicator that lava was erupted into a body of water. Lava tubes form naturally and readily on both shield and composite volcanoes because flowing mafic lava preferentially cools near its margins, forming solid lava levées that eventually close over the top of the flow. These are the magnesium, iron rocks. The series is composed of alkaline basalts, hawaiites, mugearites, benmoreites, phonolites, and trachytes. Much of the world’s oceanic crust consists of basalt, most of which erupted onto the seafloor to form pillow basalts. Shield volcanoes (Figs. Mafic lavas trap fewer gases. • Rhyolitic lavas: high-viscosity felsic lavas, typically erupted at 800o to 1200o C; cool to form rhyolite. Chemical Elements. Remember that felsic rocks are primarily composed of felspar and silica. Scoriaceous lapillus from Etna, Italy. The mafic volcanic rocks are represented by massive and pillow flows and agglomerates, composed of porphyritic and aphyric basalts and basaltic andesites that are mostly amygdaloidal. Pillow lava is very common on Earth, but difficult to find because almost all of it is on the ocean floor. Pillow basalt can also form when mafic lava erupts on land and flows into a lake or into the ocean. Basalts are less explosive than their intermediate and felsic counterparts because: Mafic lavas erupt at higher temperature. Basaltic flows and thirty-five plugs of felsic alkaline volcanic rocks (phonolites and trachytes) of Mio-Pliocene age are exposed to the north and east of Ngaoundéré (Adamawa, Cameroon). The gabbros and the basalts that we see primarily composed ocean crust. Commonly the intense heat of the hot spot will fractionally melt the lower continental crust composed of granodiorites or plagiogranites. Examples can be found on land usually where former ocean floor is tectonically squeezed between two blocks of continental crust. You will be told if your answer is … Lava rocks, generally dark gray, black or red in color, are classified as mafic rocks and are normally formed from fast-flowing lava with a quick rate of cooling, or solidification. The oldest rocks are exposed in the core of the central anticline, occurring as a lava sequence composed of komatiites and komatiitic basalts, which are overlain by a felsic volcanic-sedimentary formation (Fig. 7, 8), a conspicuous feature of the Ethiopian plateau, are composed predominantly of alkaline basalts, with minor felsic lavas and pyroclastic rocks near their summits (Mohr and Zanettin, 1988; Keiffer et al., 2004). The lava flows alternate with tuffs and tuffites of komatiitic and basaltic composition. An example of high viscosity lava is felsic lava, like rhyolite or dacite. Sea floor pillow basalts on the Juan de Fuca Ridge, a divergent plate boundary located about 150 miles (240 kilometers) west of the Washington-Oregon coast. Blocky lava is composed of larger blocks than aa lava and these blocks have much smoother surface. Types of Lava. 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