are shield volcanoes mafic or felsic?
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Composite cones are built of felsic to intermediate lava and shield volcanoes of mafic lava. Cinder cones are made of small fragments of a variety of compositions usually from a single eruption.
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Mauna Kea is considered to be a dormant shield volcano in what is commonly known as the "post-shield" stage. Submarine eruptions began to build Mauna kea from the sea floor around ~0.8 million years ago. The basaltic shield stage of volcanism began by at least 0.3 million years ago.
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The Maria are mostly composed of dark basalts, which form from rapid cooling of molten rock from massive lava flows. The Highlands rocks are largely Anorthosite, which is a kind of igneous rock that forms when lava cools more slowly than in the case of basalts.
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['Composite or Strato-volcanoes: A composite volcano is also known as strato-volcano because composite strata or layered structure is formed due to the eruptive material. ... ', 'Where are composite volcanoes located? ... ', 'Shield volcanoes: ... ', 'Cinder cones: ... ', 'Spatter cones: ... ', 'Complex volcanoes: ... ', 'Other Volcanoes.']
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Most volcanoes form at the boundaries of Earth's tectonic plates. These plates are huge slabs of the Earth's crust and upper mantle, which fit together like pieces of a puzzle. These plates are not fixed, but are constantly moving at a very slow rate. They move only a few centimeters per year.
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Igneous rocks may be simply classified according to their chemical/mineral composition as felsic, intermediate, mafic, and ultramafic, and by texture or grain size: intrusive rocks are course grained (all crystals are visible to the naked eye) while extrusive rocks may be fine-grained (microscopic crystals) or glass ( ...
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Mafic magmas are low in silica and contain more dark, magnesium and iron rich mafic minerals, such as olivine and pyroxene. Felsic magmas are higher in silica and contain lighter colored minerals such as quartz and orthoclase feldspar.
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Volcanoes erupt when molten rock called magma rises to the surface. Magma is formed when the earth's mantle melts. Melting may happen where tectonic plates are pulling apart or where one plate is pushed down under another. Magma is lighter than rock so rises towards the Earth's surface.
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Principal Types of Volcanoes. Geologists generally group volcanoes into four main kinds--cinder cones, composite volcanoes, shield volcanoes, and lava domes.
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Igneous rocks form when molten rock cools and becomes solid. Molten rock is called magma when it is below the Earth's surface and lava when it is above. ... Igneous rocks that form below the Earth's surface are called intrusive igneous rocks (or plutonic).
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Composite Volcano. Geologists have identified 3 major types of volcanoes. There's the shield volcano, formed from low viscosity lava that can flow long distances. There are cinder cone volcanoes, which are made by the eruption of lava, ash and rocks that build up around a volcanic vent.
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Shield volcano eruptions are less explosive than composite volcanoes. Cinder cone volcanoes are steep, cone-shaped volcanoes built from lava fragments called 'cinders.
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Igneous rocks form when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust. ... Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet.
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Cinder cone volcanoes are relatively small, rarely exceeding 1,000 feet tall. Composite volcanoes, also known as stratovolcanoes, are towering structures, often rising more than 10,000 feet. Shield volcanoes are broad, typically 20 times wider than they are high. These volcanoes can be massive.
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In geology, felsic is an adjective describing igneous rocks that are relatively rich in elements that form feldspar and quartz. ... Felsic magma or lava is higher in viscosity than mafic magma/lava. Felsic rocks are usually light in color and have specific gravities less than 3. The most common felsic rock is granite.
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Some examples are: Andesite/dacite (extrusive) and diorite/granodiorite (intrusive). Mafic rocks have low silica content (45-55%). They are usually dark-colored and contain iron and magnesium. Some examples are: Basalt (extrusive) and gabbro (intrusive).
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In a widely accepted silica-content classification scheme, rocks with more than 65 percent silica are called felsic; those with between 55 and 65 percent silica are intermediate; those with between 45 and 55 percent silica are mafic; and those with less than 45 percent are ultramafic.