Felsic intrusive ternary diagram
Igneous rock are geologically important because: Igneous rocks make up approximately ninety five percent of the upper part of the Earth's crust, but their great abundance is hidden on the Earth's surface by a relatively thin but widespread layer of sedimentary and metamorphic rocks.
FELSIC INTRUSIVE TERNARY DIAGRAM SERIES
These are the elements which combine to form the silicate minerals, which account for over ninety percent of all igneous rocks.īowen's reaction series is important for understanding the idealised sequence of fractional crystallisation of a magma. This is because the magma from which the minerals crystallize is rich in only certain elements: silicon, oxygen, aluminium, sodium, potassium, calcium, iron, and magnesium. There are relatively few minerals which are important in the formation of igneous rocks. However, addition of heat from the mantle or from mantle plumes, subduction related compression and burial as well as some rifting, can prompt the continental crust to melt.Īs magma cools, minerals crystallize from the melt at different temperatures ( fractional crystallization). Melting of the continental crust occurs rarely because it is usually dry, and composed of minerals and rocks which are resistant to melting such as pyroxene granulite. Melting begins because of upwelling of hot mantle from deeper portions of the earth, nearer the Planetary core because of water driven off subducted oceanic crust at subduction zones (providing water to lower the melting point of the rocks) and because of decompression caused by rifting. However, most magma is generated at depths of between 20 and 50 km. The mantle is generally over 1000 to 1200 °c beneath the crust, at depths of between 7 and 70km. Melting of rocks requires temperature, water and pressure. Most of the magma which forms igneous rocks is generated within the upper parts of the mantle at temperatures estimated between 600 to 1600 ☌. The mantle, which extends to a depth of nearly 3,000 kilometers is the source of all magma. The crust floats on the asthenospheric mantle, which is convecting due to the forces of plate tectonics. Oceanic crust is composed primarily of basalt, gabbro and peridotite. The continental crust is composed primarily of crystalline basement stable igneous and metamorphic rocks such as granulite, granite and various other intrusive rocks.
The Earth's crust is about 35 kilometers thick under the continents, but averages only some 7-10 kilometers beneath the oceans. The word "igneous" is derived from the Latin ignis, meaning "fire". Over 700 types of igneous rocks have been described, most of them formed beneath the surface of the Earth's crust. This magma can be derived from either the Earth's mantle or pre-existing rocks made molten by extreme temperature and pressure changes. Igneous rocks are formed when molten rock ( magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive ( volcanic) rocks.