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Geologic provinces of the world (USGS)      Shield      Platform      Orogen      Basin      Large igneous province      Extended crust Oceanic crust:      0–20 Ma      20–65 Ma      >65 Ma
Geologic provinces of the world (USGS)
     Shield      Platform      Orogen      Basin      Large igneous province      Extended crust Oceanic crust:      0–20 Ma      20–65 Ma      >65 Ma

Volcanic rock in North America. A geologic or geomorphic province is a spatial entity with common geologic / geomorphic attributes The United States Geological Survey ( USGS) is a scientific agency of the United States government. A shield is generally a large area of exposed Precambrian Crystalline igneous and high-grade metamorphic rocks that form tectonically In geology a platform is a continental area covered by relatively flat or gently tilted mainly Sedimentary strata, which overlie a basement of consolidated Orogeny (Greek for "mountain generating" is the process of natural Mountain building and may be studied as a tectonic structural event as a geographical event and A structural basin is a large-scale structural formation of rock strata formed by tectonic warping of previously flat lying strata. Large Igneous provinces (LIPS were originally defined by Coffin and Eldholm (1992 as areas of Earth's surface that contain very large volumes of magmatic rocks (typically In Geology, a crust is the outermost solid shell of a planet or moon Oceanic crust is the part of Earth's Lithosphere that surfaces in the Ocean basins Annum is one form of the Latin noun meaning Year, not a form normally used for derivatives in modern languages the accusative singular

Plutonic rock in North America.

Igneous rocks (etymology from Latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet Crystallization is the (natural or artificial process of formation of solid Crystals precipitating from a homogeneous --> identical Solution In Geology, an intrusion is a body of Igneous rock that has Crystallized from molten Magma below the surface of the Earth. In Geology, an intrusion is a body of Igneous rock that has Crystallized from molten Magma below the surface of the Earth. Extrusive refers to the mode of Igneous Volcanic rock formation in which hot Magma from inside the Earth flows out (extrudes onto the surface Volcanic rock is an Igneous rock of volcanic origin Texture Volcanic rocks are usually fine-grained or Aphanitic to glassy in This magma can be derived from partial melts of pre-existing rocks in either the Earth's mantle or crust. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided In Geology, a crust is the outermost solid shell of a planet or moon Typically, the melting is caused by one or more of the following processes — an increase in temperature, a decrease in pressure, or a change in composition. Over 700 types of igneous rocks have been described, most of them formed beneath the surface of the Earth's crust. In Geology, a crust is the outermost solid shell of a planet or moon These have diverse properties, depending on their composition and how they were formed.

Contents

Geologic significance

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. Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change

Igneous rocks are geologically important because:

Morphology and setting

In terms of modes of occurrence, igneous rocks can be either intrusive (plutonic), extrusive (volcanic) or hypabbysal. In Geology, an intrusion is a body of Igneous rock that has Crystallized from molten Magma below the surface of the Earth. Extrusive refers to the mode of Igneous Volcanic rock formation in which hot Magma from inside the Earth flows out (extrudes onto the surface Volcanic rock is an Igneous rock of volcanic origin Texture Volcanic rocks are usually fine-grained or Aphanitic to glassy in

Intrusive igneous rocks

Close-up of granite (an intrusive igneous rock) exposed in Chennai, India.
Close-up of granite (an intrusive igneous rock) exposed in Chennai, India.

Intrusive igneous rocks are formed from magma that cools and solidifies within the earth. Surrounded by pre-existing rock (called country rock), the magma cools slowly, and as a result these rocks are coarse grained. The mineral grains in such rocks can generally be identified with the naked eye. Intrusive rocks can also be classified according to the shape and size of the intrusive body and its relation to the other formations into which it intrudes. In Geology, an intrusion is a body of Igneous rock that has Crystallized from molten Magma below the surface of the Earth. Typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes. A batholith (from Greek bathos, depth + lithos, rock is a large emplacement of Igneous intrusive (also called plutonic rock that forms A laccolith is an Igneous intrusion (or concordant Pluton) that has been injected between two layers of Sedimentary rock. In Geology, a sill is a tabular Pluton that has intruded between older layers of Sedimentary rock, beds of Volcanic A dike or dyke in Geology is a type of Sheet intrusion referring to any geologic body that cuts Discordantly ' across planar The extrusive rocks often produce lava flows. Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures

The central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. When exposed by erosion, these cores (called batholiths) may occupy huge areas of the Earth's surface. A batholith (from Greek bathos, depth + lithos, rock is a large emplacement of Igneous intrusive (also called plutonic rock that forms

Coarse grained intrusive igneous rocks which form at depth within the earth are termed as abyssal; intrusive igneous rocks which form near the surface are termed hypabyssal.

Extrusive igneous rocks

Basalt (an extrusive igneous rock in this case); light colored tracks show the direction of lava flow.
Basalt (an extrusive igneous rock in this case); light colored tracks show the direction of lava flow.

Extrusive igneous rocks are formed at the Earth's surface as a result of the partial melting of rocks within the mantle and crust. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided

The melt, with or without suspended crystals and gas bubbles, is called magma. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet Magma rises because it is less dense than the rock from which it was created. When it reaches the surface, magma extruded onto the surface either beneath water or air, is called lava. Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures Eruptions of volcanoes into air are termed subaerial whereas those occurring underneath the ocean are termed submarine. Plate tectonics and hotspots Divergent plate boundaries At the The term subaerial, mainly used in Geology, describes events or structures located at the Earth 's surface "under the air" Black smokers and mid-ocean ridge basalt are examples of submarine volcanic activity. A black smoker or sea vent is a type of Hydrothermal vent found on the Ocean floor. A mid-ocean ridge or mid-oceanic ridge is an underwater Mountain range typically having a valley known as a Rift running along its axis formed by Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock.

The volume of extrusive rock erupted annually by volcanoes varies with plate tectonic setting. Extrusive rock is produced in the following proportions:[1]

Magma which erupts from a volcano behaves according to its viscosity, determined by temperature, composition, and crystal content. In Plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a In Plate tectonics, a convergent boundary – also known as a convergent plate boundary or a destructive plate boundary – is an actively deforming region In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other In Geology, a hotspot is a location on the Earth's surface that has experienced active volcanism for a long period of time Plate tectonics and hotspots Divergent plate boundaries At the Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. High-temperature magma, most of which is basaltic in composition, behaves in a manner similar to thick oil and, as it cools, treacle. Long, thin basalt flows with pahoehoe surfaces are common. Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures Intermediate composition magma such as andesite tends to form cinder cones of intermingled ash, tuff and lava, and may have viscosity similar to thick, cold molasses or even rubber when erupted. For the extinct cephalopod genus see Andesites. Andesite (ˈændəsaɪt is an igneous, Volcanic rock, of intermediate Volcanic ash consists of small Tephra, which are bits of pulverized rock and glass created by volcanic eruptions less than in diameter Tuff (from the Italian "tufo" is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption Molasses or Treacle is a thick Syrup by-product from the processing of the Sugarcane or Sugar beet into Sugar. Felsic magma such as rhyolite is usually erupted at low temperature and is up to 10,000 times as viscous as basalt. This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Volcanoes with rhyolitic magma commonly erupt explosively, and rhyolitic lava flows typically are of limited extent and have steep margins, because the magma is so viscous.

Felsic and intermediate magmas that erupt often do so violently, with explosions driven by release of dissolved gases — typically water but also carbon dioxide. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Explosively erupted pyroclastic material is called tephra and includes tuff, agglomerate and ignimbrite. Pyroclastic rocks or pyroclastics (derived from the Greek πῦρ, meaning fire and κλαστός, meaning broken are Clastic rocks Tephra is air-fall material produced by a volcanic eruption regardless of composition or fragment size Tuff (from the Italian "tufo" is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption Agglomerates (from the Latin 'agglomerare' meaning 'to form into a ball' are coarse accumulations of large blocks of volcanic material that contain at least Ignimbrite is a Volcanic Pyroclastic rock often of Dacitic or Rhyolitic composition Fine volcanic ash is also erupted and forms ash tuff deposits which can often cover vast areas. Volcanic ash consists of small Tephra, which are bits of pulverized rock and glass created by volcanic eruptions less than in diameter

Because lava cools and crystallizes rapidly, it is fine grained. If the cooling has been so rapid as to prevent the formation of even small crystals after extrusion, the resulting rock may be mostly glass (such as the rock obsidian). Obsidian is a naturally occurring Glass formed as an extrusive Igneous rock. If the cooling of the lava happened slowly, the rocks would be coarse-grained.

Because the minerals are mostly fine-grained, it is much more difficult to distinguish between the different types of extrusive igneous rocks than between different types of intrusive igneous rocks. Generally, the mineral constituents of fine-grained extrusive igneous rocks can only be determined by examination of thin sections of the rock under a microscope, so only an approximate classification can usually be made in the field. In Optical mineralogy and Petrography, a thin section is a Laboratory preparation of a rock, Mineral or Soil sample for The optical microscope, often referred to as the "light microscope" is a type of Microscope which uses Visible light and a system of lenses to

Hypabbysal igneous rocks

Hypabbysal igneous rocks are formed at a depth in between the plutonic and volcanic rocks. In Geology, an intrusion is a body of Igneous rock that has Crystallized from molten Magma below the surface of the Earth. Volcanic rock is an Igneous rock of volcanic origin Texture Volcanic rocks are usually fine-grained or Aphanitic to glassy in

Classification

Igneous rocks are classified according to mode of occurrence, texture, mineralogy, chemical composition, and the geometry of the igneous body.

The classification of the many types of different igneous rocks can provide us with important information about the conditions under which they formed. Two important variables used for the classification of igneous rocks are particle size, which largely depends upon the cooling history, and the mineral composition of the rock. Feldspars, quartz or feldspathoids, olivines, pyroxenes, amphiboles, and micas are all important minerals in the formation of almost all igneous rocks, and they are basic to the classification of these rocks. Feldspar is the name of a group of rock-forming Minerals which make up as much as 60% of the Earth 's crust. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in The feldspathoids are a group of tectosilicate Minerals which resemble Feldspars but have a different structure and much lower Silica content The Mineral olivine (when gem-quality also called Peridot) is a Magnesium Iron silicate with the formula ( Mg The pyroxenes are a group of important rock-forming Silicate minerals found in many Igneous and metamorphic rocks. Amphibole (pronounced amfi-bowl defines an important group of generally dark-colored rock-forming inosilicate Minerals composed of double chain SiO4 The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially All other minerals present are regarded as nonessential in almost all igneous rocks and are called accessory minerals. Types of igneous rocks with other essential minerals are very rare, and these rare rocks include those with essential carbonates. In Chemistry, a carbonate is a salt or Ester of Carbonic acid.

In a simplified classification, igneous rock types are separated on the basis of the type of feldspar present, the presence or absence of quartz, and in rocks with no feldspar or quartz, the type of iron or magnesium minerals present. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Rocks containing quartz (silica in composition) are silica-oversaturated. Rocks with feldspathoids are silica-undersaturated, because feldspathoids cannot coexist in a stable association with quartz. The feldspathoids are a group of tectosilicate Minerals which resemble Feldspars but have a different structure and much lower Silica content

Igneous rocks which have crystals large enough to be seen by the naked eye are called phaneritic; those with crystals too small to be seen are called aphanitic. Generally speaking, phaneritic implies an intrusive origin; aphanitic an extrusive one.

An igneous rock with larger, clearly discernible crystals embedded in a finer-grained matrix is termed porphyry. Porphyry is a variety of Igneous rock consisting of large-grained Crystals such as Feldspar or Quartz, dispersed in a fine-grained Porphyritic texture develops when some of the crystals grow to considerable size before the main mass of the magma crystallizes as finer-grained, uniform material.

Texture

Main article: Rock microstructure

Texture is an important criterion for the naming of volcanic rocks. Rock microstructure includes the texture of a rock and the small scale rock structures The texture of volcanic rocks, including the size, shape, orientation, and distribution of mineral grains and the intergrain relationships, will determine whether the rock is termed a tuff, a pyroclastic lava or a simple lava. Rock microstructure includes the texture of a rock and the small scale rock structures A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific Tuff (from the Italian "tufo" is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption Pyroclastic rocks or pyroclastics (derived from the Greek πῦρ, meaning fire and κλαστός, meaning broken are Clastic rocks Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures

However, the texture is only a subordinate part of classifying volcanic rocks, as most often there needs to be chemical information gleaned from rocks with extremely fine-grained groundmass or from airfall tuffs, which may be formed from volcanic ash. Volcanic ash consists of small Tephra, which are bits of pulverized rock and glass created by volcanic eruptions less than in diameter

Textural criteria are less critical in classifying intrusive rocks where the majority of minerals will be visible to the naked eye or at least using a hand lens, magnifying glass or microscope. Plutonic rocks tend also to be less texturally varied and less prone to gaining structural fabrics. Textural terms can be used to differentiate different intrusive phases of large plutons, for instance porphyritic margins to large intrusive bodies, porphyry stocks and subvolcanic dikes (apophyses). Porphyry is a variety of Igneous rock consisting of large-grained Crystals such as Feldspar or Quartz, dispersed in a fine-grained Porphyry is a variety of Igneous rock consisting of large-grained Crystals such as Feldspar or Quartz, dispersed in a fine-grained A dike or dyke in Geology is a type of Sheet intrusion referring to any geologic body that cuts Discordantly ' across planar Mineralogical classification is used most often to classify plutonic rocks. Chemical classifications are preferred to classify volcanic rocks, with phenocryst species used as a prefix, e. g. "olivine-bearing picrite" or "orthoclase-phyric rhyolite".

Chemical classification

Igneous rocks can be classified according to chemical or mineralogical parameters:

Chemical: total alkali-silica content (TAS diagram) for volcanic rock classification used when modal or mineralogic data is unavailable:

Note: the acid-basic terminology is used more broadly in older (generally British) geological literature. Phonolite is an evolved lava which is considered as forming in shallow Magma chambers Phonolite is an igneous, volcanic ( Extrusive) rock Trachyte is an Igneous, Volcanic rock with an Aphanitic to Porphyritic texture In current literature felsic-mafic roughly substitutes for acid-basic.

Chemical classification also extends to differentiating rocks which are chemically similar according to the TAS diagram, for instance;

An idealized mineralogy (the normative mineralogy) can be calculated from the chemical composition, and the calculation is useful for rocks too fine-grained or too altered for identification of minerals that crystallized from the melt. Ultrapotassic igneous rocks are a class of rare volumetrically minor generally Ultramafic or Mafic silica-depleted Igneous rocks. Normative mineralogy is a geochemical calculation of the whole rock geochemistry of a rock sample which estimates the idealised mineralogy of a rock according to the principles For instance, normative quartz classifies a rock as silica-oversaturated; an example is rhyolite. This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. A normative feldspathoid classifies a rock as silica-undersaturated; an example is nephelinite. The feldspathoids are a group of tectosilicate Minerals which resemble Feldspars but have a different structure and much lower Silica content Nephelinite is a fine-grained or Aphanitic Igneous rock made up almost entirely of Nepheline and Clinopyroxene (variety Augite)

History of classification

In 1902 a group of American petrographers proposed that all existing classifications of igneous rocks should be discarded and replaced by a "quantitative" classification based on chemical analysis. They showed how vague and often unscientific was much of the existing terminology and argued that as the chemical composition of an igneous rock was its most fundamental characteristic it should be elevated to prime position.

Geological occurrence, structure, mineralogical constitution, the hitherto accepted criteria for the discrimination of rock species were relegated to the background. The completed rock analysis is first to be interpreted in terms of the rock-forming minerals which might be expected to be formed when the magma crystallizes, e. g. , quartz feldspars, olivine, akermannite, feldspathoids, magnetite, corundum and so on, and the rocks are divided into groups strictly according to the relative proportion of these minerals to one another. [2] [3]

Mineralogical classification

For volcanic rocks, mineralogy is important in classifying and naming lavas. The most important criterion is the phenocryst species, followed by the groundmass mineralogy. A phenocryst is a relatively large and usually conspicuous Crystal distinctly larger than the grains of the rock groundmass of a Porphyritic Igneous Often, where the groundmass is aphanitic, chemical classification must be used to properly identify a volcanic rock.

Mineralogic contents - felsic versus mafic

For intrusive, plutonic and usually phaneritic igneous rocks where all minerals are visible at least via microscope, the mineralogy is used to classify the rock. Phaneritic is a term usually used to refer to igneous rock grain size. This usually occurs on ternary diagrams, where the relative proportions of three minerals are used to classify the rock. A ternary plot, ternary graph, triangle plot, simplex plot, or de Finetti diagram is a barycentric Plot on three variables

The following table is a simple subdivision of igneous rocks according both to their composition and mode of occurrence.

Composition
Mode of occurrence Felsic Intermediate Mafic Ultramafic
Intrusive Granite Diorite Gabbro Peridotite
Extrusive Rhyolite Andesite Basalt Komatiite
Essential rock forming silicates
Felsic Intermediate Mafic Ultramafic
Coarse Grained Granite Diorite Gabbro Peridotite
Medium Grained Diabase
Fine Grained Rhyolite Andesite Basalt Komatiite

For a more detailed classification see QAPF diagram. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Diorite (ˈdaɪəraɪt is a grey to dark grey intermediate intrusive Igneous rock composed principally of Plagioclase Feldspar (typically Gabbro (ˈɡæbrəʊ is a dark coarse-grained intrusive Igneous rock chemically equivalent to Basalt. A peridotite is a dense coarse-grained Igneous rock, consisting mostly of the minerals Olivine and Pyroxene. This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. For the extinct cephalopod genus see Andesites. Andesite (ˈændəsaɪt is an igneous, Volcanic rock, of intermediate Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Komatiites are Ultramafic mantle-derived Volcanic rocks They have low SiO2 low K2O low Al2O3 and high to extremely high Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Diorite (ˈdaɪəraɪt is a grey to dark grey intermediate intrusive Igneous rock composed principally of Plagioclase Feldspar (typically Gabbro (ˈɡæbrəʊ is a dark coarse-grained intrusive Igneous rock chemically equivalent to Basalt. A peridotite is a dense coarse-grained Igneous rock, consisting mostly of the minerals Olivine and Pyroxene. Diabase (ˈdaɪəbeɪs or Dolerite is a Mafic, Holocrystalline, Igneous rock equivalent to Volcanic Basalt or plutonic This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. For the extinct cephalopod genus see Andesites. Andesite (ˈændəsaɪt is an igneous, Volcanic rock, of intermediate Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Komatiites are Ultramafic mantle-derived Volcanic rocks They have low SiO2 low K2O low Al2O3 and high to extremely high A QAPF diagram is a double triangle Diagram which is used to classify Igneous rocks based on mineralogic composition

Example of classification

Granite is an igneous intrusive rock (crystallized at depth), with felsic composition (rich in silica and predominately quartz plus potassium-rich feldspar plus sodium-rich plagioclase) and phaneritic, subeuhedral texture (minerals are visible to the unaided eye and commonly some of them retain original crystallographic shapes). Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Feldspar is the name of a group of rock-forming Minerals which make up as much as 60% of the Earth 's crust. Plagioclase is a very important series of tectosilicate Minerals within the Feldspar family Euhedral Crystals are those that are well-formed with sharp easily-recognized faces

Magma origination

The Earth's crust averages about 35 kilometers thick under the continents, but averages only some 7-10 kilometers beneath the oceans. The continental crust is the layer of granitic, Sedimentary, and Metamorphic rocks which form the Continents and the areas of shallow seabed Oceanic crust is the part of Earth's Lithosphere that surfaces in the Ocean basins The continental crust is composed primarily of sedimentary rocks resting on crystalline basement formed of a great variety of metamorphic and igneous rocks including granulite and granite. Granulites are fine to medium–grained Metamorphic rocks that have experienced high Temperatures of metamorphism composed mainly of Feldspars sometimes associated Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Oceanic crust is composed primarily of basalt and gabbro. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Gabbro (ˈɡæbrəʊ is a dark coarse-grained intrusive Igneous rock chemically equivalent to Basalt. Both continental and oceanic crust rest on peridotite of the mantle. A peridotite is a dense coarse-grained Igneous rock, consisting mostly of the minerals Olivine and Pyroxene.

Rocks may melt in response to a decrease in pressure, to a change in composition such as an addition of water, to an increase in temperature, or to a combination of these processes.

Other mechanisms, such as melting from impact of a meteorite, are less important today, but impacts during accretion of the Earth led to extensive melting, and the outer several hundred kilometers of our early Earth probably was an ocean of magma. Accretion is a process by which material is added to a Tectonic plate. Impacts of large meteorites in last few hundred million years have been proposed as one mechanism responsible for the extensive basalt magmatism of several large igneous provinces. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Large Igneous provinces (LIPS were originally defined by Coffin and Eldholm (1992 as areas of Earth's surface that contain very large volumes of magmatic rocks (typically

Decompression

Decompression melting which occurs because of a decrease in pressure. The solidus temperatures of most rocks (the temperatures below which they are completely solid) increase with increasing pressure in the absence of water. In Chemistry, Materials science, and Physics, the solidus is a temperature (a line on a Phase diagram) below which a given substance is completely Peridotite at depth in the Earth's mantle may be hotter than its solidus temperature at some shallower level. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided If such rock rises during the convection of solid mantle, it will cool slightly as it expands in an adiabatic process, but the cooling is only about 0. Mantle convection is the slow creeping motion of Earth's rocky mantle in response to perpetual gravitationally unstable variations in its density This article covers adiabatic processes in Thermodynamics. For adiabatic processes in Quantum mechanics, see Adiabatic process (quantum mechanics 3°C per kilometer. Experimental studies of appropriate peridotite samples document that the solidus temperatures increase by 3°C to 4°C per kilometer. A peridotite is a dense coarse-grained Igneous rock, consisting mostly of the minerals Olivine and Pyroxene. If the rock rises far enough, it will begin to melt. Melt droplets can coalesce into larger volumes and be intruded upwards. This process of melting from upward movement of solid mantle is critical in the evolution of the earth.

Decompression melting creates the ocean crust at mid-ocean ridgess. A mid-ocean ridge or mid-oceanic ridge is an underwater Mountain range typically having a valley known as a Rift running along its axis formed by Decompression melting caused by the rise of mantle plumes is responsible for creating ocean islands like the Hawaiian islands. A mantle plume is an upwelling of abnormally hot rock within the Earth's mantle. The Hawaiian Islands, once known as the Sandwich Islands, form an Archipelago of 19 Islands and Atolls numerous smaller Plume-related decompression melting also is the most common explanation for flood basalts and oceanic plateaus (two types of large igneous provinces), although other causes such as melting related to meteorite impact have been proposed for some of these huge volumes of igneous rock. A flood basalt or trap basalt is the result of a giant Volcanic eruption or series of Eruptions that coats large stretches of land or the Ocean floor An oceanic plateau (also submarine plateau) is an undersea Large igneous province, the equivalent of continental Flood basalts such as the Deccan Traps Large Igneous provinces (LIPS were originally defined by Coffin and Eldholm (1992 as areas of Earth's surface that contain very large volumes of magmatic rocks (typically

Effects of water and carbon dioxide

The change of rock composition most responsible for creation of magma is the addition of water. Water lowers the solidus temperature of rocks at a given pressure. In Chemistry, Materials science, and Physics, the solidus is a temperature (a line on a Phase diagram) below which a given substance is completely For example, at a depth of about 100 kilometers, peridotite begins to melt near 800°C in the presence of excess water, but near or above about 1500°C in the absence of water. [4] Water is driven out of the oceanic lithosphere in subduction zones, and it causes melting in the overlying mantle. The lithosphere (IPA, from the Greek λίθος for "rocky" + σφαίρα for "sphere" is the solid outermost shell of a rocky Planet. In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other Hydrous magmas of basalt and andesite composition are produced directly and indirectly as results of dehydration during the subduction process. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. For the extinct cephalopod genus see Andesites. Andesite (ˈændəsaɪt is an igneous, Volcanic rock, of intermediate Such magmas and those derived from them build up island arcs such as those in the Pacific ring of fire. A volcanic arc is a chain of volcanic islands or Mountains formed by Plate tectonics as an oceanic Tectonic plate subducts under These magmas form rocks of the calc-alkaline series, an important part of continental crust. Calc-alkaline and calc-alkalic are equivalent terms applied to groups of Igneous rocks that commonly occur together and that have compositions related by the characteristic The continental crust is the layer of granitic, Sedimentary, and Metamorphic rocks which form the Continents and the areas of shallow seabed

The addition of carbon dioxide is relatively a much less important cause of magma formation than addition of water, but genesis of some silica-undersaturated magmas has been attributed to the dominance of carbon dioxide over water in their mantle source regions. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Normative mineralogy is a geochemical calculation of the whole rock geochemistry of a rock sample which estimates the idealised mineralogy of a rock according to the principles In the presence of carbon dioxide, experiments document that the peridotite solidus temperature decreases by about 200°C in a narrow pressure interval at pressures corresponding to a depth of about 70 km. At greater depths, carbon dioxide can have more effect: at depths to about 200 km, the temperatures of initial melting of a carbonated peridotite composition were determined to be 450°C to 600°C lower than for the same composition with no carbon dioxide. [5] Magmas of rock types such as nephelinite, carbonatite, and kimberlite are among those that may be generated following an influx of carbon dioxide into mantle at depths greater than about 70 km. Nephelinite is a fine-grained or Aphanitic Igneous rock made up almost entirely of Nepheline and Clinopyroxene (variety Augite) Carbonatites (kɑrˈbɒnətaɪt are Intrusive or extrusive Igneous rocks defined by mineralogy that comprises more than 50 volume-% Carbonate Kimberlite is a type of potassic Volcanic rock best known for sometimes containing Diamonds It is named after the town of Kimberley in South Africa

Temperature increase

Increase of temperature is the most typical mechanism for formation of magma within continental crust. Such temperature increases can occur because of the upward intrusion of magma from the mantle. Temperatures can also exceed the solidus of a crustal rock in continental crust thickened by compression at a plate boundary. In Chemistry, Materials science, and Physics, the solidus is a temperature (a line on a Phase diagram) below which a given substance is completely Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere The plate boundary between the Indian and Asian continental masses provides a well-studied example, as the Tibetan Plateau just north of the boundary has crust about 80 kilometers thick, roughly twice the thickness of normal continental crust. The Tibetan Plateau, also known as the Qinghai-Tibetan (Qingzang Plateau is a vast elevated Plateau in Central Asia covering most of the Tibet Autonomous Studies of electrical resistivity deduced from magnetotelluric data have detected a layer that appears to contain silicate melt and that stretches for at least 1000 kilometers within the middle crust along the southern margin of the Tibetan Plateau. Electrical resistivity (also known as specific electrical resistance) is a measure of how strongly a material opposes the flow of Electric current. Magnetotellurics (MT is a natural-source Electromagnetic geophysical method of Imaging structures below the Earth 's surface For the Artificial intelligence Androids of the 1990s Science fiction series Space Above and Beyond, see Silicate (AI [6] Granite and rhyolite are types of igneous rock commonly interpreted as products of melting of continental crust because of increases of temperature. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. Temperature increases also may contribute to the melting of lithosphere dragged down in a subduction zone. The lithosphere (IPA, from the Greek λίθος for "rocky" + σφαίρα for "sphere" is the solid outermost shell of a rocky Planet. In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other

Magma evolution

Main article: Igneous differentiation

Most magmas are only entirely melt for small parts of their histories. Igneous differentiation is an umbrella term for the various processes by which Magmas undergo bulk chemical change during the Partial melting process cooling Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet More typically, they are mixes of melt and crystals, and sometimes also of gas bubbles. Melt, crystals, and bubbles usually have different densities, and so they can separate as magmas evolve.

As magma cools, minerals typically crystallize from the melt at different temperatures (fractional crystallization). A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific Crystallization is the (natural or artificial process of formation of solid Crystals precipitating from a homogeneous --> identical Solution Fractional crystallization is one of the most important geochemical and physical processes operating within the Earth's crust and mantle. As minerals crystallize, the composition of the residual melt typically changes. If crystals separate from melt, then the residual melt will differ in composition from the parent magma. For instance, a magma of gabbroic composition can produce a residual melt of granitic composition if early formed crystals are separated from the magma. Gabbro (ˈɡæbrəʊ is a dark coarse-grained intrusive Igneous rock chemically equivalent to Basalt. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Gabbro may have a liquidus temperature near 1200°C, and derivative granite-composition melt may have a liquidus temperature as low as about 700°C. Gabbro (ˈɡæbrəʊ is a dark coarse-grained intrusive Igneous rock chemically equivalent to Basalt. The liquidus temperature, TL or Tliq is mostly used for Glasses and Alloys It specifies the maximum temperature at which Crystals Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Incompatible elements are concentrated in the last residues of magma during fractional crystallization and in the first melts produced during partial melting: either process can form the magma that crystallizes to pegmatite, a rock type commonly enriched in incompatible elements. Incompatible element is a term used in Petrology and Geochemistry. Pegmatite is a very coarse-grained Igneous rock that has a grain size of 20 mm or more such rocks are referred to as pegmatitic. Bowen's reaction series is important for understanding the idealised sequence of fractional crystallisation of a magma. Within the field of Geology, Bowen's reaction series is the work of the Petrologist, Norman L

Magma composition can be determined by processes other than partial melting and fractional crystallization. For instance, magmas commonly interact with rocks they intrude, both by melting those rocks and by reacting with them. Magmas of different compositions can mix with one another. In rare cases, melts can separate into two immiscible melts of contrasting compositions.

There are relatively few minerals that are important in the formation of common igneous rocks, because the magma from which the minerals crystallize is rich in only certain elements: silicon, oxygen, aluminium, sodium, potassium, calcium, iron, and magnesium. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the WikipediaNaming Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 These are the elements which combine to form the silicate minerals, which account for over ninety percent of all igneous rocks. The silicate minerals make up the largest and most important class of rock-forming Minerals They are classified based on the structure of their silicate Ion group The chemistry of igneous rocks is expressed differently for major and minor elements and for trace elements. Contents of major and minor elements are conventionally expressed as weight percent oxides (e. g. , 51% SiO2, and 1. 50% TiO2). Abundances of trace elements are conventionally expressed as parts per million by weight (e. g. , 420 ppm Ni, and 5. 1 ppm Sm). The term "trace element" typically is used for elements present in most rocks at abundances less than 100 ppm or so, but some trace elements may be present in some rocks at abundances exceeding 1000 ppm. The diversity of rock compositions has been defined by a huge mass of analytical data -- over 230,000 rock analyses can be accessed on the web through a site sponsored by the U. S. National Science Foundation (see the External Link to EarthChem).

Etymology

The word "igneous" is derived from the Latin igneus, meaning "of fire". Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. Volcanic rocks are named after Vulcan, the Roman name for the god of fire. In ancient Roman religion and Hellenic neopaganism, Vulcan is the god of beneficial and hindering fire including the fire of Volcanoes He is also Ancient Rome was a Civilization that grew out of a small agricultural community founded on the Italian Peninsula as early as the 10th century BC
Intrusive rocks are also called plutonic rocks, named after Pluto, the Roman god of the underworld. Pluto was the Roman god of the underworld known in Latin as Tertius the counterpart of the Greek Hades.

See also

Footnotes

  1. ^ Fisher, R. This is a List of Minerals for which there are Wikipedia articles This page is intended as a list of all rock types A Amphibolite Andesite Anorthosite Anthracite Large Igneous provinces (LIPS were originally defined by Coffin and Eldholm (1992 as areas of Earth's surface that contain very large volumes of magmatic rocks (typically V. & Schmincke H. -U. , (1984) Pyroclastic Rocks, Berlin, Springer-Verlag
  2. ^ Cross, W. et al. (1903) Quantitative Classification of Igneous Rocks, Chicago, University of Chicago Press
  3. ^ This article incorporates text from the Encyclopædia Britannica Eleventh Edition article "Petrology", a publication now in the public domain. The Encyclopædia Britannica Eleventh Edition (1910–1911 is a 29-volume reference work that marked the beginning of the Encyclopædia Britannica The public domain is a range of abstract materials &ndash commonly referred to as Intellectual property &ndash which are not owned or controlled by anyone [1]
  4. ^ T. L. Grove, N. Chatterjee, S. W. Parman, and E. Medard, (2006)The influence of H2O on mantle wedge melting. Earth and Planetary Science Letters, v. 249, p. 74-89
  5. ^ R. Dasgupta and M. M. Hirschmann (2007) Effect of variable carbonate concentration on the solidus of mantle peridotite. American Mineralogist, v. 92, p. 370-379
  6. ^ M. J. Unsworth et al. (2005) Crustal rheology of the Himalaya and Southern Tibet inferred from magnetotelluric data. Nature, v. 438, p. 78-81

References

External links

Dictionary

igneous rock

-noun

  1. (geology) one of the major groups of rock that makes up the crust of the Earth; formed by the cooling of molten rock, either below the surface (intrusive) or on the surface (extrusive)
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