La clasificación de los muchos tipos diferentes de rocas ígneas, puede proveernos de importante información, sobre las condiciones bajo las cuales se formaron. Dos importantes variables, usadas para la clasificación de rocas ígneas, son el tamaño de partícula, que depende de su historia de enfriamiento, y la composición mineral de la roca. Feldespatos, cuarzo, feldespatoides, olivinas, piroxenos, anfíboles y micas son minerales importantes que forman parte de casi todas las rocas ígneas, y son básicos en la clasificación de estas rocas. Los otros minerales presentes, se denominan minerales accesorios. Son muy raras las rocas ígneas con otros minerales esenciales.

Las rocas ígneas se clasifican de acuerdo con su origen, textura, mineralogía, composición química y la geometría del cuerpo ígneo.

Texture

The texture of an igneous rock is used to describe its general appearance based on the size, shape and arrangement of the crystals that compose it. In a simplified scheme, up to six igneous textures can be distinguished:[3]​.

Plutonic rocks usually have phaneritic, porphyritic and pegmatitic textures, while volcanic rocks have a glassy, ​​aphanitic or pyroclastic texture.

Chemical composition

Igneous rocks are mainly composed of silicates (SiO); These two elements, plus the ions aluminum, calcium, sodium, potassium, magnesium and iron constitute approximately 98% by weight of the magmas. When these cool and solidify, these elements combine to form two large groups of silicates:[3]​.

Igneous rocks can be classified, depending on the proportion of light and dark silicates, as follows:

The following table is a simple subdivision of igneous rocks, according to their composition and origin:.

Chemical classification is also extended to differentiate rocks, which are chemically similar, according to the TAS diagram, for example:

Mineralogical composition

The QAPF diagram is a double triangular diagram used to classify igneous rocks according to their mineralogical composition. The acronym QAPF corresponds to "quartz (English: Quartz), alkali feldspar (English: Alkali feldspar), Plagioclase, Feldespathoid", which are the mineral groups used for classification in the QAPF diagram. The percentages of Q, A, P, and F are normalized (recalculated so that their sum is 100%).

El magma se origina de la fusión parcial de rocas preexistentes dentro de la corteza terrestre y el manto superior a profundidades que pueden superar los 250 km.[3]​.

La corteza de tierra alcanza un promedio de cerca de 35 kilómetros de grueso bajo los continentes, pero alcanza solo unos 7-10 kilómetros debajo de los océanos. La corteza continental está compuesta primariamente de rocas sedimentarias que descansan sobre una base cristalina formada de una gran variedad de rocas metamórficas e ígneas, incluyendo granulita y granito. La corteza oceánica está compuesta principalmente por basalto, y gabro. Ambas cortezas, continental y oceánica, descansan sobre la peridotita del manto.

Las rocas pueden derretirse en respuesta a una disminución en la presión, a un cambio en la composición (como una adición de agua) o a un aumento en temperatura. Otros mecanismos, como la fusión por el impacto de un meteorito son mucho menos importantes hoy, durante el crecimiento de la Tierra los innumerables impactos llevaron a la fusión de varios cientos de los kilómetros más externos de nuestra Tierra temprana, cuando fue probablemente un océano del magma. Se ha propuesto que impactos de grandes meteoritos en los últimos cientos millones de años como un mecanismo responsable del amplio magmatismo basáltico de varias grandes provincias ígneas").

Temperature

The increase in temperature is the typical factor that leads to the melting of rocks and the formation of magma. It can occur when a hot igneous body rises and intrudes into the crust whose rocks melt. This usually occurs at the convergent boundaries of tectonic plates, such as the collision of India with the Eurasian plate.[4]​.

Granite and rhyolite are believed to be igneous rocks that form by melting of the continental crust due to rising temperatures. Rising temperatures can also contribute to the melting of sinking lithosphere in a subduction zone.

Decompression

Melting "Melting (change of state)") by decompression occurs due to a decrease in pressure.[5] The melting temperature of most rocks increases, in the absence of water, with increasing pressure, and this increases with depth. Thus, a very hot deep rock can remain solid due to the enormous confining pressure to which it is subjected; If the rock rises and its confining pressure decreases faster than its temperature (rocks are poor conductors of heat), it will melt. This fusion process, in the upward movement of the solid mantle through convection currents, is critical in the dynamics of the Earth. Decompression melting creates new oceanic crust at mid-ocean ridges, creating mantle plumes that have given rise to island chains like Hawaii. Decompression melting is the most common explanation for "Trap (geology)") basaltic floods (trapp) and oceanic plateaus, two types of large igneous provinces.

Effects of water and carbon dioxide

Another important factor that affects the melting temperature of rocks is their content of water and other volatile substances, which cause the rock to melt at temperatures below a given pressure. For example, at a depth of about 100 kilometers, peridotite begins to melt near 800 °C, in the presence of water, but in its absence it melts at about 1500 °C.[6] In subduction zones, as an oceanic plate sinks, the increase in temperature and pressure expels water from the rocks of the subducted crust, which causes the melting of the overlying mantle, giving rise to basaltic magmas and andesitics. These magmas and others derived from them were what built the volcanic island arcs throughout the Pacific Ring of Fire.

The addition of carbon dioxide (CO) is a much less important cause in the formation of magmas, although some of them are believed to form in regions of the mantle where CO predominates over water. At a depth of 70 km, carbon dioxide lowers the melting point of peridotite by 200 °C; at greater depths, the effect may be greater; It is estimated that at 200 km it is reduced between 450 °C and 600 °C. The magmas that give rise to rocks such as nephelinite), carbonatite and kimberlite may be generated by the influx of carbon dioxide into the mantle at depths greater than 70 kilometers.[7]​.

La clasificación de los muchos tipos diferentes de rocas ígneas, puede proveernos de importante información, sobre las condiciones bajo las cuales se formaron. Dos importantes variables, usadas para la clasificación de rocas ígneas, son el tamaño de partícula, que depende de su historia de enfriamiento, y la composición mineral de la roca. Feldespatos, cuarzo, feldespatoides, olivinas, piroxenos, anfíboles y micas son minerales importantes que forman parte de casi todas las rocas ígneas, y son básicos en la clasificación de estas rocas. Los otros minerales presentes, se denominan minerales accesorios. Son muy raras las rocas ígneas con otros minerales esenciales.

Las rocas ígneas se clasifican de acuerdo con su origen, textura, mineralogía, composición química y la geometría del cuerpo ígneo.

Texture

The texture of an igneous rock is used to describe its general appearance based on the size, shape and arrangement of the crystals that compose it. In a simplified scheme, up to six igneous textures can be distinguished:[3]​.

Plutonic rocks usually have phaneritic, porphyritic and pegmatitic textures, while volcanic rocks have a glassy, ​​aphanitic or pyroclastic texture.

Chemical composition

Igneous rocks are mainly composed of silicates (SiO); These two elements, plus the ions aluminum, calcium, sodium, potassium, magnesium and iron constitute approximately 98% by weight of the magmas. When these cool and solidify, these elements combine to form two large groups of silicates:[3]​.

Igneous rocks can be classified, depending on the proportion of light and dark silicates, as follows:

The following table is a simple subdivision of igneous rocks, according to their composition and origin:.

Chemical classification is also extended to differentiate rocks, which are chemically similar, according to the TAS diagram, for example:

Mineralogical composition

The QAPF diagram is a double triangular diagram used to classify igneous rocks according to their mineralogical composition. The acronym QAPF corresponds to "quartz (English: Quartz), alkali feldspar (English: Alkali feldspar), Plagioclase, Feldespathoid", which are the mineral groups used for classification in the QAPF diagram. The percentages of Q, A, P, and F are normalized (recalculated so that their sum is 100%).

El magma se origina de la fusión parcial de rocas preexistentes dentro de la corteza terrestre y el manto superior a profundidades que pueden superar los 250 km.[3]​.

La corteza de tierra alcanza un promedio de cerca de 35 kilómetros de grueso bajo los continentes, pero alcanza solo unos 7-10 kilómetros debajo de los océanos. La corteza continental está compuesta primariamente de rocas sedimentarias que descansan sobre una base cristalina formada de una gran variedad de rocas metamórficas e ígneas, incluyendo granulita y granito. La corteza oceánica está compuesta principalmente por basalto, y gabro. Ambas cortezas, continental y oceánica, descansan sobre la peridotita del manto.

Las rocas pueden derretirse en respuesta a una disminución en la presión, a un cambio en la composición (como una adición de agua) o a un aumento en temperatura. Otros mecanismos, como la fusión por el impacto de un meteorito son mucho menos importantes hoy, durante el crecimiento de la Tierra los innumerables impactos llevaron a la fusión de varios cientos de los kilómetros más externos de nuestra Tierra temprana, cuando fue probablemente un océano del magma. Se ha propuesto que impactos de grandes meteoritos en los últimos cientos millones de años como un mecanismo responsable del amplio magmatismo basáltico de varias grandes provincias ígneas").

Temperature

The increase in temperature is the typical factor that leads to the melting of rocks and the formation of magma. It can occur when a hot igneous body rises and intrudes into the crust whose rocks melt. This usually occurs at the convergent boundaries of tectonic plates, such as the collision of India with the Eurasian plate.[4]​.

Granite and rhyolite are believed to be igneous rocks that form by melting of the continental crust due to rising temperatures. Rising temperatures can also contribute to the melting of sinking lithosphere in a subduction zone.

Decompression

Melting "Melting (change of state)") by decompression occurs due to a decrease in pressure.[5] The melting temperature of most rocks increases, in the absence of water, with increasing pressure, and this increases with depth. Thus, a very hot deep rock can remain solid due to the enormous confining pressure to which it is subjected; If the rock rises and its confining pressure decreases faster than its temperature (rocks are poor conductors of heat), it will melt. This fusion process, in the upward movement of the solid mantle through convection currents, is critical in the dynamics of the Earth. Decompression melting creates new oceanic crust at mid-ocean ridges, creating mantle plumes that have given rise to island chains like Hawaii. Decompression melting is the most common explanation for "Trap (geology)") basaltic floods (trapp) and oceanic plateaus, two types of large igneous provinces.

Effects of water and carbon dioxide

Another important factor that affects the melting temperature of rocks is their content of water and other volatile substances, which cause the rock to melt at temperatures below a given pressure. For example, at a depth of about 100 kilometers, peridotite begins to melt near 800 °C, in the presence of water, but in its absence it melts at about 1500 °C.[6] In subduction zones, as an oceanic plate sinks, the increase in temperature and pressure expels water from the rocks of the subducted crust, which causes the melting of the overlying mantle, giving rise to basaltic magmas and andesitics. These magmas and others derived from them were what built the volcanic island arcs throughout the Pacific Ring of Fire.

The addition of carbon dioxide (CO) is a much less important cause in the formation of magmas, although some of them are believed to form in regions of the mantle where CO predominates over water. At a depth of 70 km, carbon dioxide lowers the melting point of peridotite by 200 °C; at greater depths, the effect may be greater; It is estimated that at 200 km it is reduced between 450 °C and 600 °C. The magmas that give rise to rocks such as nephelinite), carbonatite and kimberlite may be generated by the influx of carbon dioxide into the mantle at depths greater than 70 kilometers.[7]​.