Magmatic water

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Magmatic water, also known as juvenile water, is an aqueous phase in equilibrium with minerals that have been dissolved by magma deep within the Earth's crust and is released to the atmosphere during a volcanic eruption. It plays a key role in assessing the crystallization of igneous rocks, particularly silicates, as well as the rheology and evolution of magma chambers. Magma is composed of minerals, crystals and volatiles in varying relative natural abundance. [1] Magmatic differentiation varies significantly based on various factors, most notably the presence of water. [2] An abundance of volatiles within magma chambers decreases viscosity and leads to the formation of minerals bearing halogens, including chloride and hydroxide groups. In addition, the relative abundance of volatiles varies within basaltic, andesitic, and rhyolitic magma chambers, leading to some volcanoes being exceedingly more explosive than others. Magmatic water is practically insoluble in silicate melts but has demonstrated the highest solubility within rhyolitic melts. An abundance of magmatic water has been shown to lead to high-grade deformation, altering the amount of δ18O and δ2H within host rocks.

Contents

Composition

Magma exists in three main forms that vary in composition. [3] When magma crystallizes within the crust, it forms an extrusive igneous rock. Dependent on the composition of the magma, it may form either rhyolite, andesite, or basalt. [3] Volatiles, particularly water and carbon dioxide, significantly impact the behavior of each form of magma differently. [4] , [2] Magma with a high concentration of volatiles has a significant reduction in temperature of up to hundreds of degrees, which reduces its inherent viscosity. [5] The behavior of magma is also altered by varying mineralogic compositions, which is noted in Figure 1. For instance, magmatic water leads to the crystallization of several minerals abundant in hydroxyl- or halogenated-groups, including garnets. Analyses of these minerals can be used to analyze the conditions of formation in the interior of rocky planets. [5] , [6]

Figure 1. Mineralogic Composition of Rhyolitic, Andesitic, and Basaltic Magmas Igneous rocks.jpg
Figure 1. Mineralogic Composition of Rhyolitic, Andesitic, and Basaltic Magmas

Volatiles

Volatiles are present in nearly all magma in different concentrations. Examples of volatiles within magma include water, carbon dioxide, and halogen gases. [1] High pressures allow these volatiles to stay relatively stable within solution. [1] However, over time, as the magmatic pressure decreases, volatiles will rise out of solution in the gaseous phase, further decreasing the magmatic pressure. [1] These pressure differences cause drastic differences in the volume of a magma. [1] Pressure difference causes some forms of volcanoes to be highly explosive and others to be effusive. [1]

Mineralogy

An example of a mineral containing hydroxyl groups is garnet. Garnet is an anhydrous mineral commonly analyzed within geological subdisciplines because of its general stability. One study analyzed the presence of garnets within the upper mantle through infrared spectroscopy and showed absorption at approximately 3500 cm−1, which is consistent with the presence of hydroxyl groups. These garnets have been shown to vary in composition dependent on its geographic origin. [6] One particular study in Southern Africa determined concentrations ranging from 1 ppm - 135 ppm. [6] However, this is significantly lower than the hydroxyl content in regions such as the Colorado Plateau. It was also demonstrated that there is an inverse correlation regarding the concentration of OH and Mg + Fe.

Basaltic magma

Basaltic magma is the most abundant in iron, magnesium, and calcium but the lowest in silica, potassium, and sodium. [1] , [3] The composition of silica within basaltic magma ranges from 45-55 weight percent (wt.%), or mass fraction of a species. [1] It forms in temperatures ranging from approximately 1830 °F to 2200 °F. [1] , [3] Basaltic magma has the lowest viscosity and volatiles content, yet still may be up to 100,000 times more viscous than water. [1] Because of its low viscosity, this is the least explosive form of magma. Basaltic magma may found in regions such as Hawaii, known for its shield volcanoes. [1] , [7]

Basaltic magma forms minerals such as calcium-rich plagioclase feldspar and pyroxene. The water composition of basaltic magma varies dependent on the evolution of the magma chamber. Arc magmas, such as Izarú in Costa Rica, range from 3.2-3.5 wt.%. [8]

Andesitic magma

Andesitic magma is an intermediate magma and is approximately evenly dispersed regarding iron, magnesium, calcium, sodium, and potassium. [1] [3] The silica composition of andesitic magma ranges from 55 - 65 wt.%. [1] It forms in temperatures ranging from approximately 1470 °F to 1830 °F. [1] , [3] Andesitic magma has an intermediate viscosity and volatiles content. [1] It forms minerals such as plagioclase feldspar, mica, and amphibole.

Rhyolitic magma

Rhyolitic magma is felsic and the most abundant in silica, potassium, and sodium but the lowest in iron, magnesium, and calcium. [1] [3] The silica composition of rhyolitic magma ranges from 65-75 wt.%. [1] It forms in the lowest temperature range, from about 1200 °F to 1470 °F. [1] , [3] Rhyolitic magma has the highest viscosity and gas content. [1] It produces the most explosive volcanic eruptions, including the catastrophic eruption of Mount Vesuvius. [1] It forms minerals such as orthoclase feldspar, sodium-rich plagioclase feldspar, quartz, mica, and amphibole.

Water in silicate melts

Precipitation of minerals is affected by water solubility within silicate melts, which typically exists as hydroxyl groups bound to Si4+ or Group 1 and Group 2 cations in concentrations ranging from approximately 6-7 wt. %. [9] , [10] Specifically, the equilibrium of water and dissolved oxygen yields hydroxides, where the Keq has been approximated between 0.1 and 0.3. [10]

This inherent solubility is low yet varies greatly depending on the pressure of the system. Rhyolitic magmas have the highest solubility, ranging from approximately 0% at the surface to nearly 10% at 1100 °C and 5 kbar. Degassing occurs when hydrous magma is uplifted, gradually converting the dissolved water to aqueous phase. This aqueous phase is typically abundant in volatiles, metals (copper, lead, zinc, silver and gold), and Group 1 and Group 2 cations. Dependent on which cation the hydroxyl is bound to, it significantly impacts the properties of a volcanic eruption, particularly its explosiveness. [9] During unusually high temperature and pressure conditions exceeding 374 °C and 218 bar, water enters a supercritical fluid state and becomes no longer a liquid or a gas. [9]

Stable isotope data

Isotopic data from various locations within the Mid-Atlantic Ridge indicates the presence of mafic-to-felsic intrusive igneous rocks, including gabbro, diorite, and plagiogranite. [11] These rocks showed high-grade metamorphism because of the presence of magmatic water, exceeding 600 °C. This deformation depleted host rocks of 18O, leading to further analysis of the ratio of 18O to 16O (δ18O). [11]

Water in equilibrium with igneous melts should bear the same isotopic signature for 18O and δ2H. However, isotopic studies of magmatic water have demonstrated similarities to meteoric water, indicating circulation of magmatic and meteoric groundwater systems. [12]

Isotopic analyses of fluid inclusions indicate a wide range of δ18O and δ2H content. [13] Studies within these environments have shown an abundance of 18O and depletion in 2H relative to SMOW and meteoric waters. Within ore deposits, fluid inclusion data showed that the presence of δ18O vs δ2H are within the expected range.

See also

Related Research Articles

<span class="mw-page-title-main">Mafic</span> Silicate mineral or igneous rock that is rich in magnesium and iron

A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt, diabase and gabbro. Mafic rocks often also contain calcium-rich varieties of plagioclase feldspar. Mafic materials can also be described as ferromagnesian.

<span class="mw-page-title-main">Magma</span> Hot semifluid material found beneath the surface of Earth

Magma is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural satellites. Besides molten rock, magma may also contain suspended crystals and gas bubbles.

<span class="mw-page-title-main">Basalt</span> Magnesium- and iron-rich extrusive igneous rock

Basalt is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron exposed at or very near the surface of a rocky planet or moon. More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro. The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the Solar System. For example, the bulk of the plains of Venus, which cover ~80% of the surface, are basaltic; the lunar maria are plains of flood-basaltic lava flows; and basalt is a common rock on the surface of Mars.

<span class="mw-page-title-main">Plagioclase</span> Type of feldspar

Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series. This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796–1872) in 1826. The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or "record-groove" effect.

<span class="mw-page-title-main">Rhyolite</span> Igneous, volcanic rock, of felsic (silica-rich) composition

Rhyolite is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent to granite.

<span class="mw-page-title-main">Dacite</span> Volcanic rock intermediate in composition between andesite and rhyolite

Dacite is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. It is composed predominantly of plagioclase feldspar and quartz.

<span class="mw-page-title-main">Andesite</span> Type of volcanic rock

Andesite is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende.

<span class="mw-page-title-main">Extrusive rock</span> Mode of igneous volcanic rock formation

Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. In contrast, intrusive rock refers to rocks formed by magma which cools below the surface.

<span class="mw-page-title-main">Xenolith</span> Rock inside a rock with a different composition

A xenolith is a rock fragment that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock entrained during magma ascent, emplacement and eruption. Xenoliths may be engulfed along the margins of a magma chamber, torn loose from the walls of an erupting lava conduit or explosive diatreme or picked up along the base of a flowing body of lava on the Earth's surface. A xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes. Xenoliths can be non-uniform within individual locations, even in areas which are spatially limited, e.g. rhyolite-dominated lava of Niijima volcano (Japan) contains two types of gabbroic xenoliths which are of different origin - they were formed in different temperature and pressure conditions.

<span class="mw-page-title-main">Effusive eruption</span> Type of volcanic eruption characterized by steady lava flow

An effusive eruption is a type of volcanic eruption in which lava steadily flows out of a volcano onto the ground.

<span class="mw-page-title-main">Cumulate rock</span> Igneous rocks formed by the accumulation of crystals from a magma either by settling or floating.

Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. Cumulate rocks are named according to their texture; cumulate texture is diagnostic of the conditions of formation of this group of igneous rocks. Cumulates can be deposited on top of other older cumulates of different composition and colour, typically giving the cumulate rock a layered or banded appearance.

In geology, igneous differentiation, or magmatic differentiation, is an umbrella term for the various processes by which magmas undergo bulk chemical change during the partial melting process, cooling, emplacement, or eruption. The sequence of magmas produced by igneous differentiation is known as a magma series.

<span class="mw-page-title-main">Fractional crystallization (geology)</span> Process of rock formation

Fractional crystallization, or crystal fractionation, is one of the most important geochemical and physical processes operating within crust and mantle of a rocky planetary body, such as the Earth. It is important in the formation of igneous rocks because it is one of the main processes of magmatic differentiation. Fractional crystallization is also important in the formation of sedimentary evaporite rocks.

Volatiles are the group of chemical elements and chemical compounds that can be readily vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as refractory substances.

<span class="mw-page-title-main">Melt inclusion</span>

A melt inclusion is a small parcel or "blobs" of melt(s) that is entrapped by crystals growing in magma and eventually forming igneous rocks. In many respects it is analogous to a fluid inclusion within magmatic hydrothermal systems. Melt inclusions tend to be microscopic in size and can be analyzed for volatile contents that are used to interpret trapping pressures of the melt at depth.

<span class="mw-page-title-main">Lava</span> Molten rock expelled by a volcano during an eruption

Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or underwater, usually at temperatures from 800 to 1,200 °C. The volcanic rock resulting from subsequent cooling is also often called lava.

<span class="mw-page-title-main">Igneous rock</span> Rock formed through the cooling and solidification of magma or lava

Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava.

Tectonic–climatic interaction is the interrelationship between tectonic processes and the climate system. The tectonic processes in question include orogenesis, volcanism, and erosion, while relevant climatic processes include atmospheric circulation, orographic lift, monsoon circulation and the rain shadow effect. As the geological record of past climate changes over millions of years is sparse and poorly resolved, many questions remain unresolved regarding the nature of tectonic-climate interaction, although it is an area of active research by geologists and palaeoclimatologists.

<span class="mw-page-title-main">Crystal mush</span>

A crystal mush is magma that contains a significant amount of crystals suspended in the liquid phase (melt). As the crystal fraction makes up less than half of the volume, there is no rigid large-scale three-dimensional network as in solids. As such, their rheological behavior mirrors that of absolute liquids.

I-type granites are a category of granites originating from igneous sources, first proposed by Chappell and White (1974). They are recognized by a specific set of mineralogical, geochemical, textural, and isotopic characteristics that indicate, for example, magma hybridization in the deep crust. I-type granites are saturated in silica but undersaturated in aluminum; petrographic features are representative of the chemical composition of the initial magma. In contrast S-type granites are derived from partial melting of supracrustal or "sedimentary" source rocks.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Nelson, Stephen (September 2015). "Volcanoes, Magma, and Volcanic Eruptions". Tulane University EENS 3050. Retrieved March 1, 2021.
  2. 1 2 Petrelli, M.; El Omari, K.; Spina, L.; Le Guer, Y.; La Spina, G.; Perugini, D. (2018-02-22). "Timescales of water accumulation in magmas and implications for short warning times of explosive eruptions". Nature Communications. 9 (1): 770. Bibcode:2018NatCo...9..770P. doi: 10.1038/s41467-018-02987-6 . ISSN   2041-1723. PMC   5823946 . PMID   29472525.
  3. 1 2 3 4 5 6 7 8 "Magma". National Geographic Society. 2019-04-05. Retrieved 2021-02-26.
  4. ↑ "What does magmatic water mean?". www.definitions.net. Retrieved 2021-02-21.
  5. 1 2 "Igneous rock - Assimilation". Encyclopedia Britannica. Retrieved 2021-02-27.
  6. 1 2 3 Bell, David. "Hydroxyl in mantle minerals" (PDF). California Institute of Technology Pasadena, California.
  7. ↑ Watson, John (May 1997). "Eruptive Style: Powerful but Unsually [sic] Benign". USGS. Retrieved March 1, 2021.
  8. ↑ Benjamin, Ezra R.; Plank, Terry; Wade, Jennifer A.; Kelley, Katherine A.; Hauri, Erik H.; Alvarado, Guillermo E. (2007-11-15). "High water contents in basaltic magmas from Irazú Volcano, Costa Rica". Journal of Volcanology and Geothermal Research. 168 (1): 68–92. Bibcode:2007JVGR..168...68B. doi:10.1016/j.jvolgeores.2007.08.008. ISSN   0377-0273.
  9. 1 2 3 Le Losq, Charles; Mysen, Bjorn O.; Cody, George D. (2015-08-14). "Water and magmas: insights about the water solution mechanisms in alkali silicate melts from infrared, Raman, and 29Si solid-state NMR spectroscopies". Progress in Earth and Planetary Science. 2 (1): 22. Bibcode:2015PEPS....2...22L. doi: 10.1186/s40645-015-0052-7 . hdl: 1885/153807 . ISSN   2197-4284.
  10. 1 2 Stolper, Edward (1982-12-01). "The speciation of water in silicate melts". Geochimica et Cosmochimica Acta. 46 (12): 2609–2620. Bibcode:1982GeCoA..46.2609S. doi:10.1016/0016-7037(82)90381-7. ISSN   0016-7037.
  11. 1 2 Stakes, Debra (1991). "Oxygen and hydrogen isotope compositions of oceanic plutonic rocks: high-temperature deformation and metamorphism of oceanic layer 3" (PDF). The Geochemical Society, Special Publication. 3: 77–90.
  12. ↑ Hall, Anthony (1987). Igneous petrology. Harlow, Essex, England: Longman Scientific & Technical. ISBN   0-470-20781-7. OCLC   14098243.
  13. ↑ Guilbert, John M. (1986). The geology of ore deposits. Charles F., Jr. Park, Charles F., Jr. Park. New York: W.H. Freeman. ISBN   0-7167-1456-6. OCLC   12081840.
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