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
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates a ...
eruption. It plays a key role in assessing the crystallization of
igneous rock
Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma o ...
s, particularly
silicates
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name i ...
, as well as the
rheology
Rheology (; ) is the study of the flow of matter, primarily in a fluid (liquid or gas) state, but also as "soft solids" or solids under conditions in which they respond with Plasticity (physics), plastic flow rather than deforming Elasticity (phy ...
and evolution of
magma chambers.
Magma
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 sa ...
is composed of
minerals
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed ...
,
crystals
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
and
volatiles
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.
On planet Earth, the term ...
in varying relative abundance.
Magmatic differentiation varies significantly based on various factors, most notably the presence of water.
An abundance of volatiles within magma chambers decreases
viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the inte ...
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 δ
18O and δ
2H within host rocks.
Composition
Magma exists in three main forms that vary in composition.
When magma crystallizes within the
crust, it forms an
extrusive
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 contra ...
igneous rock. Dependent on the composition of the magma, it may form either
rhyolite,
andesite
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 predo ...
, or
basalt
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
.
Volatiles, particularly water and carbon dioxide, significantly impact the behavior of each form of magma differently.
, Magma with a high concentration of volatiles have a significant reduction in temperature of up to hundreds of degrees, which reduces its inherent viscosity.
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.
,
Volatiles
Volatiles are present in nearly all magma in different concentrations. Examples of volatiles within magma include water, carbon dioxide, and
halogen gases.
High pressures allow these volatiles to stay relatively stable within solution.
However, over time, as the magmatic pressure decreases, volatiles will rise out of solution in the gaseous phase, further decreasing the magmatic pressure.
These pressure differences cause drastic differences in the volume of a magma.
Pressure difference causes some forms of volcanoes to be highly
explosive and others to be
effusive.
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
Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or function ...
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.
One particular study in
Southern Africa
Southern Africa is the southernmost subregion of the African continent, south of the Congo and Tanzania. The physical location is the large part of Africa to the south of the extensive Congo River basin. Southern Africa is home to a number o ...
determined concentrations ranging from 1 ppm - 135 ppm.
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.
, The composition of silica within basaltic magma ranges from 45-55 weight percent (wt.%), or mass fraction of a species.
It forms in temperatures ranging from approximately 1830 °F to 2200 °F.
, Basaltic magma has the lowest viscosity and volatiles content, yet still may be up to 100,000 times more viscous than water.
Because of its low viscosity, this is the least explosive form of magma. Basaltic magma may found in regions such as
Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...
, known for its
shield volcanoes
A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more vi ...
.
,
Basaltic magma forms minerals such as calcium-rich
plagioclase 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 prop ...
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.%.
Andesitic magma
Andesitic magma is an intermediate magma and is approximately evenly dispersed regarding iron, magnesium, calcium, sodium, and potassium.
The silica composition of andesitic magma ranges from 55 - 65 wt.%.
It forms in temperatures ranging from approximately 1470 °F to 1830 °F.
, Andesitic magma has an intermediate viscosity and volatiles content.
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.
The silica composition of rhyolitic magma ranges from 65-75 wt.%.
It forms in the lowest temperature range, from about 1200 °F to 1470 °F.
, Rhyolitic magma has the highest viscosity and gas content.
It produces the most explosive volcanic eruptions, including the catastrophic eruption of
Mount Vesuvius
Mount Vesuvius ( ; it, Vesuvio ; nap, 'O Vesuvio , also or ; la, Vesuvius , also , or ) is a somma-stratovolcano located on the Gulf of Naples in Campania, Italy, about east of Naples and a short distance from the shore. It is one of ...
.
It forms minerals such as
orthoclase
Orthoclase, or orthoclase feldspar ( endmember formula K Al Si3 O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture," because its two cleavage planes are at right angles ...
feldspar, sodium-rich plagioclase feldspar,
quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
, 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 Si
4+ or
Group 1 Group 1 may refer to:
* Alkali metal, a chemical element classification for Alkali metal
* Group 1 (racing), a historic (until 1981) classification for Touring car racing, applied to standard touring cars. Comparable to modern FIA Group N
* Group On ...
and
Group 2 The term Group 2 may refer to:
* Alkaline earth metal, a chemical element classification
* Astronaut Group 2, also known as The New Nine, the second group of astronauts selected by NASA in 1962
* Group 2 (racing), an FIA classification for cars in ...
cations in concentrations ranging from approximately 6-7 wt. %.
, Specifically, the equilibrium of water and dissolved oxygen yields hydroxides, where the
Keq has been approximated between 0.1 and 0.3.
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
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
,
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
,
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
,
silver
Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
and
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...
), 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.
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.
Stable isotope data
Isotopic data from various locations within the
Mid-Atlantic Ridge
The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, the ridge separates the North ...
indicates the presence of mafic-to-felsic intrusive igneous rocks, including
gabbro
Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...
,
diorite
Diorite ( ) is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-sili ...
, and
plagiogranite.
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).
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
Meteoric water is the water derived from precipitation (snow and rain). This includes water from lakes, rivers, and icemelts, which all originate from precipitation indirectly. While the bulk of rainwater or meltwater from snow and ice reaches the ...
, indicating circulation of magmatic and meteoric groundwater systems.
Isotopic analyses of
fluid inclusions indicate a wide range of δ
18O and δ
2H content.
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 δ
18O vs δ
2H are within the expected range.
See also
*
Connate fluids
References
{{DEFAULTSORT:Magmatic Water
Igneous petrology
Geochemistry
Water
Scientific problems