Magma

All Music Guide:

Led by classically trained drummer Christian Vander, the Paris-based Magma have been, in their way, perhaps the ultimate progressive rock group; while other artists have achieved greater commercial success and critical acclaim, Magma have typified the many ambitions and excesses of the genre that won them as many detractors as fans, even going so far as to invent their own lyrical and musical language in order to bring their unique vision to life. The son of a jazz pianist, Vander initially followed in his father's footsteps, modeling his technique on the work of John Coltrane alum Elvin Jones and starting his career with a number of jazz and R&B outfits. While in Paris in 1969, however, he was struck by a vision of Earth's spiritual and ecological future so disturbing to him that he decided to explore his fears by musical means, assembling Magma with the aid of wife and vocalist Stella, singer Klaus Blasquiz, and fusion bassists Francis Moze and Jannick Top.

As outlined on the group's eponymous 1970 double-album debut, Vander's tale -- projected to be told over the course of ten LPs -- pitted Earth against a rival planet named Kobaia. Over the course of 1971's 1,001 Centigrade and 1973's Mekanïk Destructïw Kommandoh (recorded with a choir), the story -- much of it told in native Kobaian -- unfolded to depict an Earth so uninhabitable that its citizens must flee to the nearby planet, where years of conflict culminated in the achievement of cosmic harmony and a reconciliation with the deity Ptäh. Chart success was not forthcoming, and after a few early tours of the U.S. and Britain Magma spent the middle years of the decade almost exclusively in France, where they launched records including 1974's Kohntarkosz and the next year's Live. After the commercial failure of 1976's Üdü Wüdü and 1977's Inédits, Magma essentially disbanded, although the group lived on in various forms, as alumni founded a number of loosely affiliated splinter groups to carry on Vander's work, while a number of bands -- including Art Zoyd, Univers Zero, Ensemble Nimbus, Happy Family, and Koenji Hyakkei -- would be influenced by Magma during the years to follow. In 1983, Vander himself resurfaced with the acoustic project Offering, but later returned to more grandiose designs with Les Voix de Magma, an attempt to resurrect his early material for a new generation of listeners.

In the mid-‘90s Vander re-formed Magma proper -- including Stella Vander, various musicians new to the Magma fold, and appearances by members of the band's earlier lineups -- and they began an extended period of recordings and live appearances featuring both new music and material from their "classic" period. In 1995 the album Kohntarkosz Anteria (K.A.) appeared as the second part of a trilogy that began with the Kohntarkosz album in 1974; the third and final part of the trilogy, Emehntehtt-Re, was issued in 2009. Meanwhile, Magma documented a number of their live shows on both CD and DVD releases, including the La Trilogie au Trianon CD and DVD sets recorded at the band’s 30th anniversary concerts in Paris during May 2000 and the Live in Tokyo two-CD set recorded in 2005. Magma also performed music from 35 years of the band’s history during a four-week residency at the Le Triton club in Paris during May of 2005; the Le Triton concerts were documented on the four-volume Mythes et Légendes DVD series released between 2006 and 2008.

Wikipedia:

Magma (from Greek μάγμα "mixture") is a mixture of molten or semi-molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals, dissolved gas and sometimes gas bubbles. Magma often collects in magma chambers that may feed a volcano or turn into a pluton. Magma is capable of intrusion into adjacent rocks, extrusion onto the surface as lava, and explosive ejection as tephra to form pyroclastic rock.

Magma is a complex high-temperature fluid substance. Temperatures of most magmas are in the range 700 °C to 1300 °C (or 1300 °F to 2400 °F), but very rare carbonatite melts may be as cool as 600 °C, and komatiite melts may have been as hot as 1600 °C. Most are silicate mixtures.

Environments of magma formation and compositions are commonly correlated. Environments include subduction zones, continental rift zones, mid-ocean ridges and hot spots. Despite being found in such widespread locales, the bulk of the Earth's crust and mantle is not molten. Rather, most of the Earth takes the form of a rheid, a form of solid that can move or deform under pressure. Magma, as liquid, preferentially forms in high temperature, low pressure environments within several kilometers of the Earth's surface.

Magma compositions may evolve after formation by fractional crystallization, contamination, and magma mixing. By definition rock formed of solidified magma is called igneous rock.

While the study of magma has historically relied on observing magma in the form of lava outflows, magma has been encountered in situ three times during drilling projects—twice in Iceland, and once in Hawaii.

Source [edit]

Partial melting [edit]

Melting of solid rocks to form magma is controlled by three physical parameters: its temperature, pressure, and composition. Mechanisms are discussed in the entry for igneous rock.

When rocks melt they do so incrementally and gradually; most rocks are made of several minerals, all of which have different melting points, and the physical/chemical relationships controlling melting are complex. As a rock melts, its volume changes. When enough rock is melted, the small globules of melt (generally occurring in between mineral grains) link up and soften the rock. Under pressure within the earth, as little as a fraction of a percent partial melting may be sufficient to cause melt to be squeezed from its source.

Melts can stay in place long enough to melt to 20% or even 35%, but rocks are rarely melted in excess of 50%, because eventually the melted rock mass becomes a crystal and melt mush that can then ascend en masse as a diapir, which may then cause further decompression melting.

Geochemical implications of partial melting [edit]

The degree of partial melting is critical for determining what type of magma is produced. The degree of partial melting required to form a melt can be estimated by considering the relative enrichment of incompatible elements versus compatible elements. Incompatible elements commonly include potassium, barium, caesium, rubidium.

Rock types produced by small degrees of partial melting in the Earth's mantle are typically alkaline (Ca, Na), potassic () and/or peralkaline (high aluminium to silica ratio). Typically, primitive melts of this composition form lamprophyre, lamproite, kimberlite and sometimes nepheline-bearing mafic rocks such as alkali basalts and essexite gabbros or even carbonatite.

Pegmatite may be produced by low degrees of partial melting of the crust. Some granite-composition magmas are eutectic (or cotectic) melts, and they may be produced by low to high degrees of partial melting of the crust, as well as by fractional crystallization. At high degrees of partial melting of the crust, granitoids such as tonalite, granodiorite and monzonite can be produced, but other mechanisms are typically important in producing them.

Evolution of magmas [edit]

Primary melts [edit]

When a rock melts, the liquid is a primary melt. Primary melts have not undergone any differentiation and represent the starting composition of a magma. In nature it is rare to find primary melts. The leucosomes of migmatites are examples of primary melts. Primary melts derived from the mantle are especially important, and are known as primitive melts or primitive magmas. By finding the primitive magma composition of a magma series it is possible to model the composition of the mantle from which a melt was formed, which is important in understanding evolution of the mantle.

Parental melts [edit]

Where it is impossible to find the primitive or primary magma composition, it is often useful to attempt to identify a parental melt. A parental melt is a magma composition from which the observed range of magma chemistries has been derived by the processes of igneous differentiation. It need not be a primitive melt.

For instance, a series of basalt flows are assumed to be related to one another. A composition from which they could reasonably be produced by fractional crystallization is termed a parental melt. Fractional crystallization models would be produced to test the hypothesis that they share a common parental melt.

At high degrees of partial melting of the mantle, komatiite and picrite are produced.

Migration [edit]

Magma develops within the mantle or crust when the temperature-pressure conditions favor the molten state. Magma rises toward the Earth's surface when it is less dense than the surrounding rock and when a structural zone allows movement. Magma develops or collects in areas called magma chambers. Magma can remain in a chamber until it cools and crystallizes forming igneous rock, it erupts as a volcano, or moves into another magma chamber.

Cooling of magmas [edit]

There are two known processes by which magma ceases to exist: by volcanic eruption, or by crystallization within the crust or mantle to form a pluton. In both cases the bulk of the magma eventually cools and forms igneous rocks.

When magma cools it begins to form solid mineral phases. Some of these settle at the bottom of the magma chamber forming cumulates that might form mafic layered intrusions. Magma that cools slowly within a magma chamber usually ends up forming bodies of plutonic rocks such as gabbro, diorite and granite, depending upon the composition of the magma. Alternatively, if the magma is erupted it forms volcanic rocks such as basalt, andesite and rhyolite (the extrusive equivalents of gabbro, diorite and granite, respectively).

Volcanism [edit]

During a volcanic eruption the magma that leaves the underground is called lava. Lava cools and solidifies relatively quickly compared to underground bodies of magma. This fast cooling does not allow crystals to grow large, and a part of the melt does not crystallize at all, becoming glass. Rocks largely composed of volcanic glass include obsidian, scoria and pumice.

Before and during volcanic eruptions, volatiles such as CO and HO partially leave the melt through a process known as exsolution. Magma with low water content becomes increasingly viscous. If massive exsolution occurs when magma heads upwards during a volcanic eruption, the resulting eruption is usually explosive.

Composition, melt structure and properties [edit]

Silicate melts are composed mainly of silicon, oxygen, aluminium, alkalis (sodium, potassium, calcium), magnesium and iron. Silicon atoms are in tetrahedral coordination with oxygen, as in almost all silicate minerals, but in melts atomic order is preserved only over short distances. The physical behaviours of melts depend upon their atomic structures as well as upon temperature and pressure and composition.

Viscosity is a key melt property in understanding the behaviour of magmas. More silica-rich melts are typically more polymerized, with more linkage of silica tetrahedra, and so are more viscous. Dissolution of water drastically reduces melt viscosity. Higher-temperature melts are less viscous.

Generally speaking, more mafic magmas, such as those that form basalt, are hotter and less viscous than more silica-rich magmas, such as those that form rhyolite. Low viscosity leads to gentler, less explosive eruptions.

Characteristics of several different magma types are as follows:

Temperature [edit]

At any given pressure and for any given composition of rock, a rise in temperature past the solidus will cause melting. Within the solid earth, the temperature of a rock is controlled by the geothermal gradient and the radioactive decay within the rock. The geothermal gradient averages about 25 °C/km with a wide range from a low of 5–10 °C/km within oceanic trenches and subduction zones to 30–80 °C/km under mid-ocean ridges and volcanic arc environments.

Pressure [edit]

As magma buoyantly rises it will cross the solidus-liquidus and its temperature will reduce by adiabatic cooling. At this point it will liquefy and if erupted onto the surface will form lava. Melting can also occur due to a reduction in pressure by a process known as decompression melting.

Density [edit]

Composition [edit]

It is usually very difficult to change the bulk composition of a large mass of rock, so composition is the basic control on whether a rock will melt at any given temperature and pressure. The composition of a rock may also be considered to include volatile phases such as water and carbon dioxide.

The presence of volatile phases in a rock under pressure can stabilize a melt fraction. The presence of even 0.8% water may reduce the temperature of melting by as much as 100 °C. Conversely, the loss of water and volatiles from a magma may cause it to essentially freeze or solidify.

Also a major portion of all magma is silica, which is a compound of silicon and oxygen. Magma also contains gases, which expand as the magma rises. Magma that is high in silica resists flowing, so expanding gases are trapped in it. Pressure builds up until the gases blast out in a violent, dangerous explosion. Magma that is relatively poor in silica flows easily, so gas bubbles move up through it and escape fairly gently.