Boninite

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Boninite

Boninite is a mafic

Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term was derived by contracting "magnesium" and "ferric"....
extrusive rock

Rock (geology)

In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock....
high in both magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.Magnesium, an alkaline earth metal, is the ninth most abundance of the chemical elements in the universe by mass....
and silica, formed in fore-arc environments, typically during the early stages of subduction. The rock is named for its occurrence in the Izu-Bonin arc south of Japan

Japan

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Boninite is a mafic

Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term was derived by contracting "magnesium" and "ferric"....
extrusive rock

Rock (geology)

In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock....
high in both magnesium

Magnesium

Japan

Japan is an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south....
. It is characterized by extreme depletion in incompatible trace elements that are not fluid mobile (e.g., the heavy rare earth elements plus Nb, Ta, Hf) but variable enrichment in the fluid mobile elements (e.g., Rb, Ba, K). They are found almost exclusively in the fore-arc of primitive island arcs (that is, closer to the trench) and in ophiolite complexes thought to represent former fore-arc settings.

Boninite is considered to be a primitive andesite

Andesite

Andesite is an igneous rock, volcanic rock, of Igneous rock#Chemical classification, with aphanitic to porphyritic texture. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende....
derived from melting of metasomatised

Metasomatism

Metasomatism is the chemical alteration of a Rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or Metamorphism source....
mantle

Mantle (geology)

The mantle is a part of an astronomical object. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers....
.

Similar Archean

Archean

The Archean is a geology eon before the Proterozoic and Paleoproterozoic, before 2.5 Ga . Instead of being based on stratigraphy, this date is defined chronometrically....
intrusives called sanukitoid

Sanukitoid

Sanukitoids are a variety of high-Mg granitoid found in convergent margin settings. The term "sanukitoid" was originally used to define a variety of Archean plutonic rock, but now also includes younger rocks with similar geochemical characteristics ....
s have been reported in the rocks of several early craton

Craton

A craton is an old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for at least 500 million years....
s.

Petrology

Boninite typically consists of phenocryst

Phenocryst

A phenocryst is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock Matrix of a porphyritic igneous rock....
s of pyroxene

Pyroxene

The pyroxenes are a group of important rock-forming silicate minerals found in many igneous and metamorphic rock rock . They share a common structure comprised of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems....
s and olivine

Olivine

The mineral olivine is a magnesium iron Silicate minerals with the formula 2siliconoxygen4. It is one of the most common minerals on Earth, and has also been identified in meteorites and on the Moon, Mars, and comet Wild 2....
in a crystallite-rich glassy matrix

Matrix (geology)

The matrix or groundmass of rock is the fine-grained mass of material in which larger grains or crystals are embedded.The matrix of an igneous rock consists of fine-grained, often microscopic, crystals in which larger crystals are embedded....
.

Geochemistry

Boninite is defined by

high magnesium content (MgO
MGO

MGO may refer to;*MgO, the chemical formula of Magnesium oxide.*MGO, abbreviation of Methylglyoxal.*Metal Gear Online, an online video game....
= 8-15%)
low titanium
Titanium

Titanium is a chemical element with the symbol Ti and atomic number 22. Sometimes called the ?space age metal?, it has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver colour....
(TiO₂
Titanium dioxide

Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula titaniumoxygen2....
< 0.5%)
silica content is 57 - 60%
high Mg/(Mg + Fe
Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
) (0.55-0.83)
Mantle-normal compatible
Compatibility (geochemistry)

In geochemistry, compatibility is a measure of how readily a particular trace element will substitute for a major element within a mineral.Compatibility of an ion is controlled by two things: its valence and its ionic radius....
elements Ni
Nickel

Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge....
= 70-450 parts per million, Cr
Chromium

Chromium is a chemical element which has the symbol Cr and atomic number 24. It is a steely-gray, Lustre , hard metal that takes a high polish and has a high melting point....
= 200-1800 ppm
Ba
Barium

Barium is a chemical element. It has the symbol Ba, and atomic number 56. Barium is a soft silvery metallic alkaline earth metal. It is never found in nature in its pure form due to its reactivity with Earth's atmosphere....
, Sr
Strontium

Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically....
, LREE
Ree

Ree or REE may have one of the following meanings.*God, Of Reestablishmentarianism*Lough Ree, an Irish lake*Arikara, a Native American tribe ...
enrichments compared to tholeiite
Tholeiite

Tholeiitic basalt is an igneous rock, a type of basalt. Like all basalt, the rock type is dominated by clinopyroxene plus plagioclase, with minor iron-titanium oxides....
Characteristic Ti/Zr
Zirconium

Zirconium is a chemical element with the symbol Zr and atomic number 40. It is a lustrous, gray-white, strong transition metal that resembles titanium....
ratios (23-63) and La
Lanthanum

Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is a lanthanoid....
/Yb
Yb

YB is an acronym for:* Ytterbium, the chemical element* Young Buck, Rapper* BSC Young Boys, a Berne soccer club* the chemical sign for the element Ytterbium...
ratios (0.6-4.7)

Genesis

Boninite magma is formed by second stage melting in forearc

Forearc

A forearc is a depression in the sea floor located between a subduction zone and an associated volcanic arc. It is typically filled with sediments from the adjacent landmass and the island arc in addition to trapped oceanic crustal material....
s via hydration

Mineral hydration

Mineral hydration is an inorganic chemical reaction where water is added to the crystal structure of a mineral, usually creating a new mineral, usually called a hydrate....
of previously depleted mantle within the mantle wedge above a subducted slab

Subduction

In geology, subduction is the process that takes place at convergent boundary by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge....
, causing further melting of the already depleted peridotite

Peridotite

A peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic and ultrabasic, as the rock contains less than 45% silica....
. The extremely low content of titanium, which is an incompatible element within melting of peridotite is the result of previous melting events that removed most of the incompatible elements from the residual mantle source. The first stage melting typically forms island arc basalt.

Boninite attains its high magnesium and very low titanium content via high degrees of partial melting within the convecting

Mantle convection

Mantle convection is the slow creeping motion of Earth's rocky Mantle in response to perpetual gravitationally unstable variations in its density....
mantle wedge. The high degrees of partial melting are caused by the high water content of the mantle. With the addition of slab-derived volatiles, and incompatible elements derived from the release of low-volume partial melts of the subducted slab, the depleted mantle in the mantle wedge undergoes melting.

Evidence for variable enrichment or depletion of incompatible elements suggests that boninites are derived from refractory peridotite which has been metasomatically enriched in LREE, Sr, Ba and alkali

Alkali

In chemistry, an alkali is a Base , Ionic compound salt of an alkali metal or alkaline earth metal Chemical element. Alkalis are best known for being Base s that dissolve in water....
s. Enrichment in Ba, Sr and alkalis may result from a component derived from subducted oceanic crust. This is envisaged as contamination from the underlying subducted slab, either as a sedimentary source or as melts derived from the dehydrating slab.

Boninites can be derived from the peridotite residue of earlier arc tholeiite generation which is metasomatically enriched in LREE before boninite volcanism

Volcano

A volcano is an opening, or rupture, in a planet's surface or Crust , which allows hot, molten rock, ash, and gases to escape from below the surface....
, or arc tholeiites and boninites can be derived from a variably depleted peridotite source which has been variably metasomatised in LREE.

Areas of fertile peridotite would yield tholeiites while refractory areas would yield boninites.

Examples

***Examples of Boninite***
Name	Location	Age	Comments
Bonin Islands	Pacific Ocean Pacific Ocean The Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Mare Pacificum, "peaceful sea", bestowed upon it by the Portugal explorer Ferdinand Magellan....	Eocene Eocene The Eocene Geologic time scale is a major division of the geologic timescale and the second epoch of the Palaeogene period in the Cenozoic era....	mostly volcanic breccia Breccia Breccia is a rock composed of angular fragments of several minerals or rocks in a Matrix , that is a Cementation material, that may be similar or different in composition to the fragments.... s and pillow lava flows
Cape Vogel	Papua New Guinea Papua New Guinea Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands ....	Paleocene Paleocene The Paleocene or Palaeocene, "early dawn of the recent" is a geologic epoch that lasted from 65.5 ? 0.3 Mega-annum to 55.8 ? 0.2 Ma . It is the first epoch of the Palaeogene Period in the modern Cenozoic era ....
Troodos	Cyprus Cyprus Cyprus , officially the Republic of Cyprus , is an island country situated in the eastern Mediterranean Sea, east of Greece, west of Lebanon, Syria, and Israel, south of Turkey and north of Egypt....	Cretaceous Cretaceous The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....	upper pillow lavas of ophiolite complex
Guam Guam Guam , officially the Territory of Guam, is an island in the western Pacific Ocean and is an organized, unincorporated insular area of the United States....	Pacific Ocean Pacific Ocean The Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Mare Pacificum, "peaceful sea", bestowed upon it by the Portugal explorer Ferdinand Magellan....	Paleogene Paleogene The Paleogene is a geologic period that began 65.5 ? 0.3 and ended 23.03 ? 0.05 million years ago and comprises the first part of the Cenozoic era....	late Eocene to early Oligocene Oligocene The Oligocene is a geologic epoch of the Paleogene Geologic Timescale and extends from about 33.9 million to 23 million years before the present....
Setouchi	Japan Japan Japan is an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south....	Miocene Miocene The Miocene is a Geologic time scale of the Neogene period and extends from about 23.03 to 5.33 million years before the present. As with other older geologic periods, the rock beds that define the start and end are well identified but the exact dates of the start and end of the period are uncertain....	sanukitoid Sanukitoid Sanukitoids are a variety of high-Mg granitoid found in convergent margin settings. The term "sanukitoid" was originally used to define a variety of Archean plutonic rock, but now also includes younger rocks with similar geochemical characteristics .... s, 13 million years old
Baja California Baja California Baja California is the northernmost States of Mexico of Mexico. Before becoming a state in 1953, the area was known as the North Territory of Baja California....	Mexico Mexico The United Mexican States , commonly known as Mexico , is a federalism constitutionalism republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of Mexico....	Miocene	14 to 12 million years old, includes bajaite
New Caledonia New Caledonia New Caledonia , is a "sui generis collectivity" of France located in the subregion of Melanesia in the Oceania. It comprises a main island , the Loyalty Islands, and several smaller islands....	Pacific Ocean Pacific Ocean The Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Mare Pacificum, "peaceful sea", bestowed upon it by the Portugal explorer Ferdinand Magellan....	Mesozoic Mesozoic The Mesozoic Era is one of three Geologic time scale of the Phanerozoic eon . The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the 'Mesozoic' was 'Secondary' ....	Permian Permian The PermianThe term "Permian" was introduced into geology in 1841 by Sir Roderick Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian system" after the ancient kingdom... -Triassic Triassic The Triassic is a geologic period that extends from about 251 to 199 annum . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic.... and Cretaceous age
Mariana Trench Mariana Trench The Mariana Trench is the deepest part of the world's oceans, and the deepest location on the surface of the Earth's Crust . It has a maximum depth of about 10,911 meters , and is located in the western North Pacific Ocean, to the east and south of the Mariana Islands, near Guam....	Pacific Ocean Pacific Ocean The Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Mare Pacificum, "peaceful sea", bestowed upon it by the Portugal explorer Ferdinand Magellan....	Eocene