Adakite is a petrologic

Petrology

Petrology is the branch of geology that studies rocks, and the conditions in which rocks form....

 term for volcanic or intrusive igneous rocks that are interpreted to form in subduction zones from the mixing of mantle material with felsic

Felsic

The word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....

 partial melts of descending slabs of oceanic crust

Oceanic crust

Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...

 basalt

Basalt

Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...

. Adakites include a range of resulting rock types: they are recognized by specific chemical and isotopic characteristics, mainly high 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. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...

/Y

Yttrium

Yttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and it has often been classified as a "rare earth element". Yttrium is almost always found combined with the lanthanides in rare earth minerals and is...

 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 the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...

/Yb

Ytterbium

Ytterbium is a chemical element with the symbol Yb and atomic number 70. A soft silvery metallic element, ytterbium is a rare earth element of the lanthanide series and is found in the minerals gadolinite, monazite, and xenotime. The element is sometimes associated with yttrium or other related...

 ratios and low Y and Yb trace element

Trace element

In analytical chemistry, a trace element is an element in a sample that has an average concentration of less than 100 parts per million measured in atomic count, or less than 100 micrograms per gram....

 content. Adakites have, in the literature, the following reported composition: SiO2 >56 wt percent, Al2O3 >15 wt percent, MgO normally <3 wt percent, Mg number 0.5, Sr >400 ppm, Y <18 ppm, Yb <1.9 ppm, Ni >20 ppm, Cr >30 ppm, >Sr/Y 20, La/Yb >20, and 87Sr/86Sr <0.7045.

There is some debate as to the process that produces adakites. Low magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

 adakites may be representative of relatively pure partial melting of a subducting basalt, whereas high magnesium adakite or high magnesium andesite

Andesite

Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...

s may represent melt contamination with the peridotite

Peridotite

A peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron...

s of the overlying mantle wedge

Mantle wedge

A mantle wedge is a zone of mantle, triangular in cross–section, that lies between subducting and overriding tectonic plates. Flow inside the wedge is aligned with plate motions. Flux melting of material within wedge due to the release of volatiles from the underlying subducting slab results in...

. Adakites have also been reported from the continent-continent collision zone beneath Tibet.