What is komatiite made of?
Komatiite (/koʊˈmɑːtiˌaɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava of at least 18 wt% MgO. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content.
Why is Komatiites rare?
Komatiites are very rare igneous rocks. Komatiites are essentially restricted to the Archean (4.55 to 2.5 billion years ago), when Earth’s heat flux was much higher. Based on experiments, it’s been determined that komatiite lava, when originally erupted, was considerably hotter than any modern lava type on Earth.
How is spinifex texture formed?
The distinctive spinifex texture is formed by skeletal, platy, or acicular crystals of olivine, orthopyroxene, or clinopyroxene, or their pseudomorphs in ultramafic and mafic lavas or silicate-rich furnace slag. The complex skeletal or platy crystals may show random orientation, or may display a preferred arrangement.
What is the cooling rate of komatiite?
Donaldson (1982) estimated that cooling rates in the A3 layer of a typical 5–10 m thick komatiite flow were <1 C/h. In contrast, to reproduce the dendritic mor- phology of platy spinifex olivine crystals in normal dynamic cooling laboratory experiments requires cooling rates >50 C/h (Donaldson, 1982).
Why are there no longer ultramafic lava flows forming on Earth?
Structure of the Earth. Image taken from here. Although ultramafic rock makes up most of the Earth, geologists rarely find ultramafic rocks on Earth’s thin crust. This is because when the Earth’s mantle melts to produce magmas, it does not melt 100%.
What is Trachytic texture?
Trachytic is a texture of extrusive rocks in which the groundmass contains little volcanic glass and consists predominantly of minute tabular crystals, namely, sanidine microlites. The microlites are parallel, forming flow lines along the directions of lava flow and around inclusions.
How do you identify peridotite?
Classic peridotite is bright green with some specks of black, although most hand samples tend to be darker green. Peridotitic outcrops typically range from earthy bright yellow to dark green in color; this is because olivine is easily weathered to iddingsite.
How do you identify andesite?
Andesite is usually light to dark gray in colour, due to its content of hornblende or pyroxene minerals. but can exhibit a wide range of shading. Darker andesite can be difficult to distinguish from basalt, but a common rule of thumb, used away from the laboratory, is that andesite has a color index less than 35.
What is difference between magma and lava?
Scientists use the term magma for molten rock that is underground and lava for molten rock that breaks through the Earth’s surface.
What happens if you touch lava?
Lava won’t kill you if it briefly touches you. You would get a nasty burn, but unless you fell in and couldn’t get out, you wouldn’t die. With prolonged contact, the amount of lava “coverage” and the length of time it was in contact with your skin would be important factors in how severe your injuries would be!
What kind of rock is the komatiite rock?
The rock type komatiite is particularly diagnostic of those volcanic sequences and is almost exclusively restricted to the Archean Eon. The cratons were tectonically stabilized by voluminous granite intrusions toward the end of the Archean and were then covered by clastic sediments, some of which contain economically important….
What kind of minerals are found in komatiite lava?
A variety of ultramafic lavas that crystallize from high temperature magmas with 18% to 32% MgO. They often form pillows and have chilled flow-tops and usually display well-developed spinifex textures with intergrown skeletal and bladed olivine and pyroxene crystals set in abundant glass.
Where are the komatiites found in South Africa?
The term was originally applied by Viljoen and Viljoen (1969) to basaltic and ultramafic lavas near the Komati river, Barberton Mountain Land, Transvaal, South Africa. Nickel-copper sulfide mineral deposits may be associated with komatiites.
What kind of magnesium does a komatiite have?
Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene.