What minerals are in komatiites?
Komatiite:
- An ultramafic, volcanic rock that is primarily composed of the minerals pyroxene and olivine.
- A very unusual and rare volcanic rock type that is not produced today.
- A rock type whose hotly– and wetly– debated origin sometimes galvanizes geologists to shouting matches, fist fights, and drinking contests.
Why is komatiites rare?
Komatiites are rare rocks; almost all komatiites were formed during the Archaean Eon (4.0–2.5 billion years ago), with few younger (Proterozoic or Phanerozoic) examples known. This restriction in age is thought to be due to cooling of the mantle, which may have been 100–250 °C (212–482 °F) hotter during the Archaean.
What are komatiites rare?
Komatiites are very rare igneous rocks. They are one variety of extrusive ultramafic igneous rock (although a komatiite in Canada has been interpreted to be an intrusive sill). Komatiites are essentially restricted to the Archean (4.55 to 2.5 billion years ago), when Earth’s heat flux was much higher.
Is komatiite fine grained?
(1977). A1—This uppermost layer is aphyric or extremely fine grained and only a few mm to a few cm thick. A2—Random spinifex texture: Gradationally under A1, there is a layer of apparent needle-like, but actually blade-like, skeletal crystals of olivine with a random orientation (Figure 49.4(A)).
What type of igneous rock is Websterite?
ultramafic igneous rock
Websterite is ultramafic igneous rock that consists of roughly equal proportions of orthopyroxene and clinopyroxene. It is a type of pyroxenite.
Can olivine and quartz be in the same rock?
Olivine is typically with pyroxenes (in basalt, for example) and quartz + K-feldspar with micas (biotite and muscovite) is a typical composition of granite. But there are no such rock types that are composed of olivine plus quartz.
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).
What are the four types of igneous intrusions?
Igneous Intrusions
- Sills: form when magma intrudes between the rock layers, forming a horizontal or gently-dipping sheet of igneous rock.
- Dykes: form as magma pushes up towards the surface through cracks in the rock.
- Batholiths:
Is peridotite a Subhedral?
Coarse peridotite The coarse texture derives from early crystallization of subhedral, large olivine (3–10 mm) and orthopyroxene (0.8–5 mm) and late crystallization of anhedral clinopyroxene (1–7 mm), garnet and spinel (Fig. 2a).
What is Allotriomorphic texture?
(iii) Allotriomorphic texture: When most of the crystals are anhedral, the texture is called “allotriomorphic”. The crystals of these fine grained rocks are commonly anhedral or subhedral, they are called microgranular texture.