What Causes Foliated Metamorphic Textures


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What Causes Foliated Metamorphic Textures?

Metamorphic textures

Foliation is caused by the re-alignment of minerals when they are subjected to high pressure and temperature. Individual minerals align themselves perpendicular to the stress field such that their long axes are in the direction of these planes (which may look like the cleavage planes of minerals).

What causes foliated metamorphic textures to form?

Foliated Metamorphic Rocks:

Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned. These rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied.

What causes a foliated texture?

Foliation is produced in a rock by the parallel alignment of platy minerals (e.g. muscovite biotite chlorite) needle-like minerals (e.g. hornblende) or tabular minerals (e.g. feldspars). This parallel alignment causes the rock to split easily into thin layers or sheets.

What is the main cause of foliation?

Foliation in geology refers to repetitive layering in metamorphic rocks. … It is caused by shearing forces (pressures pushing different sections of the rock in different directions) or differential pressure (higher pressure from one direction than in others).

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What type of metamorphism causes foliation?

Most regional metamorphism is accompanied by deformation under non-hydrostatic or differential stress conditions. Thus regional metamorphism usually results in forming metamorphic rocks that are strongly foliated such as slates schists and gniesses.

What causes regional metamorphism?

Regional metamorphism is caused by large geologic processes such as mountain-building. These rocks when exposed to the surface show the unbelievable pressure that cause the rocks to be bent and broken by the mountain building process. Regional metamorphism usually produces foliated rocks such as gneiss and schist.

What is the main factor that affects regional metamorphism?

Temperature hydrostatic pressure and shearing stress together with the chemical activity of percolating pore fluids are the major physical variables governing the process of regional metamorphism.

What does it mean when a metamorphic rock has foliation quizlet?

What does it mean when a metamorphic rock has foliation? Mineral grains are aligned in layers by pressure.

What does foliated texture describe?

Foliation is a term used that describes minerals lined up in planes. Certain minerals most notably the mica group are mostly thin and planar by default. Foliated rocks typically appear as if the minerals are stacked like pages of a book thus the use of the term ‘folia’ like a leaf.

What are foliated textures?

Foliation is described as the existence or appearance of layers. Foliated textures result from a parallel arrangement of flat platy minerals. This is usually a result of mineral recrystallization in the presence of a directed pressure. … Very flat foliation that resembles mineral cleavage.

How does differential stress lead to foliation texture?

Cause of Foliation

All rocks are under pressure as a result of burial. This confining pressure increases in proportion to the depth of burial. … This means that differential stress related to different pressure in different directions is required to form foliated metamorphic rocks.

What type of stress would cause foliation?

Most foliation is caused by the preferred orientation of phylosilicates like clay minerals micas and chlorite. Preferred orientation develops as a result of non-hydrostatic or differential stress acting on the rock (also called deviatoric stress).

What geologic conditions and forces cause metamorphism?

Metamorphism occurs because some minerals are stable only under certain conditions of pressure and temperature. When pressure and temperature change chemical reactions occur to cause the minerals in the rock to change to an assemblage that is stable at the new pressure and temperature conditions.

How will foliation in continental metamorphic rocks formed during subduction be oriented?

Pre-existing rock is altered through heat and pressure. … How will foliation in continental metamorphic rocks formed during subduction be oriented? Perpendicular to the direction of plate movement.

Where does regional metamorphism occur?

As described above regional metamorphism occurs when rocks are buried deep in the crust. This is commonly associated with convergent plate boundaries and the formation of mountain ranges. Because burial to 10 km to 20 km is required the areas affected tend to be large.

What rock is formed by regional metamorphism?

Most foliated metamorphic rocks—slate phyllite schist and gneiss—are formed during regional metamorphism. As the rocks become heated at depth in the Earth during regional metamorphism they become ductile which means they are relatively soft even though they are still solid.

What is foliated metamorphism?

Foliated metamorphic rocks have a layered or banded appearance that is produced by exposure to heat and directed pressure. Examples of foliated rocks include: gneiss phyllite schist and slate. Non-foliated metamorphic rocks do not have a layered or banded appearance.

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What causes regional metamorphism quizlet?

What causes regional metamorphism? Pressure builds up in rock that is buried deep below other rock formations or when large pieces of the Earth’s crust collide with each other.

Is a common foliated metamorphic rock quizlet?

Slate schist and gneiss (pronounced ‘nice’) are all foliated metamorphic rocks.

What are the four factors that determine the texture and mineral content of a metamorphic rock?

The Factors That Control Metamorphic Processes
  • The mineral composition of the parent rock.
  • The temperature at which metamorphism takes place.
  • The amount and type (direction) of pressure during metamorphism.
  • The amount and type of fluid (mostly water) that is present during metamorphism.

How are minerals affected by regional metamorphism?

When carbonate sediments are subjected to thermal or regional metamorphism the CO2 cannot often escape and the carbonate minerals simply recrystallize calcite and dolomite commonly form marble. Carbonate minerals can therefore be common in some metamorphic rocks.

What causes contact metamorphism?

Contact metamorphism occurs due to heating with or without burial of rocks that lie close to a magma intrusion. It is characterized by low P/T gradients as strong thermal gradients between an intruding magma and adjacent country rock are best established at shallow crustal levels.

What are the characteristics of a foliated metamorphic rock quizlet?

Foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains.

What does it mean to be foliated quizlet?

Foliated means that the minerals in a metamorphic rock are aligned in sheets or bands (like stripes if colors contrast)

What is foliation geology quizlet?

What is foliation? The planar (nearly flat) arrangement of mineral grains or crystals within a rock.

What kind of force creates foliation in metamorphic rocks?

Foliation normally forms when pressure was exerted on a rock from one direction. If pressure is exerted from all directions then the rock usually does not show foliation. There are two main types of metamorphism: Contact metamorphism—occurs when magma contacts a rock changing it by extreme heat (Figure 4.14).

How a metamorphic rock could develop a foliated appearance or a Nonfoliated appearance?

Nonfoliated = metamorphic rocks that are formed under high temperature and LOW PRESSURE. Foliated metamorphic rocks are formed within the Earth’s interior under extremely high pressures that are unequal occurring when the pressure is greater in one direction than in the others (directed pressure).

Which metamorphic facies is associated with subduction zones?

Blueschist-facies metamorphism is important in subduction zones where high-pressure relatively low-temperature mineral assemblages form.

What does metamorphic texture describe?

Metamorphic texture is the description of the shape and orientation of mineral grains in a metamorphic rock. Metamorphic rock textures are foliated non-foliated or lineated are described below.

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Where do most metamorphic rocks form quizlet?

Most metamorphic rocks form deep underground. They form under extreme heat and pressure. This is any process that affects the structure or composition of a rock in a solid state as a result of changes in temperature pressure or the addition of chemical fluids.

What is non-foliated metamorphic rocks?

Overview. Nonfoliated metamorphic rocks lack foliated texture because they often lack platy minerals such as micas. They commonly result from contact or regional metamorphism. Examples include marble quartzite greenstone hornfel and anthracite.

What are two reasons a metamorphic rock might not show foliation?

There are two main types of metamorphic rocks: those that are foliated because they have formed in an environment with either directed pressure or shear stress and those that are not foliated because they have formed in an environment without directed pressure or relatively near the surface with very little pressure

What type of pressure will result in a foliated texture?

Differential stress (pressure) is the main force causing minerals to align parallel to each other and create a texture that is foliated or lineated. Correct! Differential stress (pressure) is the main force causing minerals to align parallel to each other and create a texture that is foliated or lineated. 4.

What force causes folding?

(a) Fig. 10.6a: Compressive forces generate folding and faulting as a consequence of shortening. Compressive forces are common along convergent plate boundaries resulting in mountain ranges.

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