Geology ch. 8 Metamorphic Rocks

Ecologite

very high-grade metamorphic rock, made up of mostly garnet and pyroxene, lacks water bearing minerals, and form deep within subduction zones. Form even deeper than blueschists. Basalt protolith.

they are smashed

while closer to the Earth's surface the rocks tend to break in a brittle fashion.

Agents of metamorphism

1.) Heat 2.) Pressure and Stress 3.) Chemically active fluids

Schists

A medium-to-coarse-grained schistose foliated metamorphic rock that possesses schistosity. At higher temperatures and pressures than slate and phyllite.

mylonites

A metamorphic rock type that is produced as a result of dynamic metamorphism are.... (Fine-grained rock formed by the nonbrittle subdivision of larger grains).

Marble

A nonfoliated metamorphic rock composed of calcite and transformed from a protolith of limestone.

Anthracite coal

A nonfoliated metamorphic rock composed of carbon and transformed from a protolith of bituminous coal.

Quartzite

A nonfoliated metamorphic rock composed of quartz and transformed from a protolith of quartz sandstone.

Shear stress

A stress that moves one part of a material sideways past another part.

they are stretched

At depth the deformation in fault zones tends to behave in a more plastic fashion.

Chemically active fluids

Dissolved elements in hot fluids will react chemically to change the minerals in a rock.

Slate

Fine-grained, slaty foliated low-grade metamorphic rock, formed by the metamorphism of shale.

Schistosity

Foliation caused by the preferred orientation of large mica flakes.

foliated

Layering formed as a consequence of the alignment of mineral grains, or of compositional banding in a metamorphic rock.

Regional metamorphism

Metamorphism that involves heat, pressure, and shearing. This type of metamorphism is the result of collisions of one tectonic plate with another tectonic plate.

dynamic metamorphism

Metamorphism that occurs as a consequence of shearing alone, with no change in temperature or pressure.

nonfoliated

Rock containing minerals that recrystallized during metamorphism, but which has no layering has appeared.

metasomatism

This process by which a metamorphic rock's chemical composition changes due to the interaction with hydrothermal fluids is called.

Blueschist

is a rock that forms by the metamorphism of basalt at high pressures and low temperatures within subduction zones. The blue color of the rock comes from blue colored minerals within the rock.

Greenstone

metamorphic rock produced by hydrothermal alteration. The green color come from the new metamorphic minerals (epidote, chlorite, etc..) formed as hot water interacted with the rock.

Hornfels

metamorphic rocks formed by contact metamorphism. The high heat of the magma "baked" the rock (not unlike clay in a kiln).

Amphibolite

nonfoliated metamorphic mafic rocks that consists of the minerals hornblende and plagioclase. These rocks were basalts and gabbros before they were deformed.

Protolith

preexisting rock that was deformed and modified into a metamorphic rock. (parent rock)

Phase change

to change one mineral into a different mineral

The settings of metamorphism

1) Contact or thermal metamorphism 2) Hydrothermal metamorphism 3) Regional metamorphism 4) Dynamic metamorphism 5) Burial metamorphism:

What are the two kinds of differential stress

1.) Normal Stress 2.) Shear Stress

Formation of a metamorphic rock (steps)

1.) Recrystallization 2.) Phase change 3.) Metamorphic reaction 4.) Plastic deformation

Migmatite

A compositional banded foliated metamorphic rock formed when gneiss is heated high enough so that it begins to partially melt, creating layers, or lenses, of new igneous rock that mix with layers of the relict gneiss. Formed at the highest temperatures and pressures of any foliated metamorphic rock.

Gneiss

A compositionally banded compositional banded foliated metamorphic rock typically composed of alternating dark- and light-colored layers. Formed at higher temperatures and pressures than slate, phyllite, and schists. Usually formed from the melting of a protolith.

Phyllite

A fine-grained slaty foliated metamorphic rock. The foliation is caused by the preferred orientation of very fine-grained mica. Forms at higher temperatures and pressures than slate.

metamorphic facies

A set of metamorphic mineral assemblages indicative of metamorphism under a specific range of pressures and temperatures.

Compositional banding

A type of metamorphic foliation, found in gneiss, defined by alternating bands of light and dark minerals.

burial metamorphism

As more rocks form on top of each other, rocks become buried deeper into the earth.

blueschist metamorphism

In subduction zones pressure become very high because of the collision of 2 tectonic plates; however, the temperature can stay relatively low because of all of the water. This is called....

hydrothermal fluids

Metamorphic reactions usually take place in the presence of very hot fluid. These fluids react chemically with the rocks during metamorphism.

spinel type structure

Phase change occurs at depth in the earth when the mineral olivine converts into a different mineral structure called a....

Slaty cleavage

The foliation typical of slate, and reflective of the preferred orientation of slate's clay minerals, that allows slate to be split into thin sheets.

Metamorphism

The process by which one kind of rock transforms into a different kind of rock.

Normal stress

The push or pull that is perpendicular to a surface.

Aureole

The region around a pluton, stretching tens to hundreds of meters out, in which heat transferred into the country rock and metamorphosed it.

Rock cycle

The succession of events that results in the transformation of Earth materials from one rock type to another, then another, and so on.

Hydrothermal metamorphism

When cold sea water interacts with the hot rising magma at mid-ocean ridges, the sea water heats up and produces a metamorphism that is rich in Iron.

Differential stress

a condition causing a material to experience a push or pull in one direction of a greater magnitude than the push or pull in another direction; in some cases, differential stress can result in shearing.

Metamorphic rocks

a rock that forms from the modification of another rock.

Sedimentary rocks

can consists of fragments derived from older metamorphic, igneous and sedimentary rocks.

Igneous rocks

can form from the partial melting of older sedimentary, metamorphic and igneous rocks.

Metamorphic rocks

can form through the deformation of older sedimentary, igneous and metamorphic rocks.

Contact Metamorphism

caused by heat conducted into country rock from an igneous intrusion.

Plastic deformation

deformational process in which mineral grains behave like plastic and, when compressed or sheared, become flattened or elongate without cracking or breaking.

Metamorphic reaction

growth of new minerals out of the protolith due to metamorphic processes. This is a type of diffuse mineral growth.

Heat

increases with depth. Can cause a rock to recrystallize, grow new minerals that are not stable at lower temperatures, and can cause a rock to melt.

Pressure and Stress

increases with depth. Confining pressure can cause a rock to become more compact. Differential stress will deform a rock in one direction greater than another.

Recrystallization

to change the shape and size of a mineral without changing its original composition.