ERS 103 ch 6

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Greenschist

(1) A low-grade metamorphic rock formed from mafic volcanic rock and containing abundant chlorite (2) The metamorphic grade above the zeolite grade

contact metamorphism

A change in the texture, structure, or chemical composition of a rock due to contact with magma.

zeolite

A natural or synthesized silicate used to soften water.

eclogites

Metamorphic Facies moderate temperatures, high pressures

greenschist facies

Metamorphic conditions typified by low temperature and low pressure.

amphibolite facies

The metamorphic facies at which hornblende becomes stable; characterized by coarse-grained schists and amphibolites formed under conditions of medium temperature and pressure.

eclogite facies

The metamorphic facies at which rocks containing garnet and omphacite become stable; rocks in this facies are usually unfoliated and form under conditions of extremely high pressure and moderate temperature; usually associated with subduction zones.

granulite facies

The metamorphic facies in which gneisses become common; rocks in this facies are usually foliated and consist of minerals that form under conditions of high temperature and pressure.

Foliation

The metamorphic rock texture in which mineral grains are arranged in planes or bands.

melange

a mixture; medley.

Foliation is caused by:

confining pressure

Zeolites

natural crystalline minerals or synthetic materials consisting of three-dimensional networks of channels that contain sodium or other 1+ cations

granoblastic texture

no foliation

Quartzite (Metamorphic)

non-foliated

Amphibolite

nonfoliated metamorphic rock; metamorphism of mafic rocks (basalt and gabbro) can't produce quartz and muscovite when metamorphosed, for these rocks don't contain the right mix of chemicals to yield such minerals. They transform into this dark-colored rock containing hornblende and plagioclase.

granoblastic rocks

nonfoliated metamorphic rocks composed mainly of crystals that grow in equant shapes

Burial metamorphism produces

nonfoliated rocks only

seafloor metamorphism

occurs at mid-ocean ridges, where intruding magma drives seawater circulation through extruded basalts

Regional metamorphism occurs

over large areas and is associated with mountain building

Greenstone Belts

zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies

Amphibolite

(1) A usually granoblastic rock made up mainly of amphibole and plagioclase feldspar, typically formed by medium- to high-grade metamorphism of mafic volcanic rock Foliated amphibolites can be produced by deformation (2) The metamorphic grade above greenschist

hornfels facies

-High increase of temperature due to contact metamorphism -The mineralogical composition depends of the parent material

Granulite

1) a high grade, medium to coarse grained granoblastic rock 2) the highest metamorphic grade

regional metamorphism

A change in the texture, structure, or chemical composition of a rock due to changes in temperature and pressure over a large area, generally as a result of tectonic forces.

phyllite

A fine-grained metamorphic rock with a foliation caused by the preferred orientation of very fine-grained mica.

Hornfels

A fine-grained, unfoliated metamorphic rock.

stress

A force that acts on rock to change its shape or volume -confining pressure: general force applied equally in all directions -directed pressure: force exerted in a particular direction

seafloor metamorphism

A form of metasomatism associated with mid-ocean ridges, in which seawater infiltrates hot basaltic lava, is heated, circulates through the newly forming oceanic crust by convection, and reacts with and alters the chemical composition of the basalt

metamorphic facies

A group of associated minerals that are used to establish the pressures and temperatures at which rocks undergo metamorphism.

granulite facies

A high grade of metamorphism producing medium- to coarse-grained rocks that lack hydrous minerals like biotite and amphibole.

Zeolites

A large group of hydroaluminosilicate minerals that are analogous in composition to the feldspars. Chief metals are Na, Ca, and K. They occur in basalt cavities, saline lake and deep sea sediments, and volcanic tuff. They are used as water softeners or desiccants.

Greenstone

A low-grade granoblastic rock produced by the metamorphism of mafic volcanic rock and containing abundant chlorite, which accounts for its greenish cast

Granulite

A medium- to coarse-grained granoblastic rock formed under conditions of relatively high pressure and temperature.

zeolite facies

A metamorphic facies formed at relatively low temperature and pressure where zeolite minerals are stable.

quartzite

A metamorphic rock formed from sandstone.

Blueschist

A metamorphic rock formed under conditions of high pressure and moderate temperature, often containing glaucophane, a blue amphibole.

Eclogite

A metamorphic rock formed under very high pressure and moderate to high temperature, typically containing minerals such as coesite (a very dense, high-pressure form of quartz).

foliated rocks

A metamorphic rock that has mineral grains which line up in parallel layers

Migmatite

A rock exhibiting both igneous and metamorphic rock characteristics. Such rocks may form when light-colored silicate minerals melt and then crystallize, while the dark silicate minerals remain solid.

Migmatite

A 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.

Greenschist

A schist containing chlorite and epidote (which are green) and formed by low-pressure, low-temperature metamorphism of mafic rocks.

metamorphic facies

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

gneissic texture

A texture of metamorphic rocks in which dark and light silicate minerals are separated, giving the rock a banded appearance.

porphyroblastic texture

A texture of metamorphic rocks in which particularly large grains (porphyroblasts) are surrounded by a fine-grained matrix of other minerals.

slate

A type of Metamorphic rock that was once shale rock formed by heat and pressure.

Foliation

An arrangement of minerals in flat or wavy parallel bands.

Eclogite

An ultra-high-pressure metamorphic rock formed at the base of the crust at moderate to high temperatures, typically containing minerals such as coesite (a very dense, high-pressure form of quartz)

Granoblastic

Describes the texture of metamorphic rocks that contain interlocking equi-dimensional crystals.

Gneissic

Distinctive banded appearance, high-grade metamorphism

gneissic texture

During high-grade metamorphism, ion migration results in the segregation of minerals into light and dark bands

Gneissic

During higher grades of metamorphism, ion migration results in the segregation of minerals Gneissic rocks exhibit a distinctive banded appearance

slate

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

Phyllite (foliated)

Gradation in the degree of metamorphism between slate and schist; Platy minerals not large enough to be identified with the unaided eye; Glossy sheen and wavy surfaces Exhibits rock cleavage; Composed mainly of fine crystals of muscovite and/or chlorite

Greenstone

Green colored metamorphic rocks formed from dark igneous rocks that often occur in belts within Precambrian shields.

high-pressure metamorphism

High pressure metamorphism is one that occurs at high pressure (8-12 kbar) and ultra-high pressure (greater than 28 kbar)

Metamorphic Facies and Plate Tectonics

High-pressure, low-temperature metamorphism is associated with the upper section of subduction zones

Porphyroblasts

In metamorphic rock, the larger crystals set in a finer-grained matrix are called ______________

Greenschist

Low grade; pronounced foliation; green color from chlorite

Gneiss

Metamorphic, Foliated

schist

Metamorphic, Foliated

seafloor metamorphism

Metamorphism associated with mid-ocean ridges, in which changes in a rock's bulk chemical composition are produced by fluid transport of chemical components into or out of the rock.

Metasomatism

Metamorphism coupled with the introduction of ions from an external source.

ultra-high-pressure metamorphism

Metamorphism occurring at pressures greater than 28 kbar

high-pressure metamorphism

Metamorphism occurring at pressures of 8 to 12 kbar

shock metamorphism

Metamorphism that occurs when minerals are subjected to high pressures and temperatures by heat and shock waves generated when a meteorite collides with Earth

Migmatite

Mixed igneous and metamorphic rock.

Contact metamorphism occurs when

Molten rock partially melts the rock around it

hornfels

Rock that undergoes metamorphism simply because of a change in temperature, without being subjected to differential stress.

shock metamorphism

Solid-state changes in rock that result from the extreme pressure accompanying a meteorite impact.

P-T path

The history of changing temperature (T) and pressure (P) conditions that is reflected in the texture and mineralogy of a metamorphic rock

greenschist facies

The most common metamorphic facies characterized by a variety of green minerals; rocks in this facies are usually foliated and form under conditions of low temperatures and pressures.

exhumation

The process (involving uplift and erosion) that returns deeply buried rocks to the surface.

Granoblastic

The texture found in metamorphic rocks that contain interlocking equidimensional crystals

Gneissic

The texture of a metamorphic rock in which minerals are separated into light and dark layers or lenses.

quartzite and marble

Two common metamorphic rocks that typically lack foliation are ____________.

porphyroblastic texture

Unusually large grains, called porphyroblasts, are surrounded by a fine-grained matrix of other minerals

gneissic texture

What kind of metamorphic texture results in the segregation of light and dark mineral bands?

blueschist facies

Which of the following metamorphic rocks is most likely to be formed at the oceanic trench where an oceanic crust is being subducted underneath another plate

Granoblastic

a "mosaic" of uniformed sized, equidimensional grains. Common in sub-monomineralic rocks (quartz & calcite)

Phyllite

a foliated rock that is intermediate in metamorphic grade between slate and schist, containing small crystals of mica and chlorite that give it more or less glossy sheen.

Greenschist/Greenstone

a low grade metamorphic rock that typically contains chlorite, actinolite, epidote, and albite

Contact metamorphism occurs when

a mass of rock is affected by the heat of a magma.

Quartzite

a metamorphic rock composed of quartz and transformed from a protolith of quartz sandstone

blueschist

a relatively rare metamorphic rock that contains an unsual blue-colored amphibole called glaucophane. Occurs only in the accretionary prisms that form at subduction zones. Because of shear between the subducting plate and the overriding plate, foliation develops.

Porphyroblastic

a small number of very large minerals

high-pressure metamorphism

along linear belts of volcanic arcs, produced by continent-continent collision, occurs at high pressures

Metamorphism

alteration in the minerology, texture, or chemical composition of solid rock

porphyroblastic texture

an arrangement of large crystals, called porphyroblasts, set in a finer grained groundmass

Greenstone Belts

ancient plate boundaries, sequence of igneous, metamorphic, sedimentary rocks; associated with formation of continents; source of economically important minerals

hornfels facies

associated with contact metamorphism

Metasomatism

change in the composition of a rock by fluid transport of chemical substances into or out of the rock

contact metamorphism

changes in rock caused by the heat from a nearby magma body

zeolite facies

characterized by zeolite, especially laumonite, wairakite, analcime

foliated rocks

contain parallel layers of flat and elongated minerals

Regional metamorphism occurs

convergent plate boundaries

Foliation in metamorphic rocks results from:

directed or dynamic pressure

Foliation is caused by:

directed pressure

how are metamorphic rocks related to plate tectonics?

during subduction and continent-continent collision at convergent plate boundaries, rock and sediments are pushed to great depths in earth's crust, where they are subjected to increasing pressures and temperatures that result in metamorphism.

quartzite and marble

examples of non-foliated metamorphic rocks

Kinds of metamorphic rocks

foliated granoblastic

regional metamorphism

form at convergent plate boundaries. occurs at moderate to deep levels under moderate to ultra-high pressures and high temperatures

granoblastic texture

form during recrystallization, crystals of roughly same size, exhibit polygonal grain boundaries

contact metamorphism

formation of a metamorphic rock caused by magma coming into contact with existing rock

regional metamorphism

formation of metamorphic rock bodies that are hundreds of square kilometers in size

blueschist facies

glaucophane, lawsonite, epidote

metamorphic facies

groupings of metamorphic rocks of various mineral compositions formed under different grades of metamorphism from different parent rocks

blueschist metamorphism

high pressure-low temperature metamorphism which occurs only in subduction zones along active convergent plate boundaries

causes of metamorphism

increases in pressure and temperature reactions with chemical components introduced by hydrothermal solutions

Porphyroblast

large crystals that form in solid rock by the reorganization of atoms during metamorphism

Porphyroblasts

large crystals that form in solid rock by the reorganization of atoms during metamorphism

Porphyroblastic

large grains surrounded by fine grained matrix of other minerals

foliated rocks have

layers

Foliated rocks are distinguished by ____.

layers and bands of crystals

Foliation is caused by:

lithostatic pressure

burial metamorphism

low-grade metamorphism that occurs in the lowest layers of very thick accumulations of sedimentary strata

A migmatite is a mixed ___ rock.

metamorphic and igneous

A migmatite is a rock that is in a stage between

metamorphic and igneous rocks

marble

metamorphic rock that was once limestone

foliated rocks

metamorphic rocks with crystals arranged in parallel layers or bands

regional metamorphism

metamorphism associated with large-scale mountain-building processes

burial metamorphism

metamorphism due only to the consequences of very deep burial

Shock metamorphism can occur as a result of ______.

meteorite impact

Shock metamorphism results from:

meteorite impact

Contact metamorphism occurs when

molten rock comes in contact with other rocks

Granulite Association

primarily gneisses representing metamorphosed and deformed tonalites, graniodiorites, and granites

types of metamorphism

regional contact seafloor burial high pressure, ultra-high pressure shock

burial metamorphism

results from the burial of rocks in a sedimentary basin (river basin)

Greenstone Association

synclinal belts of metavolcanic and metsedimentary rocks

shock metamorphism

the changes that can occur in a rock due to the passage of a shock wave, generally resulting from a meteorite impact

exhumation

the overall process by which deeply buried rocks end up back at the surface

Metasomatism

the process by which a rock's overall chemical composition changes during metamorphism because of reactions with hot water that bring in or remove minerals (copper, zinc, lead, metallic ores)

Foliation

the process of being split into thin sheets or laminae.

exhumation

the transportation of subducted metamorphic rocks back to Earth's surface

amphibolite facies

this metamorphic facies develops deeper in orogenic belts with high temps and moderate to high pressures, form higher grade metamorphic rocks such as schist, gneiss, quartzite, and marble

granulite facies

this metamorphic facies develops in deep regional metamorphism with very high temp and pressures, forms highest grade metamorphic rocks

blueschist facies

this metamorphic facies develops in subduction zones at low temperatures and high pressures

eclogite facies

this metamorphic facies develops in tectonic blocks and shear zones under very high pressures and are rare except in California

greenschist facies

this metamorphic facies develops under regional metamorphism with moderate temp and pressures, form low-grade metamorphic rocks such as slate, phyllite

Greenstone Belts

zones of metamorphic rocks that occur within Archean rock

what do metamorphic rocks reveal about the conditions under which they were formed?

zones of metamorphism can be mapped with isograds defined by the first appearance of an index mineral.


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