ERS 103 ch 6
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.