Metamorphic rocks Flashcards
It’s a process involving changes in the mineral content/ composition and microstructure of a rock that is dominantly in the solid state.
Metamorphism
Type of metamorphism that occurs an area of wide extent, that is, affecting large rock volume. This process is usually associated with ocean-floor spreading, crustal thickening related to plate collision, deep basin subsidence.
Regional metamorphism
Type of metamorphism that is directly attributed to a localized cause such as a magmatic intrusion, faulting, or meteorite impact.
Local metamorphism
Type of metamorphism of regional extent. It is associated with various phases of orogenic development and involves both compressional and extensional regimes.
Orogenic metamorphism
Type of metamorphism mostly with regional extent. Affects rocks deeply buried under a sedimentary-volcanic pile and is typically not associated with deformation or magmatism. Lack of schistosity.
Burial metamorphism
Type of metamorphism of regional or local extent related to the steep geothermal gradient occurring near spreading centers in the oceanic environment. Associated with circulating hot aqueous fluids.
Ocean-floor metamorphism
Type of metamorphism of local extent, associated with fault zones or shear zones. Grain size reduction typically occurs commonly referred to as mylonites and cataclasites.
Dislocation metamorphism
Type of metamorphism of local extent caused by the passage of a shock wave. Includes melting and vaporization of the target rocks.
Impact metamorphism
Type of metamorphism of a local extent that affects the country rock around magma bodies emplaced in a variety of environments from volcanic to upper mantle depths.
Contact metamorphism
Type of contact metamorphism characterized by very high temperatures, at a very low pressure generated by a volcanic or subvolcanic body. Form fritted rocks and buchites)
Pyrometamorphism
Type of metamorphism of local extent caused by hot H2O-rich fluids. Metasomatism is commonly associated with this type of metamorphism.
Hydrothermal metamorphism
Type of metamorphism of local extent produced by the spontaneous combustion of naturally occurring substances such as bituminous rocks, coal, or oil. The resulting rock is commonly a fulgurite, an almost entirely glassy rock.
Combustion metamorphism
As the pressure and temperature increase, a rock of a given chemical composition is expected to undergo a continuous series of chemical reactions between its constituents minerals and any fluid phase present to produce a series of new mineral assemblages that are stable at the higher pressures and temperatures.
Prograde
Metamorphism gives rise to the formation of minerals that are typical of a lower grade.
Retrograde
Surface across the rock sequence, represented by a line on a map, defined by the appearance of disappearance of a mineral, a specific mineral composition or a mineral association.
Isograd
The concept of metamorphic facies was first proposed by ___________.
Eskola (1915)
Refers to the original rock, prior to metamorphism
Protolith
These rocks are derivatives of aluminous sedimentary rocks like shales and mudrocks.
Pelitic
Rocks that originally contained mostly quartz and feldspar like granitic rock and arkosic sandstone, will also contain an abundance of quartz and feldspar as metamorphic rocks, since these minerals are stable of a wide range of temperature and pressure.
Quartzo-Feldspathic
Derivatives of carbonate rocks, although they contain other minerals that result from the reaction of the carbonates with associated siliceous detrital minerals that were present in the rock.
Calcareous
At low-grade of metamorphism calcareous rocks are recognized by their abundance of carbonate minerals like _________ and _________.
Calcite and dolomite
The increasing metamorphic grade of calcareous rock are replaced by minerals like _____, ____, ____, and _____.
brucite, phlogopite, chlorite, and tremolite
At even higher temperatures the calcareous mineral will turn into ____, ____, ____, ____, and ____.
diopside, forsterite, wollastonite, grossularite, and calcic plagioclase.
Derivatives of rocks like basalts and gabbros.
Basic/ Ultrabasic
Rocks that could be a derivative of iron-rich cherts and ironstone. Contains little Mg
Ferriginous
Defined by the occurrence of zeolites in mafic rocks, but not identifiable in metapelites.
Zeolite facies
Defined by the occurrence of prehnite and pumpellyite in metabasites. Defined by the occurrence of illite, chlorite and smectite in metapelites.
Prehnite-pumpellyite facies
Defined by the occurrence of pumpellyite + actinolite in mafic rocks.
Pumpellyite-Actinolite facies
Defined by the occurrence of prehnite + actinolite in mafic rocks.
Prehnite -Actinolite facies
Defined by the occurrence of lawsonite + albite + chlorite +/- pumpellyite or actinolite or glaucophane in mafic rocks. Defined by the occurrence of carpholite + chlorite or phengite + paragonite in metapelites.
Lawsonite-albite subfacies/Lawsonite blueschist subfacies
Defined by the occurrence of glaucophane + epidotes + garnet/chlorite + phengite +/- actinolite in metabasites. Defined by the occurrence of chloritoid + paragonite + chlorite + phengite in metapelites. Characterized by the lack of biotite in metasediments and metabasites (phengite instead of Bt).
Epidote-blueschist subfacies
Defined by the occurrence of garnet + omphacite in mafic rocks. No albite (epidote or grossular garnet are the stable Ca Al silicates). Defined by the occurrence of talc + kyanite + phengite +/- yoderite in metapelites.
Eclogite facies
Eclogites that form in the mantle and are brought up to the surface with kimberlites in diatremes. Garnets in these eclogites are rich in pyrope.
Type A. Eclogite facies
Eclogites that form in the lower crust and are associated with gneiss terrains (granulites and high grade amphibolites). Garnets in this group are rich in grossular and almandine.
Type B. Eclogite facies
Eclogites that form at relatively low temperatures in what are now known as subduction zones. These eclogites contain almandine rich garnet and are associated with blueschists.
Type C. Eclogite facies
Defined by the occurrence of actinolite + chlorite + albite +/ epidote in mafic rocks. Defined by the occurrence of chlorite + albite + biotite + muscovite +/- andalusite/kyanite +/- chloritoid in metapelites.
Greenschist facies
Defined by the occurrence of epidote + amphibole (actinolite/hornblende) + plagioclase +/- chlorite/garnet in mafic rocks. Defined by the occurrence of biotite + garnet (almandine) + plagioclase + chlorite + muscovite +/- chloritoid in metapelites.
Epidote amphibolite facies
Defined by the occurrence of amphibole (hornblende) + plagioclase (andesine) +/- garnet +/- epidote +/- diopside in mafic rocks. Defined by the occurrence of garnet + staurolite + muscovite + biotite +/ andalusite/kyanite/sillimanite in metapelites.
Amphibolite facies
Defined by the occurrence of plagioclase + hypersthene + diopside + garnet + spinel in mafic rocks. Defined by the occurrence of perthite + plagioclase + sillimanite + garnet +/- hypersthene in metapelites. cordierite + garnet are characteristic of low P granulites.
Granulite facies
Defined by the occurrence of plagioclase + hypersthene + augite + tridymite in mafic rocks. Defined by the occurrence of sanidine + Cordierite + spinel + hypersthene + sillimanite in metapelites.
Sanidinite facies
*100-200 degrees Celsius
Pelitic - interlayered smectite/ chlorite calcite
Calcareous - calcite
Mafic - Laumonite, thompsonite, calcite, interlayered smectite/ chlorite
Zeolite facies
*150-300 degrees Celsius
Pelitic - prehnite, pumpellyite, calcite, chlorite, albite
Calcareous - calcite
Mafic - prehnite, pumpellyite, calcite, chlorite, albite
Prehnite-pumpellyite
*300-450 degrees Celsius
Pelitic - muscovite, chlorite, quartz, albite, biotite, garnet
Calcareous - calcite, dolomite, quartz, epidote, tremolite.
Mafic - albite, chlorite, quartz, epidote, actinolite, sphene
Greenschist
*450-550 degrees Celsius
Pelitic - muscovite, biotite, garnet, albite, quartz
Calcareous - calcite, quartz, tremolite, epidote, diopside
Mafic - albite, epidote, hornblende, quartz
Epidote Amphibolite
*500-700 degrees Celsius
Pelitic - garnet, biotite, muscovite, quartz, plag, staurolite, kyanite, sillimanite
Calcareous - calcite, diopside, quartz, wollastonite
Mafic - hornblende, plag, garnet, quartz, sphene, biotite
Amphibolite
*700-900 degrees Celsius
Pelitic - garnet, Kspar, sillimanite or kyanite, quartz, plag, hypersthene.
Calcareous - calcite, quartz, plag, diopside, hypersthene
Mafic - plagioclase, augite, hypersthene, hornblende, garnet, olivine
Granulite
*150 - 350 degrees Celsius
P> 5-8Kb
Pelitic - jadeite, albite, quartz, lawsonite, aragonite, paragonite
Calcareous - aragonite, white mica
Mafic - glaucophane, albite, lawsonite, sphene, garnet
Blueschist
*350-750 degrees Celsius
P>8-10 Kb
Pelitic - coesite, kspar, sillimanite, plagioclase
Calcareous - aragonite, quartz, plag, diopside, hypersthene
Mafic - omphacite (px), pyrope garnet
Eclogite
