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General Metamorphic Terms
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- 1Thermal metmorphismMetamorphism due to a change in temperature producing new minerals, grain growth and, in general, equilibrium textures.
- 2Contact metamorphismMetamorphism in the wall rock surrounding an igneous intrusion. Predominantly thermal metamorphism with or without metasomatism.
- 3Regional metamorphismMetamorphism occurring on a regional scale (100s to 1000kms) generally associated with orogenic belts. Simultaneous changes in pressure and temperature, often accompanied by deformation.
- 4Dislocation metamorphismMetamorphism occurring along in fault zones. Commonly involves intense deformation (brittle and ductile).
- 5MetasomatismA process producing a significant change in chemical composition of the system, usually due to flow of large quantities of a fluid through the rock.
- 6Metamorphic gradeAn indication of the temperature conditions under which the metamorphism occurred as inferred from the mineralogy of the rocks. Low grade is characterised by hydrated or carbonated phases and higher-grade assemblages are more anhydrous and CO2 poor. Metamorphic grade is typically used in a relative sense.
- 7Prograde metamorphismMetamorphism under conditions of increasing temperature.
- 8Retrograde metamorphismMetamorphism, generally with decreasing temperature and generally involving hydration and carbonation reactions, which produced minerals which are typically of lower grade than one displayed by the former phase assemblage.
- 9Peak of metamorphismThe part of the metamorphic history at which temperatures reaches a maximum.
- 10PolymetamorphismRepeated episodes of heating with or without deformation.
- 11Mineral assemblageMinerals present in the rock but not necessarily all formed at the same time. This could include secondary alteration minerals.
- 12Mineral paragenesisGroup of minerals in stable or metastable coexistence during a metamorphic event.
- 13Peak-metamorphic paragenesisThe set of minerals in equilibrium together in a rock at the thermal peak of metamorphism.
- 14Metamorphic faciesA set of compatible mineral assemblages which occur in spatially-associated rock types of diverse chemical composition, stable under restricted P-T conditions.
- 15Metamorphic facies seriesSequence of metamorphic facies encountered in a poly-facial suite of rocks along a single traverse across metamorphic terrain.
- 16Metamorphic zoneZones of different minerals marking difference in grade, able to be mapped on a regional scale.
- 17IsogradsLines of equal grade seperating ajacent metamorphic zones. Each isograd is a line, mappable on the ground surface, making the first appearance (proceeding in an up-grade direction) of a particular index mineral. Each isograd represents a metamorphic reaction.
- 18Index mineralA mineral whose first appearance delineates an isograd.
- 19GeothermVerticle depth-temperature (or pressure-temperature) profile through the crust/mantle at any instant time.
- 20P-T pathPath taken by a single rock in P-T space during its metamorphic history (if reliable ages are available for points on this curve, it may be called P-T-t path)
- 21P-T array (Piezothermal Array)Line on a P-T plot representing the locus of P-T conditions recorded by the peak metamorphic parageneses in a poly-facial suite of rocks from a single traverse across a metamorphic terrain (closely related to facies series).
- 22Reaction boundary (Reaction curve)Line on a P-T plot marking the equilibrium position of a univariant mineral reaction. The reactant mineral assemblage is stable on one side of the boundary, and the product mineral assemblages stable on the other side. Some reaction boundaries have been located accurately by laboratory experiments.
- 23Compatability diagramCompositional plots (usually triangular diagram or projection) for a certain type of rock (e.g. pelites) showing stable minerals and minerals assemblage that may exist under a given set of P-T conditions in samples of different bulk composition. Compositions of coexisting minerals in stable equilibrium are joined by 'tie-lines'.
- 24Tie lineStraight line on a compatibility diagram joining compositions of coexisting minerals in a stable equilibrium paragenesis. The arrangement of tie-lines on a compatibility diagram changes on crossing reaction boundary.
- 25Compatible paragenesisParagenesis that can exist at the same P-T conditions. Compatible parageneses have non-crossing tie-lines and non-overlapping tie-lines on a compatibility diagram.
- 26Incompatible paragenesisParagenesis that cannot exist at the same P-T conditions. Incompatible parageneses have crossing tie-lines and overlapping tie-lines and/or overlapping tie-line-triangles on a compatibility diagram.
- 27Retrogenetic gridA P-T plot showing the positions of large set of reaction boundaries relevant to the rocks being studied. Metamorphic facies occupy areas on a petrogenetic grid and are separated from one another by reaction boundaries. If a piexothermic array is drawn on a petrogenetic grid, the facies series is automatically determined.
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- (Keywords) Igneous and Metamorphic Fichas sobre General Metamorphic Terms, creado por Stephen Booth el 24/04/2017.
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- Stephen Booth
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