Metamorphic Rocks (Part 1 - Metamorphism and Metamorphic Textures) Flashcards
The process of change or transformation of a pre-existing rock, in the solid state, into another rock due to heat, pressure and chemically active fluids.
Metamorphism
A form of metamorphism due to hydrothermal fluids exchanging constituents with an external source.
Metasomatism
Increase in temperature and pressure
Prograde Metamorphism
Decrease in temperature and pressure
Retrogade Metamorphism
Metamorphism that affects areas with less than 100km²
Local Metamorphism
Metamorphism that affects areas greater than 100km² and is commonly associated with convergent and divergent plate boundaries.
Regional Metamorphism
Also known as Protoliths
Parent Rocks
The original rocks from where the produced metamorphic rocks transformed from.
Protoliths
3 Agents of Metamorphism
Heat
Pressure
Chemically Active Fluids
Provides energy for chemical reactions and recrystallization of minerals.
Heat
Provides stress in equal directions or varying amounts in different directions.
Pressure
Provides and enhances mobility of ions present.
Chemically Active Fluids
Low Temperature Range and Pressure Range
200-300°C , 300-600 MPa; 0-6 km depth
Intermediate Temperature Range and Pressure Range
300-500°C, 600-1000 MPa; 2-20 km depth
High Temperature Range and Pressure Range
> 500°C, >1000 MPa; >20 km depth
2 Types of Pressure
Hydrostatic Pressure
Lithostatic Stress
also called as confining pressure
Hydrostatic Pressure
A uniform or isotropic form of pressure, where pressure is equal in all directions, which usually produces equant grains and non-foliated texture of metamorphic rocks.
Hydrostatic Pressure
also called as burying pressure
Lithostatic Stress
A non-uniform or anisotropic form of pressure, where pressure is unequal in all directions, which usually produces inequant grains and foliated texture of metamorphic rocks.
Lithostatic Stress
6 Types of Metamorphism
(CHDBID)
Contact Metamorphism
Hydrothermal Metamorphism
Dynamothermal Metamorphism
Burial Metamorphism
Impact Metamorphism
Dynamic Metamorphism
A variable temperature, low pressure metamorphism that develops locally where hot magma intrudes relatively cold, upper crustal country rock. (give a product)
Contact Metamorphism (Hornfels, Metaquartzite, Skarn)
Chemical alteration from circulating fluids within cracks and fissures. Pervasive at ocean spreading ridges
that experience tension, thinning and uplift, causes metasomatism. (give a product)
Hydrothermal Metamorphism (Alteration Products, Metallic ore deposits)
Name all major types of Hydrothermal Alteration
(AAACPPPSSSSZ)
Albitic - Albite
Alunitic - Alunite
Argillic - Kaolinite, Smectite, Illite
Carbonatization - Carbonate Minerals (Calcite, etc.)
Phyllic - Sericite, Quartz, Pyrite
Potassic - Biotite, Potassium Feldspar
Propylitic - Chlorite, Epidote, Actinolite, Tremolite
Sericitic - Sericite
Serpentinization - Serpentine
Silication - Quartz, Chert
Spilitization - Albite
Zeolitic - Zeolite Minerals
A regional metamorphism induced by increase in pressure and temperature with non-uniform stress which produces foliated textures, mostly aerially extensive, and dominates convergent margins and associated fold and thrust belts. (give a product)
Dynamothermal Metamorphism (Greenschist, amphibolite, granulite, blueschist, eclogite)
Metamorphism that results from increase in lithostatic stress caused by deep burial of rocks and produces non-foliated textures, affects regional subsiding basins that accumulate thick sequences of sediments and volcanic debris, and usually starts at temperatures 150 °C to 300 °C and gradational with diagenesis at depths of about 8 km. (give a product)
Burial Metamorphism (Non-foliated rocks with low temp. mineral assemblages)
A local form of metamorphism generated by explosive volcanic eruptions or relatively rare collisions of extraterrestrial objects with Earth, causing a high strain rate. (give a product)
Impact Metamorphism (Impactites)
Induced primarily by non-uniform stress in fault zones and shear zones, where the high strain rate is mostly local but extend to a regional scale in large faults or shear zones, and most likely recur in the same fault or shear zone. (Give a product)
Dynamic Metamorphism (Cataclasites, pseudotachylites, mylonites)
A low temperature, brittle grain-fracturing process that involves grain size reduction through the mechanical grinding, rotation and crushing of rock.
Cataclasis
A fine-trained, non-foliated, clastic metamorphic rock produced by cataclastic processes.
Cataclasite
A ductile grain reduction process that produces oriented grains of smaller diameter.
Mylonitization
A product of mylonitization characterized by grain size reduction via macroscopic scale cataclisis, plastic stretching and thinning associated with ductile deformation.
Mylonite
Occurs in metamorphic rocks where individual atoms or molecules can migrate in gaseous, liquid or solid phases from one location in a rock body to a new location.
Diffusion
Involves the dissolution of solid grains under high compressive stress conditions.
Pressolution
An insoluble seam that accumulates as soluble minerals dissolve.
Stylolite
Occurs when existing minerals are transformed under higher temperature and/or pressure conditions, without experiencing a significant change in chemical composition.
Recrystallization
The nucleation and growth of new minerals as pre-existing minerals become unstable due to temperature or pressure changes.
Neocrystallization
Newly formed minerals that are distinctly larger than the minerals in the surrounding matrix.
Porphyroblasts
The segregation of minerals in an initially homogenous rock due to different physical or chemical characteristics such as solubility, ductility, mineral growth or crystallization temperature.
Differentiation
Partially melted rocks that form by quenching under high strain rates in shear zone fractures.
Pseudotachylites
A metamorphic halo in the contact zone that surrounds it, produced from the heat of the igneous intrusion, and
can range from centimeters to hundreds of qmeters in diameter.
Aureole
The size, shape, orientation and intergranular relationships of metamorphic rocks’ constituents that were influenced by temperature and pressure conditions or relict textures.
Metamorphic Textures
Metamorphic textures based on the sizes of the notable grains in metamorphic rocks.
According to Grain Size
Metamorphic textures based on the orientation of the grains in a metamorphic rock.
According to Grain Orientation
Texture defined by large relict grains
Porphyroclasts
Texture defined by large relict grains from the protolith that have experienced deformation but retained its composition.
Porphyroclastic
Oval-shaped feldspar porphyroclasts that are particularly common in gneiss.
Augen
Oval shaped quartz porphyroclasts that are particularly common in gneiss.
Flaser
Texture defined by large grains
Porphyroblasts
Texture defined by large grains that experienced neocrystallization and growth in response to favorable temperature and pressure conditions due to metamorphism.
Porphyroblastic
A texture of metamorphic rocks that exhibit planar
arrangement of mineral grains or structural features of a rock.
Foliated
A texture of metamorphic rocks that exhibit linear arrangement of mineral grains or structural features of a rock.
Lineation
A texture of metamorphic rocks that lack the planar arrangement of mineral grains or structural features of a rock.
Non-Foliated
