METAMORPHIC PETROLOGY (METAMORPHIC PROCESSES) Flashcards
A low temp, brittle grain fracturing process which involves grain size reduction through mechanical grinding, rotation and crushing of rocks which occurs in high strain rate fault zones whithin the upper crust or in meteorite impacts
Cataclasis
This is a rock characteized by angular grains with finegraine matrix formed by brittle fragmentation due to shearing
Cataclasite
A texture chracterized by angular grains infill between larger grains produced by cataclasis
Mortar texture
Ductile grain reduction process which produces orientated grains of small diameter (foliation) in response to non uniform stress. Deformation occurs vis combination of grain-fracturing, plastic bending and internal deformation with rotation.
Mylonitization
Where does mylonitization occur?
High T High strain shear zones of lower crust and upper mantle
A foliate and sometimes lineated rocks formed by intense ductile deformation and contains porphyroclasts or lithic fragments with the same composition as that of the matrix
Mylonite
This pertains to the migration of individual atoms or molecules in solid, liquid or gaseous phase from one location in a rock body to a new location
Diffusion
In which phase is diffusion most efficient?
Gas
In which liquid viscosity state will diffusion be enhanced?
Low viscosity
Why is diffisuton limited in solids?
Because chemical bonding restricts migration
HOw does diffusion happen in solid state particularly in met rocks?
Diffusion is facilitate by crystal dislocations and by presence of minute amounts of intergranular fluids that serve as catalysts
catalysts of diffusion in high T met processes?
H2O and Co2
What is pressure solution?
A metamorphic process in which high compressive stress conditons results to partial dissolution of solid grains which causes one grain to impinge upon another creating a sutured contact between grains
Which protolith types demonstrate pressure solution?
Calcareous, Quarztofeldsphatic, Pelitic
What is stylolites?
These are seams created by alignment or accumulation of insoluble minerals druing presure solutions
What are the usual minerals forming stylolites?
Mica, Graphite and hematite
This occurs when existing minerals are transformed under high temp and/or pressure without altering their chemical composition which is driven by cyrtal lattice reorganization without breakage
Recrystallization
Differentiate Extracyrstalline and intracystalline recyrtsllatization
Extracrystalline - involves grain rotation or grain boundary migration caused by the addition or removal of mineral material by diffusion
Intracrystalline - occurs within the interal invidual grains due to microscopic movements caused by defects, vacancies or disliocation within a crystal
this is a mean by which crystal defects are minimized by the movement of ions within a grain
Recovery
This refers to the nucleation and growth of new minerals as pre-existing minerals become unstable due to T-P changes and enhanced by diffusion
Neocrystallization
What are porphyroblasts?
These are Newly Formed Minerals or Neocrystallized minerals disticnly larger than the surroinding matrix
This refers to the segregaton of the minerals in an initially homogenous rock due to different physical and chemical characteristiscs such as solubility, ductility, mineral growth or crystallization temperature
Differentiation
In folding, which minerals will tend to concetrate in the hinges? in the limbs?
Hinges -soluble minerals calcite, quartz and felds.
Limbs - ferromags and clays (less solyble)
these grow along rigid grains of porphyroblasts about which more ductile minerals such as micas accumulate
Pressure Shadows
