METAMORPHIC PETROLOGY (METAMORPHIC PROCESSES)

Question 1

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

Answer 1

Cataclasis

Question 2

This is a rock characteized by angular grains with finegraine matrix formed by brittle fragmentation due to shearing

Answer 2

Cataclasite

Question 3

A texture chracterized by angular grains infill between larger grains produced by cataclasis

Answer 3

Mortar texture

Question 4

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.

Answer 4

Mylonitization

Question 5

Where does mylonitization occur?

Answer 5

High T High strain shear zones of lower crust and upper mantle

Question 6

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

Answer 6

Mylonite

Question 7

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

Answer 7

Diffusion

Question 8

In which phase is diffusion most efficient?

Answer 8

Gas

Question 9

In which liquid viscosity state will diffusion be enhanced?

Answer 9

Low viscosity

Question 10

Why is diffisuton limited in solids?

Answer 10

Because chemical bonding restricts migration

Question 11

HOw does diffusion happen in solid state particularly in met rocks?

Answer 11

Diffusion is facilitate by crystal dislocations and by presence of minute amounts of intergranular fluids that serve as catalysts

Question 12

catalysts of diffusion in high T met processes?

Answer 12

H2O and Co2

Question 13

What is pressure solution?

Answer 13

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

Question 14

Which protolith types demonstrate pressure solution?

Answer 14

Calcareous, Quarztofeldsphatic, Pelitic

Question 15

What is stylolites?

Answer 15

These are seams created by alignment or accumulation of insoluble minerals druing presure solutions

Question 16

What are the usual minerals forming stylolites?

Answer 16

Mica, Graphite and hematite

Question 17

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

Answer 17

Recrystallization

Question 18

Differentiate Extracyrstalline and intracystalline recyrtsllatization

Answer 18

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

Question 19

this is a mean by which crystal defects are minimized by the movement of ions within a grain

Answer 19

Recovery

Question 20

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

Answer 20

Neocrystallization

Question 21

What are porphyroblasts?

Answer 21

These are Newly Formed Minerals or Neocrystallized minerals disticnly larger than the surroinding matrix

Question 22

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

Answer 22

Differentiation

Question 23

In folding, which minerals will tend to concetrate in the hinges? in the limbs?

Answer 23

Hinges -soluble minerals calcite, quartz and felds.
Limbs - ferromags and clays (less solyble)

Question 24

these grow along rigid grains of porphyroblasts about which more ductile minerals such as micas accumulate

Answer 24

Pressure Shadows