GEOS100 - metamorphic rocks cheat sheet
This is a draft cheat sheet. It is a work in progress and is not finished yet.
Formed under high heat and low pressure and have an interlocking grain appearance like marble
Formed under earth's interior under high pressure and high heat in directed pressure, causing a banded appearance like schist
Types of Metamorphism
Produces an aureole around an intrusive body and occurs when rock is heated by an igneous intrusion. Results in non-foliated textures eg, limestone to marble.
Produces most metamorphic rocks which are usually very foliated, from areas that have undergone change in physical conditions like temp, pressure, and stress. eg, shale to slate
Regional metamorphism of basalt
Metamorphic rocks derived from basalt have more
minerals containing iron and magnesium than slate
and the foliation is less pronounced.
Greenschist - low grade; ferromagnesian mineral are
hydrated to form chlorite.
Amphibolite - higher grade than greenschist; chlorite
& other minerals lose water and convert to amphibole.
Granulite - high grade; amphiboles are further
dehydrated to produce pyroxene and garnets; little
orientation of the minerals
Subduction zone metamorphism
Special conditions of high pressure and low temp; rock exhibits foliation and is called blueschist; higher grade rock is called eclogite
Aureole - an area that surrounds metamorphized rock due to being in contact with an igneous intrusion
Changes that happen when a rock is subjected to temps/pressures higher than where they formed.
Protolith can be any type of rock.
Recrystallization in the solid state
Change in texture and mineralogy of the rock due to the new environment
reflects the intensity/grade of metamorphism and is indicated by the sequential appearance of index minerals and by textures.
Common index minerals in ascending order of P/T: chlorite, muscovite (mica), biotite (mica), garnet, staurolite.
quartz and feldspar are always stable.
Burial metamorphism is the mild alteration of rock that occurs in deep sedimentary basins and ocean trenches
Index minerals - a mineral that forms under specific pressure and temperature to provide metamorphic history.
Controlling Factors in Metamorphism
Heat: most important agent of metamorphism
Influences the mobility and reactivity of chemically active fluids and is the result of intrusive igneous bodies or earths internal heat
Composition of protolith
Chemical composition is inherited from the parent rock
Changes the physical characteristics of rocks
Confining pressure applies forces equally in all directions and causes harder and denser metamorphic rocks
Directed pressure applies unequal pressure in different directions and causes distortion
Chemically active fluids present
At depth, higher temps and pressures cause minerals to dehydrate. Ions are expelled with the water and can travel to cause recrystallization