Metamorphic petrology - L1 Flashcards
What is metamorphism?
subsolidus process leading to changes in
mineralogy and/or texture and often in chemical composition in a rock
What is the metamorphism for pyroxene?
Pyroxene to chlorite
What information might be retained with rocks which have undergone metamorphism?
enough inherited information from protolith to potentially determine pre-metamorphic history
What is the word for the action of metamorphism?
Metamorphose
What can you call rock that has been altered by metamorphism?
the rock has been metamorphosed
At what temperature will metamorphism begin?
after diagenesis around 100-150*c
What is temperature like around the end of metamorphic range?
at 900*c metamorphism ends and shifts to anataxis
What is protolith?
original rock
What to factors control the metamorphism?
an increase in pressure and temperature (temp most important)
What is the variation of temperature over depth called?
geothermal gradient
What are the effects of increasing temp with metamorphism?
Recrystallisation promoted
Increase grain size
Driver of chemical reactions
What is the reason for the promotion of recrystallisation due to temp increase with metamorphism?
due to large surface area to volume ratio
What happens to grain size during metamorphism due to increased temp?
fine aggregates coalesce to form larger grains
What does coalesce mean?
come together to form one mass
What variable will lead to increased pressure?
depth
How can the physical conditions at depth be described?
temperature-pressure (T/P) coupling
How can geological setting affect T/P coupling?
High T/ Low P at or near magmatic intrusion (hot)
What is lithostatic pressure stress like?
uniform stress (hydrostatic)
Does lithostatic pressure affect the texture of metamorphic rocks?
No no effect
What is the pressure like with Deviatoric pressure?
varies in different directions
What will deviatoric pressure due to metamorphic rock pressure?
induce characteristic pressure
What will deviatoric pressure do to rocks?
induce grain rotation and realignment (perpendicular to mass compression)
What texture will deviatoric pressure produce?
fabric (cleavage, schistocity)
What can lead to the production of localised metamophism?
shear stress at transform margins
What are mylonites?
typical metamorphic rocks found deep at shear zones
How do fluids relate to metamorphism?
facilitate metamorphic processes
What are the typical fluids related to metamorphic processes?
H2O (most common), CO2, CH4, N2, S
What are fluids needed to produce in metamorphic areas?
hydrous carbonate phases
What are some examples of fluids required to form some metamorphic rocks?
meteoric ,juvenile magmatic
subducted material, trapped sedimentary brines, or degassing of the
mantle
What is the speed of metamorphism like?
solid-state process so very slow
How long do large temperature changes needed for metamorphism take?
tens of millions of years
How can the long time for large temp change affect metamophism?
frequently cause it to be incomplete so many relics can be found in rock record
What cab be used to classify metamorphic rocks?
metamorphic grade
How does the metamorphic grade classify metamorphic rocks?
indicates intensity if metamorphism (P/T) without saying exact pressure temp relationship
