Studied by 4 peopleWhat is the fundamental principle of metamorphic rocks?
The mineral assemblages reflect the physical P-T conditions all the time when the rock formed
How to get a rock in equilibrium
long enough exposure to the same specific P-T conditions, and the rock will assemble into the most stable conditions possible
What is the most stable mineral composition?
The state with the lowest gibbs free energy
What is a petrogenetic grid used for?
Bulk composition of a constant
What is the value of a P-T grid
The actual range of physical conditions under which specific assemblages are stable relative to others
Compositional phase diagrams
Constructed for a specific value of P + T
only phases connected by Tie lines can exist
The system will usually crystallize as a 3 phase system according to the triangular field
What happens if a mineral is not directly connected by tie line?
It cannot stably co-exist
What happens when two minerals react together?
The tie line that connects them is removed
what happens when 2 minerals grow together for the first time?
a new tie line connects them together
What is serpentinite?
Hydrated ultramafic rock, common in mountain belts.
They represent the metamorphosed ocean floor or upper mantle rocks that have been thrust upwards during the orogenic process
Antigorite= Forsterite + talc+ h2O reaction
As we get closer to the pluton, the T of metamorphism is increasing. Antigorite has dehydrated and reached its high-T stability limit to form Fo+ TC+h2O
crossing tie line reaction
A crossing tie line reaction occurs when a rock crosses from one tie line to another as the conditions change during metamorphism.
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