3. Graphical Representation 1

Question 1

Mineral assemblage vs paragenesis

Answer 1

Assemblage: The set of minerals present in a metamorphic rock, not necessarily all formed at the same time (can include secondary alteration minerals)

Paragenesis: a set of minerals in equilibrium together as any one time (at a given P & T)

Question 2

What is a metamorphic zone?

Answer 2

metamorphic zones represent changes in metamorphic grade in an aureole reflected by progressive change in the peak-metamorphic mineral parageneses in the marbles

Each metamorphic zone is characterised by the appearence of a new index mineral: a mineral if restricted P-T stability, used to map out differences in metamorphic grade

Question 3

What are incompatible parageneses?

Answer 3

When rocks of identical bulk comp. have different peak parageneses because they have been subjected to different T (and/or P) conditions at the peak of metamorphism

(their tie-lines cross and tie-triangles overlap)

Question 4

What are compatible parageneses?

Answer 4

Different parageneses that can exist at the same P and T in rocks with different bulk compositions

(non-crossing tie-lines and non-overlapping tie-triangles)