7. Textures 2

Question 1

How can we work out the age of minerals relative to the deformation producing the foliation?

Answer 1

• Matrix textures tend to preserve the last event
• Porphyroblasts often preserve evidence of earlier events
• Porphyroblast-matrix texture → earlier & later events

Question 2

What do equilibrium textures indicate? And where are they formed?

Answer 2

crystal growth and textural re-equilibration after deformation ceased.

Formed in:

• contact metamorphism
• high-grade regional metamorphism where high temperature continued after deformation ceased

Question 3

What is mimetic recrystallisation?

Answer 3

growth controlled by pre-existing grain arrangement

e.g. there is crenulation but no internal deformation of mica

Question 4

Matrix textures tend only to preserve the last deformation event, since recrystallisation at high temperatures usually destroys evidence of prograde events. What can preserve earlier events?

Answer 4

Porphyroblasts

Question 5

What are the three types of porphyroblasts?

Answer 5

pre-kinematic

syn-kinematic

post-kinematic