Pelites. Chapter 14 and 18. Mudstones and shales Accumulate in wedge of sed. Off continental shelf Boring muds: interesting metamorphosed Clays sensitive to P&T changes. High Al 2 O 3 and K 2 O Low CaO. Barrow’s Area. Seen in regional met.
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Chapter 14 and 18
Over what P-T range is the
assemblage Gar+Chl+Bio stable?
Step 1: find AFM range for assemblage
Where in P-T space does this assemblage occur?
Al2SiO5 in nearby rx could further restrict P&T
Step 2: use AFM labels to find P-T field
This is the only part of P-T space where gar+chl+bio can coexist
3. Correlation with mafic rocks
What is the equivalent metamorphic facies?
What assemblage would be present in interlayered mafic rocks?
epid/czo + hbl+ plag
Interpreting complex assemblages
What are the possible interpretations??
…look for textural evidence of rxn
…chl replacing Grt, St, or Bt; don’t plot chl
…no textural evidence of rxn
…observations lead to interpretations
a) Reaction frozen in, V=1
b) Extra component, e.g. Mn, Ca in Grt or Zn in St
c) Retrograde mineral, e.g. chlorite