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Subduction Zone and High Pressure Rocks. Granulite Facies. High T, P Base of Crust T > 700 C Very anhydrous Dry conditions inhibit melting. About 600 C. About 680 C. About 700 C. About 750 C. Subduction Zone Rocks. Steinmann Trinity (1905). Serpentinite Pillow Basalt

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granulite facies
Granulite Facies
  • High T, P
  • Base of Crust
  • T > 700 C
  • Very anhydrous
  • Dry conditions inhibit melting
steinmann trinity 1905
Steinmann Trinity (1905)
  • Serpentinite
  • Pillow Basalt
  • Radiolarian Cherts
  • Characteristic of ophiolite settings
  • Other Distinctive Rocks
    • Graywacke and Flysch
    • Blueschist
coesite in quartz
Coesite in Quartz
  • Not very dramatic
  • Rare
  • Relict in inclusions, often in garnet
  • Mostly reverts to quartz
  • Distinctive “palisade” texture in quartz
  • Radial fractures due to 10% volume increase
garnets
Garnets
  • Pyralspite series (Mg-Fe-Mn)
    • Pyrope Mg3Al2Si3O12
    • Almandine Fe3Al2Si3O12
    • Spessartite Mn3Al2Si3O12
  • Ugrandite Series (Ca + Fe-Al-Cr)
    • Gossularite Ca3Al2Si3O12
    • Andradite Ca3(Fe, Ti)2Si3O12
    • Uvarovite Ca3Cr2Si3O12
eclogite
Eclogite
  • Start with Basalt: Labradorite (An + Ab) + Diopside + Olivine
  • Ab breaks down to Jadeite + Quartz
  • Jadeite + Diopside = Omphacite
  • Anorthite + Olivine = Garnet
  • Final composition:Omphacite + Garnet + Quartz
  • Plagioclase no longer stable
types of eclogite
Types of Eclogite
  • Type A: kimberlites, dunites, volcanic pipes (Py 70%, Alm 20% T>900 C)
    • Metamorphism of mantle rocks
  • Type B: high-pressure gneiss terranes (Py 45%, Alm 40% T=500-900 C)
    • Crustal thickening and deep metamorphism
  • Type C: blueschists (Py 10%, Alm 60% T<500 C)
    • Next stage after blueschist metamorphism