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Subduction Zone and High Pressure Rocks

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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Subduction Zone and High Pressure Rocks

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  1. Subduction Zone and High Pressure Rocks

  2. Granulite Facies • High T, P • Base of Crust • T > 700 C • Very anhydrous • Dry conditions inhibit melting

  3. About 600 C

  4. About 680 C

  5. About 700 C

  6. About 750 C

  7. Subduction Zone Rocks

  8. Steinmann Trinity (1905) • Serpentinite • Pillow Basalt • Radiolarian Cherts • Characteristic of ophiolite settings • Other Distinctive Rocks • Graywacke and Flysch • Blueschist

  9. Bedded Chert

  10. Serpentinite

  11. Serpentinite

  12. Magnesite Mines in Serpentinite

  13. Pillow Lava

  14. Pillow Lava

  15. Pillow Lava

  16. Blueschist

  17. Graywacke

  18. Flysch

  19. Melange

  20. Melange

  21. 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

  22. Coesite in Gneiss

  23. Palisade Texture in Quartz

  24. 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

  25. 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

  26. 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

  27. Eclogite

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