Subduction Zone and High Pressure Rocks

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Subduction Zone and High Pressure Rocks
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Granulite Facies

• High T, P
• Base of Crust
• T gt 700 C
• Very anhydrous
• Dry conditions inhibit melting

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About 600 C
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About 680 C
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About 700 C
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About 750 C
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Subduction Zone Rocks
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Steinmann Trinity (1905)

• Serpentinite
• Pillow Basalt
• Radiolarian Cherts
• Characteristic of ophiolite settings
• Other Distinctive Rocks
• Graywacke and Flysch
• Blueschist

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Bedded Chert
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Serpentinite
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Serpentinite
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Magnesite Mines in Serpentinite
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Pillow Lava
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Pillow Lava
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Pillow Lava
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Blueschist
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Graywacke
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Flysch
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Melange
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Melange
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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

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Coesite in Gneiss
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Palisade Texture in Quartz
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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

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Eclogite

• Start with Basalt Labradorite (An Ab)
  Diopside Olivine
• Ab breaks down to Jadeite Quartz
• Jadeite Diopside Omphacite
• Anorthite Olivine Garnet
• Final compositionOmphacite Garnet Quartz
• Plagioclase no longer stable

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Types of Eclogite

• Type A kimberlites, dunites, volcanic pipes (Py
  70, Alm 20 Tgt900 C)
• Metamorphism of mantle rocks
• Type B high-pressure gneiss terranes (Py 45,
  Alm 40 T500-900 C)
• Crustal thickening and deep metamorphism
• Type C blueschists (Py 10, Alm 60 Tlt500 C)
• Next stage after blueschist metamorphism

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Eclogite