Download - 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 > 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 composition:Omphacite + Garnet + Quartz
• Plagioclase no longer stable
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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
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Eclogite