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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 - PowerPoint PPT Presentation
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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
• Radiolarian Cherts
• Characteristic of ophiolite settings
• Other Distinctive Rocks– Graywacke and Flysch– Blueschist
Bedded Chert
Serpentinite
Serpentinite
Magnesite Mines in Serpentinite
Pillow Lava
Pillow Lava
Pillow Lava
Blueschist
Graywacke
Flysch
Melange
Melange
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
Coesite in Gneiss
Palisade Texture in Quartz
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
• 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• 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
Eclogite