Deep Subduction of Continental Crust
The continental crust on the downgoing plate is deeply subducted as part of the downgoing plate during collision, defined as buoyant crust entering a subduction zone. An unknown proportion of subducted continental crust returns to the surface as ultra-high pressure (UHP) metamorphic terranes, which contain metamorphic coesite and/or diamond plus or minus unusual silicon-rich garnets and/or potassium-bearing pyroxenes. The presence of these minerals demonstrate subduction of continental crust to at least 90–140 km deep. Examples of UHP terranes are known from the Dabie–Sulu belt of east-central China, the Western Alps, the Himalaya of India, the Kokchetav Massif of Kazakhstan, the Bohemian Massif of Europe, the Western Gneiss Region of Norway, and Mali. Most UHP terranes consist of an imbricated sheets or nappes. The fact that most UHP terranes consist of thin sheets suggests that much thicker, volumetrically dominant tracts of continental crust are more deeply subducted.
Read more about this topic: Continental Collision
Famous quotes containing the words deep and/or crust:
“We cannot set aside an hour for discussion with our children and hope that it will be a time of deep encounter. The special moments of intimacy are more likely to happen while baking a cake together, or playing hide and seek, or just sitting in the waiting room of the orthodontist.”
—Neil Kurshan (20th century)
“Under the day’s crust a half-eaten child ...”
—John Ashbery (b. 1927)