Ductile extrusion in continental collision zones: Ambiguities in the definition of channel flow and its identification in ancient orogens
Field characteristics of crustal extrusion zones include: high-grade metamorphism flanked by lower-grade rocks; broadly coeval flanking shear zones with opposing senses of shear; early ductile fabrics successively overprinted by semi-brittle and brittle structures; and localization of strain to give...
| Published in: | Geological Society, London, Special Publications |
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| Main Authors: | , , , |
| Other Authors: | , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
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Geological Society Publishing House
2006
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| Subjects: | |
| Online Access: | http://hdl.handle.net/2440/49952 https://doi.org/10.1144/GSL.SP.2006.268.01.09 |
| Summary: | Field characteristics of crustal extrusion zones include: high-grade metamorphism flanked by lower-grade rocks; broadly coeval flanking shear zones with opposing senses of shear; early ductile fabrics successively overprinted by semi-brittle and brittle structures; and localization of strain to give a more extensive deformation history within the extrusion zone relative to the flanking regions. Crustal extrusion, involving a combination of pure and simple shear, is a regular consequence of bulk orogenic thickening and contraction during continental collision. Extrusion can occur in response to different tectonic settings, and need not necessarily imply a driving force linked to mid-crustal channel flow. In most situations, field criteria alone are unlikely to be sufficient to determine the driving causes of extrusion. This is illustrated with examples from the Nanga Parbat-Haramosh Massif in the Pakistan Himalaya, and the Wing Pond Shear Zone in Newfoundland. R. R. Jones, R. E. Holdsworth, M. Hand and B. Goscombe |
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