Crustal Flow and Kinematic Hinges in Metamorphic Core Complexes from the North American Cordillera and the Aegean
Abstract
Detachments are the defining structures of metamorphic core complexes (mcc's), but important clues to how mcc's form and evolve occur in the high-grade structures beneath detachments. Ductile fabrics in mcc rocks record the history of construction and collapse (including fixed- and free-boundary collapse) of orogens. During fixed-boundary collapse, crust flows laterally in response to pressure gradients, and the flowing crust is separated from the rigid crustal lid by a long-lived (channel) detachment. During free-boundary collapse, the lid is extended, and a new detachment develops that steps down to deeper crustal levels at the margin between the hot channel and cooler crust at the front of the channel (e.g., Cordilleran foreland; Lycian Nappes, Turkey). Under this rolling hinge style detachment, normal faulting and doming rapidly exhume orogenic crust. Migmatite- and orthogneiss-cored domes commonly occur beneath detachments in the N. American Cordillera (Thor-Odin, Valhalla, Okanogan-Kettle, Priest River, Bitterroot, Pioneer) and Aegean (Naxos, Ios, Paros, Mykonos, Menderes). Ductile structures in leucogranites that typically pond under detachments record the timing of switch from lateral (channel) flow to extension. Kinematic indicators in leucogranites (Ladybird leucogranite in the N Cordillera; metagranite in the S Menderes Massif, SMM) show a reversal of shear sense (a kinematic hinge) across the mcc's. We have identified kinematic hinges in the Thor-Odin dome region of the Shuswap Complex, BC, and in the SMM, Turkey. The position of the hinge relative to the rolling hinge detachment in the Shuswap (40 km) and to a more diffuse S detachment in the schists of the SMM (15-20 km) corresponds to the amount of extension, which in turn is consistent with the amount of crustal thinning associated with crustal flow (e.g., from 60 to 30 km crustal thickness in the Shuswap). For mcc's without a kinematic hinge (Okanogan, USA; Naxos, Greece), uniform sense of shear may indicate that exhumed crust flowed under channel-style detachments.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.T24C..04W
- Keywords:
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- 8011 Kinematics of crustal and mantle deformation;
- 8109 Continental tectonics: extensional (0905)