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Detailed Reference Information |
Paterson, S.R., Miller, R.B., Alsleben, H., Whitney, D.L., Valley, P.M. and Hurlow, H. (2004). Driving mechanisms for >40 km of exhumation during contraction and extension in a continental arc, Cascades core, Washington. Tectonics 23. doi: 10.1029/2002TC001440. issn: 0278-7407. |
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In the NW North American Cordillera, the Cascades core region of the Coast Plutonic Complex underwent Late Cretaceous (>96 Ma to locally 73 Ma) SW-NE contraction and crustal thickening followed by dextral transpression (~73 to 55 Ma), then transtension (3 mm/yr) by local thrusting in regions undergoing crustal thickening. In the central part of the core (Chelan block), >40 km of exhumation occurred between 91 and 45 Ma, about half of which occurred during early contraction (driven by thrusting) and half during top-to-north, arc-oblique shear during reactivation of a midcrustal Cretaceous thrust, the Dinkelman decollement. The footwall of this thrust consists of the Swakane Biotite Gneiss, a Cretaceous, metaclastic assemblage with recorded pressures of 10--12 kbar, no arc-related magmatism, and structures dominated by pervasive top-to-north shearing. The hanging wall consists of the Napeequa Complex, an oceanic assemblage with recorded pressures of 6--12 kbar, voluminous arc-related magmatism, and complex structures indicating early top-to-WSW shearing, younger top-to-north shearing, and widespread folding. In the Napeequa, top-to-north shearing started by 73 Ma during melt-present conditions at pressures ≥6 kbar. Top-to-north shearing in both hanging wall and footwall continued during exhumation (~1.6 mm/yr) and cooling to greenschist facies conditions during which slip became increasingly localized, eventually resulting in formation of pseudotachylite on discrete slip surfaces. We suggest that arc-oblique extension was driven by along-arc heterogeneity in displacements/erosion, initially during transpression and underplating of continental sediments, and later during transtension. |
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Abstract |
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Keywords
Tectonophysics, Continental tectonics—general, Structural Geology, Local crustal structure, Cascades core, continental arc, exhumation, tectonics, Napeequa, Swakane |
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Publisher
American Geophysical Union 2000 Florida Avenue N.W. Washington, D.C. 20009-1277 USA 1-202-462-6900 1-202-328-0566 service@agu.org |
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