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Thrust tectonics and Cretaceous intracontinental shortening in Southeast Alaska

Rubin, C. M. and Saleeby, J. B. (1992) Thrust tectonics and Cretaceous intracontinental shortening in Southeast Alaska. In: Thrust Tectonics. Chapman & Hall , London, pp. 407-417. ISBN 9780412438905.

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An imbricate thrust belt extending along strike for more than 2000 km overprints the tectonic boundary between two of the largest allochthonous crustal fragments (Intermontane and Insular superterranes) in the North American Cordillera, and affects rocks west of the Coast Plutonic Complex in southeast Alaska and western British Columbia. Deformation was broadly coeval with mid-Cretaceous magmatism and involved the emplacement of west-directed thrust nappes over a structurally intact and relatively unmetamorphosed basement. The Palaeozoic and lower Mesozoic Alexander terrane forms structural basement for much of the thrust belt along a moderately northeast-dipping decollement. There were two main episodes of mid-Cretaceous deformation, which were contemporaneous with the emplacement of tabular plutonic bodies. Older structures record ductile southwest-vergent folding and faulting, and regional metamorphism, associated with a well-developed axial-planar foliation. Second-generation structures include southwest-directed thrust faults that juxtapose contrasting metamorphic grades and refold earlier structures. Structural, stratigraphical and geochronologic data suggest that regional-scale deformation in southeast Alaska occurred between 113 Ma and 89 Ma. Deformation involved the imbrication of marginal basin(s) and a magmatic arc, overprinting the older tectonic boundary between the Insular superterrane and the late Mesozoic western margin of North America (i.e. the Intermontane supertcrrane). Contractional deformation along the length of the thrust belt was broadly coeval with arc magmatism, and thus records intra-arc tectonism. Late Palaeocene to Early Eocene deformation and uplift may mark the transition from contractional to extensional tectonism, and perhaps records the collapse of tectonically thickened crust.

Item Type:Book Section
Additional Information:© 1992 Chapman & Hall. C.M.R. is grateful for long discussions with Bill McClelland, Meghan Miller, Jim Monger, and Margi Rusmore on Cordilleran tectonics. Field and laboratory work for southeast Alaska regional studies has been supported by US National Science Foundation Grants EAR 86-05386 and EAR 88-03834 (to JBS); additional support (to CMR) was provided by Geological Society of America Penrose Grants, a Sigma-Xi grant-in-aid, and by the US Geological Survey, Alaska Branch. Some of the work reported here was part of a doctoral thesis by C.M.R. at Caltech. The stereonet program was graciously provided by Rick Allmendinger. Informal reviews by Meghan Miller were quite helpful. Hugh Gabrielse, Ken McClay, and Bob Thompson provided very helpful and critical reviews.
Funding AgencyGrant Number
NSFEAR 86-05386
NSFEAR 88-03834
Geological Society of America Penrose Bequest Research GrantsUNSPECIFIED
Sigma-Xi Grants in Aid of ResearchUNSPECIFIED
Record Number:CaltechAUTHORS:20150122-150812988
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54004
Deposited By: Tony Diaz
Deposited On:23 Jan 2015 02:22
Last Modified:03 Oct 2019 07:54

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