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Title: Cordilleran slab windows

Abstract

The geometry and geologic implications of subducted spreading ridges are topics that have bedeviled earth scientists ever since the recognition of plate tectonics. As a consequence of subduction of the Kula-Farallon and East Pacific rises, slab windows formed and migrated beneath the North American Cordillera. The probable shape and extent of these windows, which represent the asthenosphere-filled gaps between two separating, subducting oceanic plates, are depicted from the Late Cretaceous to the present. Possible effects of the existence and migration of slab windows on the Cordillera at various times include cessation of arc volcanism and replacement by rift or plate-edge volcanism; lithospheric uplift, attenuation, and extension; and increased intensity of compressional tectonism. Eocene extensional tectonism and alkaline magmatism in southern British Columbia and the northwestern United States were facilitated by slab-window development.

Authors:
;  [1]
  1. (Carleton Univ., Ottawa, Ontario (Canada))
Publication Date:
OSTI Identifier:
6967026
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geology; (USA); Journal Volume: 17:9
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; NORTH AMERICA; PLATE TECTONICS; GEOLOGIC MODELS; BRITISH COLUMBIA; CONSTRAINTS; CRETACEOUS PERIOD; GEOLOGIC HISTORY; GROUND UPLIFT; MAGMA; OCEANIC CRUST; OREGON; SUBDUCTION ZONES; VOLCANISM; WASHINGTON; CANADA; EARTH CRUST; FEDERAL REGION X; GEOLOGIC AGES; MESOZOIC ERA; TECTONICS; USA; 580000* - Geosciences

Citation Formats

Thorkelson, D.J., and Taylor, R.P. Cordilleran slab windows. United States: N. p., 1989. Web. doi:10.1130/0091-7613(1989)017<0833:CSW>2.3.CO;2.
Thorkelson, D.J., & Taylor, R.P. Cordilleran slab windows. United States. doi:10.1130/0091-7613(1989)017<0833:CSW>2.3.CO;2.
Thorkelson, D.J., and Taylor, R.P. 1989. "Cordilleran slab windows". United States. doi:10.1130/0091-7613(1989)017<0833:CSW>2.3.CO;2.
@article{osti_6967026,
title = {Cordilleran slab windows},
author = {Thorkelson, D.J. and Taylor, R.P.},
abstractNote = {The geometry and geologic implications of subducted spreading ridges are topics that have bedeviled earth scientists ever since the recognition of plate tectonics. As a consequence of subduction of the Kula-Farallon and East Pacific rises, slab windows formed and migrated beneath the North American Cordillera. The probable shape and extent of these windows, which represent the asthenosphere-filled gaps between two separating, subducting oceanic plates, are depicted from the Late Cretaceous to the present. Possible effects of the existence and migration of slab windows on the Cordillera at various times include cessation of arc volcanism and replacement by rift or plate-edge volcanism; lithospheric uplift, attenuation, and extension; and increased intensity of compressional tectonism. Eocene extensional tectonism and alkaline magmatism in southern British Columbia and the northwestern United States were facilitated by slab-window development.},
doi = {10.1130/0091-7613(1989)017<0833:CSW>2.3.CO;2},
journal = {Geology; (USA)},
number = ,
volume = 17:9,
place = {United States},
year = 1989,
month = 9
}
  • COCORP and petroleum industry seismic reflection profiles in northwestern Montana reveal the structure of the Cordilleran foreland thrust belt. The Front Ranges consist of thick thrust sheets containing Precambrian Belt Supergroup and Paleozoic miogeoclinal shelf rocks above a thin remnant of Paleozoic rocks and gently westward-dipping North American basement. Interpretation of the seismic data and results from a recent petroleum exploration well suggest that 15-22 km of Precambrian Belt Supergroup sedimentary rocks are present in several thrust plates beneath the eastern Purcell anticlinorium. Previous hypotheses of a large mass of Paleozoic miogeoclinal sedimentary rocks or slices of crystalline basement locatedmore » beneath the eastern Purcell anticlinorium do not appear to be supported by the data. The easternmost occurrence of allochthonous basement is interpreted to be in the western part of the anticlinorium near the Montana-Idaho border. Comparison of the Cordilleran foreland thrust belt in northwestern Montana and southern Canada suggest that a change in the deep structure of the Purcell anticlinorium occurs along strike. The anticlinorium in southern Canada has been interpreted as a hanging-wall anticline that was thrust over the western edge of thick Proterozoic North American basement, whereas in northwestern Montana the anticlinorium appears to consist of a complex series of thrust sheets above highly attenuated North American basement.« less
  • The region is characterized by bundles of en echelon folds cut by two major fault systems, the Richardson fault array bordering the foreland and the Kaltag fault zone transecting the foldbelt. Late Cretaceous and Tertiary horizontal contraction with concomitant vertical thickening of the supracrustal wedge is roughly one-fourth that of the eastern Cordillera of southern Canada. Potential hydrocarbon traps in Paleozoic and Mesozoic rocks of the northern Cordillera commonly occur within these en echelon fold bundles. In the Cenozoic succession of the Arctic coastal plain and continental shelf, however, closures are arranged only crudely en echelon. Current estimates of themore » combined oil and gas resources of the eastern Cordilleran foldbelt of northern Canada and the adjacent interior platform are about 10 billion bbl of oil and 123 tcf of natural gas.« less
  • A cogenetic and coeval tonalitic and mafic dike swarm has been identified within a southern fragment (the Owens Mountain area) of the western Foothills terrane (California). The dikes were mylonitized and transposed (rotated into subparallel orientation) during emplacement, from 155 to 148 Ma (U-Pb zircon data), which coincides in time with the Nevadan orogeny. Steeply southeast-plunging fold axes and S-fold geometries indicate a sinistral-sense of shear, possibly with some dip-slip motion as well. This shear zone may be the southern and possibly deeper extension of the Bear Mountains fault zone. This and other Late Jurassic Cordilleran dike swarms record amore » complex pattern of sinistral-sense transtension-transpression that developed at the apparent-polar-wander J2 cusp ([approximately] 150 Ma) and during subsequent, rapid, northwestward acceleration of North America. The Late Jurassic Nevadan orogeny is a manifestation of these dramatic changes in magnitude and direction of North American motion.« less
  • To address outstanding questions in Mesozoic-Cenozoic structure and present-day deep physicochemical state in the region of the southern Cordilleran hingeline, a detailed, east-west profile of magnetotelluric (MT) soundings 155 km in length was acquired. From these soundings, a resistivity interpretation was produced using an inversion algorithm based on a structural parameterization. In the upper ten kilometers of the transect, the interpretation shows two segments of low resistivity lying beneath allochthonous rocks of the Late Mesozoic, Sevier thrust sheet. Subsequent industry drilling motivated in part by this surveying confirms the existence and position of the eastern subthrust conductor and, more spectacularly,more » identifies the presence of yet deeper, autochthonous Mesozoic rocks. A simple structural interpretation is offered where one underthrust segment of low-resistivity sediments was created originally, but this segment was broken later into two major ones during higher-angle Tertiary extension. For the middle and lower crust, the MT data imply a nearly 1-D resistivity structure of remarkable uniformity across the entire transect. Pre-existing structural fabrics have had no measurable influence on localizing regions of high temperature fluids and melting in the lower crust, at least averaged over the scale of tens of kilometers. Given its uniformity over a distance of 155 km or more, the depth to the regional deep conductor does not appear related to the distribution of high-temperature geothermal resources.« less
  • No abstract prepared.