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Book Chapter

Laramide crustal shortening

By
Warren B. Hamilton
Warren B. Hamilton
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Published:
January 01, 1988

North America rapidly overrode buoyant oceanic lithosphere during late Late Cretaceous and early Paleogene time. The southwestern United States was retarded by drag against the overridden slab and advanced slightly more slowly than did the continental interior. This resulted in crustal shortening, in a broad zone between the continental subplates, that produced the variably overthrust Laramide basement uplifts of the Rocky Mountain region. The thrust faults flatten downward into the middle crust and are reflective in seismic profiles, likely because diverse crystalline rocks have been transposed along them by ductile shear and flattening.

The increase northward and northwestward, from New Mexico to Wyoming, of crustal shortening across the Laramide belt, and the fanning pattern of northwest-broadening arcs defined by the compressive structures throughout the Rocky Mountain region, indicate that the Colorado Plateau region rotated clockwise, as though about an Euler pole in or near central New Mexico, by perhaps 4° relative to the continental interior. This rotation, combined with the subsequent clockwise relative rotation of the plateau by about 3° about an Euler pole in central Colorado as the Rio Grande rift opened in middle Tertiary time, can be seen in paleomagnetic data.

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GSA Memoirs

Interaction of the Rocky Mountain Foreland and the Cordilleran Thrust Belt

Christopher J. Schmidt
Christopher J. Schmidt
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William J. Perry, Jr.
William J. Perry, Jr.
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Geological Society of America
Volume
171
ISBN print:
9780813711713
Publication date:
January 01, 1988

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