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Laramide monoclines occur in the Phanerozoic rocks in the Grand Canyon region above a block-faulted, northeastward-tilted Precambrian foundation composed of crystalline metamorphic rocks; the crystalline rocks are mantled by northeastward-thickening wedges of Middle and Late Proterozoic Grand Canyon Supergroup sedimentary and volcanic rocks. The structural character of the Precambrian complex is one of heterogeneous lithologies and is highly anisotropic, owing primarily to imprinted Middle and Late Proterozoic north-, northeast-, and northwest-trending reverse and normal faults, and secondarily to foliation within the metamorphics and layered fabrics within the Grand Canyon Supergroup.

Most Grand Canyon monoclines are underlain by a single, west-dipping, high-angle, Precambrian normal fault that was reactivated during Laramide west-southwest–east-northeast compression. Laramide reverse slip was opposite in sense to the Precambrian motion. The structural anisotropies provided by these faults are the single most influential element that localized deformation of the Laramide monoclines.

The Laramide monoclines are wholly contained within the Phanerozoic section in areas directly underlain by Precambrian crystalline rocks. However, the anticlinal axial surfaces of the monoclines extend downward into the hanging walls which contain ductile Precambrian sedimentary rocks. The extent of such folding is proportional to the thickness of the Precambrian sedimentary rocks. Folding of the ductile Precambrian strata in the hanging wall caused the profiles of the monoclines to broaden laterally into the hanging walls.

Structural anisotropies associated with strong foliation in the Precambrian crystalline rocks and layering in the Precambrian Grand Canyon Supergroup did not influence appreciably Laramide deformation in the Grand Canyon region.

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