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Beauchamp, W.

Superposed folding resulting from inversion of a synrift accommodation zone, Atlas Mountains, Morocco

in K. R. McClay, ed., Thrust Tectonics and Hydrocarbon Systems: AAPG Memoir 82, p. 635-646, 2004.


The conspicuous offset of the northern margin of the High Atlas Mountains is composed of several large superposed folds, one of which is known as the Ait Attab Syncline. The original northeast-trending syncline (F1) was folded by a second set of fold axes (F2) that trend to the northwest. The superposed folding was generated by one phase of compression, with thrusting of synrift rocks northwestward
over a prior accommodation zone formed during rifting. This accommodation zone is expressed in the exposure of synrift rocks, the exposure of Paleozoic strata in the footwall, and a coincident offset of topography. Inversion was accomplished by the transport of synrift strata along reactivated normal faults and newly formed thrusts. The unique pattern of refolding is believed to be characteristic of inversion.

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Key Figures and Captions

Figure 8. The inversion of a synrift accommodation zone (a) by margin-normal shortening created first folds (F1) that are oriented parallel to preexisting ramps and down-to-the-basin normal faults (b). Continued compression across the accommodation zone results in the interference of the first F1 folds and the formation of F2 folding (c). S1 = principal stress component; maximum principal stress.

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