Abstract

In southern Arizona, a profound change in tectonic regime from quiescence to major instability took place near the beginning of Mesozoic time. One manifestation of this instability was the free gliding of large blocks of Paleozoic sedimentary rocks into fault troughs containing volcanic material and continental sediments. In the northwestern Canelo Hills, a succession of exotic blocks composed of Permian sedimentary rocks is intercalated with the Canelo Hills Volcanics of Triassic(?)-Jurassic age. The blocks are as large as 400 m thick and 2 km in strike length. Bedding faults, slickensides, and open-space breccias formed near the base of each Permian block during epidermal gliding, whereas the underlying sediments of the Canelo Hills Volcanics deformed by penecontemporaneous flow.

Slickenside and fold-axis orientations place northeast-southwest constraints on the direction of block emplacements. The sense of movement is interpreted to have been northeast to southwest because paleocurrent directions for red beds within the Canelo Hills Volcanics are dominantly southwest and the stratigraphy of the glide blocks is most similar to Permian rocks to the northeast. Palinspastic reconstruction of the blocks to a provenance northeast of the Canelo Hills fits present models of distribution of Permian formations in southern Arizona. Slide block emplacement was synchronous with Triassic(?)-Jurassic vertical movements along northwest-striking fault zones in southern Arizona. One of these fault zones, the Sawmill Canyon, marks the approximate northeast boundary of the Canelo Hills and in early Mesozoic time furnished a scarp from which the slide blocks were derived.

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