Abstract

The Older pre-Cambrian rocks of central Arizona are divided, in chronological order, into the Yavapai group (previously termed the Yavapai and Pinal schists); Deadman quartzite, Maverick shale, and Mazatzal quartzite; small intrusive bodies; and batholithic masses of granite. A great unconformity separates these rocks from the Younger pre-Cambrian Apache strata.

The Yavapai group is subdivided into the Yaeger greenstone, Red Rock rhyolite, and Alder sedimentary series. These formations are definitely schistose only near intrusive bodies.

In the Older pre-Cambrian rocks the principal regional structures are folds and normal and reverse faults of subparallel, northeast to north trend and shear and normal faults that strike north to west. The folds show northwest to west overturn and northeast to north plunge. The dip of the reverse faults varies from a few degrees to more than 80 degrees southeast.

It is concluded that the principal structures in the Older pre-Cambrian rocks resulted from one profound crustal disturbance—the Mazatzal Revolution—which took place after the Mazatzal quartzite, and long before the Apache strata, were laid down. Marked by intense northwestward compression and culminating with the batholithic invasion of the only pre-Cambrian granite recognized in the region, this revolution doubtless gave rise to a huge range, the roots of which are unconformably overlapped by Paleozoic strata.

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