No description available.

No description available.

A sequence of Older Precambrian volcanic and sedimentary rocks more than 15,000 feet thick occurs in the Blackjack Mountains and White Ledges, 20 miles north of Globe, Arizona. This sequence consists of (from older to younger) the Redmond formation (acidic volcanic rocks) and the Hess Canyon group (clastic sedimentary rocks). The Hess Canyon group is subdivided into: the White Ledges formation (interbedded quartzites and argillaceous rocks); the Yankee Joe formation (argillaceous strata with interbedded graywackes and arkoses); and the Blackjack formation (argillaceous quartzites). These rocks have been intruded by the Ruin Granite (a porphyritic quartz monzonite) and subsequently eroded to approximately the present level of exposure prior to the deposition of the Younger Precambrian Apache Group. The unconformity between the Older and Younger Precambrian strata is well exposed at Butte Creek north of Haystack Butte. Diabase has intruded the Blackjack formation, the Ruin Granite and the Apache Group. No Paleozoic or Mesozoic rocks are known to occur within the surveyed area. Sediments and volcanic and sedimentary rocks of Tertiary and Quaternary age partly conceal the older rocks. The Hess Canyon group can be correlated with the Deadman Quartzite, Maverick Shale, and Mazatzal Quartzite of the Mazatzal Mountains (Wilson 1939a) and also the Houden Formation of the Diamond Butte Quadrangle (Gastil 1958). Whole rock Rb-Sr dating indicates an age of 1,510 ± m.y. for the Redmond formation. Isotopic dating of the Ruin Granite near the Blackjack Mountains and of the granitic rocks intruded the Mazatzal Quartzite of Four Peaks in the southern Mazatzal Mountains indicates that the Mazatzal Orogeny (the Mazatzal Revolution of Wilson, 1939a) occurred 1,425 to 1,380 m.y. ago in central Arizona. This orogeny followed the deposition of the Mazatzal Quartzite and the Hess Canyon group, terminating older Precambrian time in Arizona and was followed by the deposition of the Younger Precambrian Apache Group. Isotopic dating of volcanic metamorphic and plutonic rocks in the Pinal and Tortilla Mountains and near Roosevelt Dam on the Salt River indicate that portions of the Pinal Schist in the type locality are greater than 1,730 m.y. old and that these rocks have experienced a complex series of events in Older Precambrian times. The Madera Diorite of Ransome (1903) consists of rocks 1,730 ± 30 m.y. old as well as rocks about 1,500 m.y. old. The Older Precambrian igneous rocks in this part of Arizona appear to have developed from material similar in Rb to Sr ratio to average shallow continental crust. These rocks formed during the interval 1,730 to 1,370 m.y. ago. The continental crust in this region probably originated no earlier than about 1,800 m.y. ago. Igneous rocks younger than 1,370 m.y. have not been derived soley from average shallow crustal material.

No description available.

No description available.

No description available.

Foy Ridge is located about twenty-six miles south-southwest of Tucson, Arizona, and about a mile north of the Twin Buttes mining district. The sediments of the Roy Ridge area range in age from Cambrian to Recent. Separation of the Paleozoic section into mappable units has been complicated by post-Permian metamorphism. This metamorphism has destroyed any fossils that were probably once present, although a few remains of a Devonian Cladopora reef have been recognized. The metamorphism has caused a recrystallization of the limestones and an alteration of the shales to hornfels with stringers of epidote. The result is a sequence of altered Paleozoic rocks closely resembling one another. Lateral compression acting in a northeast-southwest direction played the major role in the tectonic history of the Foy Ridge area. Foy Ridge is the inverted limb of a large fold overturned to the northeast. As the fold was being produced thrust faults and wrench faults formed in the limbs. These first faults were cut off by the Foy Ridge fault that formed in the southwest limb of a northwest plunging anticline. This anticline was thrust forward (southwest) and upward until it was pressed against the inverted limb (Foy Ridge) and the adjacent fold. A disharmonic fold probably formed in the normal limb of the major fold of which Foy Ridge is a part. Thrust faults in the disharmonic fold repeated the lower Paleozoic section on the southwest side of Foy Ridge. As compression continued the last major thrust of the area was produced. This was the Bolsa Overthrust, which probably originated in the core of the disharmonic fold. It cut across the inverted limb of the major fold and may have also cut across the crest of the northwest plunging anticline northeast of the Foy Ridge fault. Intrusive activity followed or accompanied the overthrusting and folding of the area. This was closely followed by post-intrusion normal faulting. The Twin Buttes, two prominent hills immediately east of the thesis area, are a southeastern extension of the northeastern limb of the northwest plunging anticline that formed the hanging wall of the Foy Ridge fault. The "breached anticline" of the Twin Buttes mining district is probably related to the normal limb of the fold that formed Foy Ridge. The synclinal area between these two folds is covered by alluvium.

No description available.

No description available.

No description available.