A geologist's guide to the core complex geology along the Catalina Highway, Tucson Area, Arizona

Spencer, J.E.

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Citation

Spencer, J.E., 2006, A geologist's guide to the core complex geology along the Catalina Highway, Tucson Area, Arizona. Arizona Geological Survey Open File Report, OFR-06-01, 38 p.

Description

The Catalina Highway, which extends from the Tucson metropolitan area up the south side of the Santa Catalina Mountains to the top of the range, provides easy access to some very interesting geology as well as spectacular views and an escape from the summer heat. The south flank of the range, if not the entire range, was uplifted and uncovered from deep beneath the Tucson basin and Tucson Mountains by several tens of kilometers of top-SW displacement on the Catalina detachment fault*, an Oligo-Miocene low-angle normal fault (e.g., Dickinson, 1991). This fault dips gently southward beneath the Tucson Basin and is exposed at only a few small localities on private property at the foot of the range. This shallowly buried fault is better exposed to the southeast where it follows a sinuous course at the foot of the Rincon Mountains (Fig. 1). The northern part of the Tucson basin is largely a half graben in the hanging wall of this fault. All of the rocks visible along the highway make up the footwall block of the Catalina detachment fault. These rocks consist dominantly of Eocene muscovite leucogranite and pegmatite sills within Proterozoic granite, with middle Proterozoic and Paleozoic metasedimentary rocks preserved at the crest of the range (Keith et al., 1980; Force, 1997). The foliated leucogranites and banded gneisses visible along the highway were emplaced and deformed in the middle crust, at depths of perhaps 8 to 15 km, until Oligo-Miocene tectonic exhumation uplifted and uncovered them and tilted the range to the northeast. Shearing in the middle crust, down dip from the detachment fault during its early movement history, produced mylonitic fabrics in these rocks that are the primary focus of this field guide. Asymmetric petrofabrics that allow determination of shear sense in the mylonitic rocks reveal a complex history of deformation. This field guide is directed primarily at observing these mylonitic fabrics and evaluating their shear-sense indicators, and is also a guide to some short hikes to scenic areas with interesting core-complex geology. ( 38 pages)

URI

http://hdl.handle.net/10150/629628

Additional Links

https://library.azgs.arizona.edu/

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Series/Report no.

OFR-06-01

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Collection Information

Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact azgs-info@email.arizona.edu.

North Bounding Coordinate

32.6162

South Bounding Coordinate

32.2384

West Bounding Coordinate

-110.976

East Bounding Coordinate

-110.533

Collections

AZGS Document Repository