Geologic Setting of Mineral Deposits of the Granite Wash Mountains, La Paz County, West -Central Arizona
Stephen J. Reynolds, Jon E. Spencer, Stephen E. Laubach, Sondra S. Peacock, Stephen M. Richard, W. Dickson Cunningham, 1996. "Geologic Setting of Mineral Deposits of the Granite Wash Mountains, La Paz County, West -Central Arizona", Tertiary Extension and Mineral Deposits, Southwestern U.S., William A. Rehrig, James J. Hardy
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The Granite Wash Mountains are located in west-central Arizona and are contiguous with the Harcuvar Mountains to the northeast and the Little Harquahala Mountains to the south. They are part of the Maria fold and thrust belt, a belt of large folds and major thrust faults that trends east-west through west-central Arizona and southeastern California (Reynolds and others, 1986; Spencer and Reynolds, 1990). In the Granite Wash Mountains, late Mesozoic deformation related to the Maria belt affected a diverse suite of rock units, including Proterozoic crystalline rocks, Paleozoic carbonate and quartzose clastic rocks, and Mesozoic sedimentary, volcanic, plutonic, and hypabyssal rocks. This deformation was mostly deep seated and produced an assortment of folds, cleavages, and both ductile and brittle shear zones. Several discrete episodes of deformation occurred, resulting in refolded folds, folded and refolded thrust faults, and complex repetition, attenuation, and truncation of stratigraphic sequences. Greenschist-facies metamorphism accompanied deformation and was most intense along the major thrusts. Deformation and metamorphism were followed by emplacement of two Late Cretaceous intrusions and numerous Cretaceous to mid-Tertiary dikes.
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Starting in Las Vegas, we will traverse through many of the geometric elements and complexities of hanging wall deformation above the regional detachment systems of the Colorado River extensional terrane. We will study the interaction of normal faults as arranged in regional, crustal-scale mega-domains and the bounding structures that separate these tilt domains. As we progress through the classic Eldorado Mountains-Hoover Dam region, where many of the ideas of listric normal faulting were first popularized, we will see both the real rocks and the historic rationale for their deformation. By examining the listric versus domino models for normal faulting, we will utilize different geometric techniques for determining the depth to the detachment structures and percent extension. Continuing further south toward southernmost Nevada, we will cross the accommodation zone that separates the Lake Mead and Whipple dip domains and further descend to deeper structural levels to examine lower levels of the major normal faults and their tilting of upper-crustal blocks and associated offset along the regional detachment faults. Fluid flow within the shattered fault zones and its relationship to the 3-D geometries of the fault surfaces will be studied both along the faults and within the hydrothermally altered and mineralized wallrocks.
(From Las Vegas proper, drive east on Tropicana to Pecos, south to Russell, then continue east to Southern Nevada Vocational Technical Center. Follow signs to its entrance then drive around edge of campus to dirt road on northern edge, which provides elevated view toward the north to Frenchman Mountain. View is much better in the afternoon than in the morning.)
Stop 1-1: Frenchman Mountain Tilt Block
(Return to Russell Road, turn right to freeway (1.4 miles) and south along freeway to Boulder City. Take truck route, Buchanan Blvd., around Boulder City and turn off highway at “Lakeview Overlook,” about 5 miles pastBoulder City for view and discussion of Lake Mead shear zone.)
Stop 1-2: Lake Mead Shear Zone and Associated Alteration by Hydrothermal Fluids
(Return to Highway 93 and continue descent to Hoover Dam. Park in new parking structure and walk to gorge overlook about 100 meters up the road on the Nevada side for best view of structural features.)
Stop 1-3: Extension Within the Volcanic Rocks Exposed at Hoover Dam
(Return to Boulder City along Highway 93 and to turnoff to Highway 95 south toward Searchlight. Note extreme alteration at junction of Highways 93 and 95. Continue south