Three-Dimensional Structural Geometries of the Colorado River Extensional Terrane and Their Regional Exploration Implications
Published:January 01, 1996
Eric G. Frost, Thomas L. Heidrick, 1996. "Three-Dimensional Structural Geometries of the Colorado River Extensional Terrane and Their Regional Exploration Implications", Tertiary Extension and Mineral Deposits, Southwestern U.S., William A. Rehrig, James J. Hardy
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This field trip is designed to give its participants and readers of the guidebook a regional crustal perspective of the geometries and exploration insight into mineral deposits within highly extended terranes. This trip focuses on a traverse from Las Vegas, Nevada, to Parker, Arizona, as a guide to demonstrate many of the primary structural features involved in these extensional terranes and their interrelationships to each other. By beginning in the highest crustal levels exposed near Las Vegas and descending structurally down into the crust toward the deep crustal exposures in the Whipple Mountains, this field trip route effectively descends along the structural features from their highest crustal exposures to their deepest exposures. The enormity of the terrane and its linked character in both structure and geochemistry is highlighted by this approach. The features within the Colorado River extensional terrane are profoundly interesting in and of themselves, but the primary benefit of this trip and field guide will be to people studying similar crustal extensional geometries in other areas. Because fluid flow is so strongly controlled by the structural geometries, exploration for minerals and oil and gas can be very significantly aided by considering the structural geometries described in this trip.
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Tertiary Extension and Mineral Deposits, Southwestern U.S.
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