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Three-dimensional model of Paleozoic basement beneath Amargosa Desert and Pahrump Valley, California and Nevada: Implications for tectonic evolution and water resources

1998; United States Department of the Interior; Linguagem: Inglês

10.3133/ofr98496

2332-4899

Richard J. Blakely, R.L. Morin, Edwin H. McKee, Kevin M. Schmidt, V. E. Langenheim, G.L. Dixon,

Geological Studies and Exploration

A three-dimensional inversion of gravity data from the Amargosa Desert and Pahrump Valley reveals a topographically complex pre-Cenozoic basement surface concealed by younger sedimentary and volcanic deposits.The Amargosa Desert is underlain by a deep, steep-sided trough extending from the southwest Nevada volcanic complex to the Nevada-California state line.The linear margins of the Amargosa Desert trough and its internal topography suggest that it formed as a series of transtensional basins that transferred strain between right-stepping, northwest-striking, right-lateral, strike-slip faults.Pahrump Valley is underlain by two deep, steep-sided sub-basins separated by a narrow basement ridge aligned parallel to the state line.The Pahrump Valley sub-basins also formed as transtensional pull-apart basins, accommodated in part by displacement along the northwest-striking State Line fault zone.The state-line ridge at Pahrump Valley is on strike with a narrow basement ridge beneath Ash Meadows, also lying along the state line and within the State Line fault zone.Both ridges are associated with late Cenozoic faulting.The ridges may have formed as transpressional structures, caught slightly askew of the northwest-directed strain that formed the sub-basins.Carbonate rocks probably compose the basement beneath most of the Amargosa Desert and Pahrump Valley.Because carbonate rocks are important aquifers in this region, the three-dimensional aspects of the concealed basement surface strongly influence ground-water flow paths and transport rates.For example, the deeper parts of the Amargosa Desert trough, or faults that bound the western margin of the trough, may impede the westward flow of ground water through the carbonate aquifer.If so, the gravity analysis predicts that water discharging at Ash Meadows originates entirely from the carbonate flow path north and northeast of Ash Meadows, whereas water discharging at Furnace Creek originates from the volcanic flow path north and northwest of Furnace Creek.