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Basin and Range Province

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The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins. The physiography of the province is the result of tectonic extension that began around 17 million years ago in the early Miocene epoch.

One of various geographical definitions of the Province

The numerous ranges within the province in the United States are collectively referred to as the "Great Basin Ranges", although many are not actually in the Great Basin. Major ranges include the Snake Range, the Panamint Range, the White Mountains, and the Sandia Mountains. The highest point fully within the province is White Mountain Peak in California, while the lowest point is the Badwater Basin in Death Valley at −282 feet (−86 m).[1] The province's climate is arid, with numerous ecoregions. Most North American deserts are located within it.

The Basin and Range Province should not be confused with the Great Basin, a region defined by its unique hydrological characteristics (internal drainage) that overlaps much of the greater Basin and Range physiographic region. Nor should it be confused with the Basin and Range National Monument, located in Southern Nevada, which is one small part of the much larger province.

Geography

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NASA satellite photo of typical Basin and Range topography across central Nevada

The Basin and Range Province includes much of western North America. In the United States, it is bordered on the west by the eastern fault scarp of the Sierra Nevada and spans over 500 miles (800 km) to its eastern border marked by the Wasatch Fault, the Colorado Plateau and the Rio Grande Rift. The province extends north to the Columbia Plateau and south as far as the Trans-Mexican Volcanic Belt in Mexico, though the southern boundaries of the Basin and Range are debated.[2] In Mexico, the Basin and Range Province is dominated by and largely synonymous with the Mexican Plateau.

Evidence suggests that the less-recognized southern portion of the province is bounded on the east by the Laramide Thrust Front of the Sierra Madre Oriental and on the west by the Gulf of California and Baja Peninsula with notably less faulting apparent in the Sierra Madre Occidental in the center of the southernmost Basin and Range Province.[3]

Common geographic features include numerous endorheic basins, ephemeral lakes, plateaus, and bolson valleys alternating with mountains (as described below). The area is mostly arid and sparsely populated, although there are several major metropolitan areas, such as Reno, Las Vegas, Salt Lake City, Phoenix, Tucson, El Paso—Ciudad Juárez, Mexicali, and Hermosillo.

Geology

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It is generally accepted that basin and range topography is the result of extension and thinning of the lithosphere, which is composed of crust and upper mantle. Extensional environments like the Basin and Range are characterized by listric normal faulting, or faults that level out with depth. Opposing normal faults link at depth producing a horst and graben geometry, where horst refers to the upthrown fault block and graben to the down dropped fault block.

The average crustal thickness of the Basin and Range Province is approximately 30–35 km and is comparable to extended continental crust around the world.[4] The crust in conjunction with the upper mantle comprises the lithosphere. The base of the lithosphere beneath the Basin and Range is estimated to be about 60–70 km.[5] Opinions vary regarding the total extension of the region; however, the median estimate is about 100% total lateral extension.[6] Total lateral displacement in the Basin and Range varies from 60 to 300 km since the onset of extension in the Early Miocene with the southern portion of the province representing a greater degree of displacement than the north. Evidence exists to suggest that extension initially began in the southern Basin and Range and propagated north over time.[7]

Clarence Dutton famously compared the many narrow parallel mountain ranges that distinguish the unique topography of the Basin and Range to an "army of caterpillars crawling northward."[8]

Tectonics

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Snake Range

The tectonic mechanisms responsible for lithospheric extension in the Basin and Range province are controversial, and several competing hypotheses attempt to explain them. Key events preceding Basin and Range extension in the western United States include a long period of compression due to the subduction of the Farallon Plate under the west coast of the North American continental plate which stimulated the thickening of the crust. Most of the pertinent tectonic plate movement associated with the province occurred in the Neogene period (23.03-2.58 million years ago) and continues to the present. By the Early Miocene sub-epoch (23.03-15.97 million years ago), much of the Farallon Plate had been consumed, and the seafloor spreading ridge that separated the Farallon Plate from the Pacific Plate (Pacific-Farallon Ridge) approached North America.[9] In the Middle Miocene (15.97-11.63 million years ago), the Pacific-Farallon Ridge was subducted beneath North America ending subduction along this part of the Pacific margin; however, the Farallon Plate continued to subduct into the mantle.[9] The movement at this boundary divided the Pacific-Farallon Ridge and spawned the San Andreas transform fault, generating an oblique strike-slip component.[10] Today, the Pacific Plate moves north-westward relative to North America, a configuration which has given rise to increased shearing along the continental margin.[9]

The tectonic activity responsible for the extension in the Basin and Range is a complex and controversial issue among the geoscience community. The most accepted hypothesis suggests that crustal shearing associated with the San Andreas Fault caused spontaneous extensional faulting similar to that seen in the Great Basin.[11] However, plate movement alone does not account for the high elevation of the Basin and Range region.[11] The western United States is a region of high heat flow which lowers the density of the lithosphere and stimulates isostatic uplift as a consequence.[12] Lithospheric regions characterized by elevated heat flow are weak and extensional deformation can occur over a broad region. Basin and Range extension is therefore thought to be unrelated to the kind of extension produced by mantle upwelling which may cause narrow rift zones, such as those of the Afar Triple Junction.[13] Geologic processes that elevate heat flow are varied, however some researchers suggest that heat generated at a subduction zone is transferred to the overriding plate as subduction proceeds. Fluids along fault zones then transfer heat vertically through the crust.[14] This model has led to increasing interest in geothermal systems in the Basin and Range, and requires consideration of the continued influence of the fully subducted Farallon plate in the extension responsible for the Basin and Range Province.

Metamorphic core complexes

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In some localities in the Basin and Range, metamorphic basement is visible at the surface. Some of these are metamorphic core complexes (MCC), an idea that was first developed based on studies in this province. A metamorphic core complex occurs when lower crust is brought to the surface as a result of extension. MCCs in the Basin and Range were not interpreted as being related to crustal extension until after the 1960s. Since then, similar deformational patterns have been identified in MCCs in the Basin and Range and has led geologists to examine them as a group of related geologic features formed by crustal extension during the Cenozoic era (66.0 million years ago to present). The study of metamorphic core complexes has provided valuable insight into the extensional processes driving Basin and Range formation.[15]

Volcanism

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Main article: List of large volume volcanic eruptions in the Basin and Range Province
See also: Geologic timeline of Western North America and Yellowstone hotspot

Prior to the Eocene Epoch (55.8 ±0.2 to 33.9 ±0.1 Ma) the convergence rate of the Farallon and North American Plates was fast, the angle of subduction was shallow, and the slab width was huge. During the Eocene the Farallon Plate subduction-associated compressive forces of the Laramide, Sevier and Nevada orogenies ended, plate interactions changed from orthogonal compression to oblique strike-slip, and volcanism in the Basin and Range Province flared up (Mid-Tertiary ignimbrite flare-up). It is suggested that this plate continued to be underthrust until about 19 Ma, at which time it was completely consumed and volcanic activity ceased, in part. Olivine basalt from the oceanic ridge erupted around 17 Ma and extension began.[16][17][18][19]

Volcanic areas

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Mineral resources

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In addition to small amounts of Nevada petroleum, the Basin and Range Province supplies nearly all the copper and most of the gold, silver, and barite mined in the United States.[citation needed]

See also: Copper mining in Arizona, Gold mining in Nevada, Silver mining in Arizona, and Silver mining in Nevada

See also

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References

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  1. ^ "USGS National Elevation Dataset (NED) 1 meter Downloadable Data Collection from The National Map 3D Elevation Program (3DEP) – National Geospatial Data Asset (NGDA) National Elevation Data Set (NED)". United States Geological Survey. September 21, 2015. Archived from the original on March 25, 2019. Retrieved September 22, 2015.
  2. ^ Henry, C; Aranda-Gomez, J (1992). "The real southern Basin and Range: Mid- to late Cenozoic extension in Mexico". Geology. 20 (8): 20701–04. Bibcode:1992Geo....20..701H. doi:10.1130/0091-7613(1992)020<0701:TRSBAR>2.3.CO;2.
  3. ^ Dickinson, William R. (2002). "The Basin and Range Province as a Composite Extensional Domain". International Geology Review. 22 (1): 1–38. Bibcode:2002IGRv...44....1D. doi:10.2747/0020-6814.44.1.1. S2CID 73617479.
  4. ^ Mooney, Walter D; Braile, Lawrence W (1989). "The seismic structure of the continental crust and upper mantle of North America". The Geology of North America – An Overview. Geological Society of America. p. 42.
  5. ^ Zandt, G; Myers, S; Wallace, T (1995). "Crust and mantle structure across the Basin and Range-Colorado Plateau boundary at 37°N latitude and implications for Cenozoic extensional mechanism". J. Geophys. Res. 100 (B6): 10529–10548. Bibcode:1995JGR...10010529Z. doi:10.1029/94JB03063.
  6. ^ "Geologic Provinces of the United States: Basin and Range Province". USGS. Archived from the original on 2009-01-25.
  7. ^ Salyards, Stephen L; Shoemaker, Eugene M (1987). "Landslide and debris-flow deposits in the Thumb Member of the Miocene Horse Spring Formation on the east side of Frenchman Mountain, Nevada: A measure of basin-range extension". In Hill, Mason L (ed.). Centennial Field Guide. Vol. 1. Cordilleran Section of the Geological Society of America. doi:10.1130/0-8137-5401-1.49.
  8. ^ Dutton, Clarence (1885). "Mount Taylor and the Zuni Plateau". Sixth Annual Report of the United States Geological Survey to the Secretary of the Interior, 1884-1885. U.S. Geological Survey: 113–198. doi:10.3133/ar6.
  9. ^ a b c Riney, Brad (2000). "Plate Tectonics". Ocean Oasis Field Guide. San Diego Natural History Museum. Archived from the original on 2011-01-02. Retrieved 5 Dec 2010.
  10. ^ "Basin and Range Province – Tertiary Extension". Digital Geology of Idaho. Archived from the original on 11 September 2019. Retrieved 5 Dec 2010.
  11. ^ a b Stanley, SM (2005). Earth system history. New York: Freeman.
  12. ^ Cengage, Gale (2003). Lerner, Lee; Lerner, Brenda Wilmoth (eds.). "Basin and Range Topography". World of Earth Science. eNotes.com. Archived from the original on 2010-10-31. Retrieved 5 Dec 2010.
  13. ^ Stern, Robert J (2010-09-01), "Rifts", Physics and Chemistry of the Solid Earth (Class Notes), Dallas, Texas: University of Texas at Dallas
  14. ^ Yamano, Makoto; Kinoshita, Masataka; Goto, Shusaku (2008). "High heat flow anomalies on an old oceanic plate observed seaward of the Japan Trench". International Journal of Earth Sciences. 97 (2): 345–352. Bibcode:2008IJEaS..97..345Y. doi:10.1007/s00531-007-0280-1. S2CID 129417881.
  15. ^ Rystrom, VL (2000). "Metamorphic Core Complexes". Archived from the original on 2010-11-03. Retrieved 5 Dec 2010.
  16. ^ McKee, E. H. (1971). "Tertiary Igneous Chronology of the Great Basin of Western United States – Implications for Tectonic Models". Geological Society of America Bulletin. 82 (12): 3497–3502. Bibcode:1971GSAB...82.3497M. doi:10.1130/0016-7606(1971)82[3497:ticotg]2.0.co;2.
  17. ^ "Northwest Origins, An Introduction to the Geologic History of Washington State, Catherine L. Townsend and John T. Figge". The Burke Museum of Natural History and Culture, University of Washington. Retrieved 2010-04-10.
  18. ^ "Oregon: A Geologic History". Oregon Department of Geology and Mineral Industries. Archived from the original on 2010-01-28. Retrieved 2010-03-26.
  19. ^ "Digital Geology of Idaho, Laura DeGrey and Paul Link". Idaho State University. Archived from the original on 2018-07-21. Retrieved 2010-04-10.
  20. ^ Wood, Charles A.; Jűrgen Kienle (1993). Volcanoes of North America. Cambridge University Press. pp. 284–86. ISBN 978-0521438117.

Further reading

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