The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 80 to 70 million years ago, and ended 55 to 35 million years ago. The exact duration and ages of beginning and end of the orogeny are in dispute. The Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The major feature that was created by this orogeny was deep-seated, thick-skinned deformation, with evidence of this orogeny found from Canada to northern Mexico, with the easternmost extent of the mountain-building represented by the Black Hills of South Dakota. The phenomenon is named for the Laramie Mountains of eastern Wyoming. The Laramide orogeny is sometimes confused with the Sevier orogeny, which partially overlapped in time and space.[1]
The Laramide orogeny was caused by subduction of a plate at a shallow angle.
The orogeny is commonly attributed to events off the west coast of North America, where the Kula and Farallon Plates were sliding under the North American plate. Most hypotheses propose that oceanic crust was undergoing flat-slab subduction, that is, subduction at a shallow angle. As a consequence, no magmatism occurred in the central west of the continent, and the underlying oceanic lithosphere actually caused drag on the root of the overlying continental lithosphere. One cause for shallow subduction may have been an increased rate of plate convergence. Another proposed cause was subduction of thickened oceanic crust.
Magmatism associated with subduction occurred not near the plate edges (as in the volcanic arc of the Andes, for example), but far to the east, along the Colorado Mineral Belt.[2] Geologists call such a lack of volcanic activity near a subduction zone a magmatic gap. This particular gap may have occurred because the subducted slab was in contact with relatively cool continental lithosphere, not hotter asthenosphere.[3] One result of shallow angle of subduction and the drag that it caused was a broad belt of mountains, some of which were the progenitors of the Rocky Mountains. Part of the proto-Rocky Mountains would be later modified by extension to become the Basin and Range Province.
The Laramide orogeny produced intermontane structural basins and adjacent mountain blocks by means of deformation. This style of deformation is typical of continental plates adjacent to convergent margins of long duration that have not sustained continent/continent collisions. This tectonic setting produces a pattern of compressive uplifts and basins, with most of the deformation confined to block edges. Twelve kilometers of structural relief between basins and adjacent uplifts is not uncommon. The basins contain several thousand meters of Paleozoic and Mesozoicsedimentary rocks that predate the Laramide orogeny. As much as 5,000 meters (16,000 ft) of Cretaceous and Cenozoic sediments filled these orogenically-defined basins. Deformed Paleocene and Eocene deposits record continuing orogenic activity.[4]
During the Laramide orogeny, basin floors and mountain summits were much closer to sea level than today. After the seas retreated from the Rocky Mountain region, floodplains, swamps, and vast lakes developed in the basins. Drainage systems imposed at that time persist today. Since the Oligocene, episodic epeirogenic uplift gradually raised the entire region, including the Great Plains, to present elevations. Most of the modern topography is the result of Pliocene and Pleistocene events, including additional uplift, glaciation of the high country, and denudation and dissection of older Cenozoic surfaces in the basin by fluvial processes.[4]
Topographic map of the western United States (and part of Canada) showing the Bighorn Basin (highlighted in orange), formed by the Laramide Orogeny
In the United States, these distinctive intermontane basins occur principally in the central Rocky Mountains from Colorado and Utah (Uinta Basin) to Montana and are best developed in Wyoming, with the Bighorn, Powder River, and Wind River being the largest. Topographically, the basin floors resemble the surface of the western Great Plains, except for vistas of surrounding mountains.[4]
At most boundaries, Paleozoic through Paleogene units dip steeply into the basins off uplifted blocks cored by Precambrian rocks. The eroded steeply dipping units form hogbacks and flatirons. Many of the boundaries are thrust or reverse faults. Although other boundaries appear to be monoclinal flexures, faulting is suspected at depth. Most bounding faults show evidence of at least two episodes of Laramide (Late Cretaceous and Eocene) movement, suggesting both thrust and strike-slip types of displacement.[4]
Ecological consequencesedit
According to paleontologist Thomas M. Lehman, the Laramide orogeny triggered "the most dramatic event that affected Late Cretaceous dinosaur communities in North America prior to their extinction."[5] This turnover event saw the replacement of specialized and highly ornamented centrosaurine and lambeosaurines by more basal upland dinosaurs in the south, while northern biomes became dominated by Triceratops with a greatly reduced hadrosaur community.[6]
Dumitru, T.A.; Gans, P.B.; Foster, D.A.; Miller, E.L. (1991). "Refrigeration of the western Cordilleran lithosphere during Laramide shallow-angle subduction". Geology. 19 (11): 1145–1148. Bibcode:1991Geo....19.1145D. doi:10.1130/0091-7613(1991)019<1145:ROTWCL>2.3.CO;2.
English, Joseph M.; Johnston, Stephen T. (2004). "The Laramide Orogeny: What Were the Driving Forces?". International Geology Review. 46 (9): 833–838. Bibcode:2004IGRv...46..833E. doi:10.2747/0020-6814.46.9.833. S2CID 129901811.
Lehman, T. M. (2001). "Late Cretaceous dinosaur provinciality". In Tanke, D. H.; Carpenter, K. (eds.). Mesozoic Vertebrate Life. Indiana University Press. pp. 310–328.
Liu, L.; Gurnis, M.; Seton, M.; Saleeby, J.; Müller, R.D.; Jackson, J.M. (2010). "The role of oceanic plateau subduction in the Laramide orogeny" (PDF). Nature Geoscience. 3 (5): 353–357. Bibcode:2010NatGe...3..353L. doi:10.1038/ngeo829.
Livaccari, Richard F.; Burke, Kevin; Sengor, AMC (1981). "Was the Laramide orogeny related to subduction of an oceanic plateau?". Nature. 289 (5795): 276–278. Bibcode:1981Natur.289..276L. doi:10.1038/289276a0. S2CID 27153755.
Saleeby, Jason (2003). "Segmentation of the Laramide Slab -- Evidence from the southern Sierra Nevada region" (PDF). Geological Society of America Bulletin. 115: 655–668. Bibcode:2003GSAB..115..655S. doi:10.1130/0016-7606(2003)115<0655:sotlsf>2.0.co;2.
Schellart, W.P.; Stegman, D.R.; Farrington, R.J.; Freeman, J.; Moresi, L. (16 July 2010). "Cenozoic Tectonics of Western North America Controlled by Evolving Width of Farallon Slab". Science. 329 (5989): 316–319. Bibcode:2010Sci...329..316S. doi:10.1126/science.1190366. PMID 20647465. S2CID 12044269.
Willis, Grant C. (2000). "I thought that was the Laramide orogeny!". Utah's Sevier Thrust System. Utah Geological Survey.
External linksedit
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February 16, 2024
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The Laramide orogeny was a time period of mountain building in western North America which started in the Late Cretaceous 80 to 70 million years ago and ended 55 to 35 million years ago The exact duration and ages of beginning and end of the orogeny are in dispute The Laramide orogeny occurred in a series of pulses with quiescent phases intervening The major feature that was created by this orogeny was deep seated thick skinned deformation with evidence of this orogeny found from Canada to northern Mexico with the easternmost extent of the mountain building represented by the Black Hills of South Dakota The phenomenon is named for the Laramie Mountains of eastern Wyoming The Laramide orogeny is sometimes confused with the Sevier orogeny which partially overlapped in time and space 1 The Laramide orogeny was caused by subduction of a plate at a shallow angle The orogeny is commonly attributed to events off the west coast of North America where the Kula and Farallon Plates were sliding under the North American plate Most hypotheses propose that oceanic crust was undergoing flat slab subduction that is subduction at a shallow angle As a consequence no magmatism occurred in the central west of the continent and the underlying oceanic lithosphere actually caused drag on the root of the overlying continental lithosphere One cause for shallow subduction may have been an increased rate of plate convergence Another proposed cause was subduction of thickened oceanic crust Magmatism associated with subduction occurred not near the plate edges as in the volcanic arc of the Andes for example but far to the east along the Colorado Mineral Belt 2 Geologists call such a lack of volcanic activity near a subduction zone a magmatic gap This particular gap may have occurred because the subducted slab was in contact with relatively cool continental lithosphere not hotter asthenosphere 3 One result of shallow angle of subduction and the drag that it caused was a broad belt of mountains some of which were the progenitors of the Rocky Mountains Part of the proto Rocky Mountains would be later modified by extension to become the Basin and Range Province Contents 1 Basins and mountains 2 Ecological consequences 3 See also 4 Footnotes 5 References 6 External linksBasins and mountains editThe Laramide orogeny produced intermontane structural basins and adjacent mountain blocks by means of deformation This style of deformation is typical of continental plates adjacent to convergent margins of long duration that have not sustained continent continent collisions This tectonic setting produces a pattern of compressive uplifts and basins with most of the deformation confined to block edges Twelve kilometers of structural relief between basins and adjacent uplifts is not uncommon The basins contain several thousand meters of Paleozoic and Mesozoic sedimentary rocks that predate the Laramide orogeny As much as 5 000 meters 16 000 ft of Cretaceous and Cenozoic sediments filled these orogenically defined basins Deformed Paleocene and Eocene deposits record continuing orogenic activity 4 During the Laramide orogeny basin floors and mountain summits were much closer to sea level than today After the seas retreated from the Rocky Mountain region floodplains swamps and vast lakes developed in the basins Drainage systems imposed at that time persist today Since the Oligocene episodic epeirogenic uplift gradually raised the entire region including the Great Plains to present elevations Most of the modern topography is the result of Pliocene and Pleistocene events including additional uplift glaciation of the high country and denudation and dissection of older Cenozoic surfaces in the basin by fluvial processes 4 nbsp Topographic map of the western United States and part of Canada showing the Bighorn Basin highlighted in orange formed by the Laramide OrogenyIn the United States these distinctive intermontane basins occur principally in the central Rocky Mountains from Colorado and Utah Uinta Basin to Montana and are best developed in Wyoming with the Bighorn Powder River and Wind River being the largest Topographically the basin floors resemble the surface of the western Great Plains except for vistas of surrounding mountains 4 At most boundaries Paleozoic through Paleogene units dip steeply into the basins off uplifted blocks cored by Precambrian rocks The eroded steeply dipping units form hogbacks and flatirons Many of the boundaries are thrust or reverse faults Although other boundaries appear to be monoclinal flexures faulting is suspected at depth Most bounding faults show evidence of at least two episodes of Laramide Late Cretaceous and Eocene movement suggesting both thrust and strike slip types of displacement 4 Ecological consequences editAccording to paleontologist Thomas M Lehman the Laramide orogeny triggered the most dramatic event that affected Late Cretaceous dinosaur communities in North America prior to their extinction 5 This turnover event saw the replacement of specialized and highly ornamented centrosaurine and lambeosaurines by more basal upland dinosaurs in the south while northern biomes became dominated by Triceratops with a greatly reduced hadrosaur community 6 See also edit nbsp Earth sciences portal nbsp Paleontology portalLaramide Belt Sevier orogeny earlier than the Laramide orogeny in the Cretaceous era Nevadan orogeny still earlier in the late Jurassic early Cretaceous era Geology of the Rocky Mountains Geology of the Pacific NorthwestFootnotes edit Willis 2000 Jones Craig Farmer Lang Sageman Brad Zhong Shijie 2012 Hydrodynamic mechanism for the Laramide orogeny Geosphere 7 1 183 doi 10 1130 GES00575 1 Dumitru et al 1991 a b c d nbsp This article incorporates public domain material from Hegde M Wyoming Intermontane Basins National Aeronautics and Space Administration Archived from the original on 2011 06 17 Lehman 2001 p 310 Lehman 2001 p 324References editDumitru T A Gans P B Foster D A Miller E L 1991 Refrigeration of the western Cordilleran lithosphere during Laramide shallow angle subduction Geology 19 11 1145 1148 Bibcode 1991Geo 19 1145D doi 10 1130 0091 7613 1991 019 lt 1145 ROTWCL gt 2 3 CO 2 English Joseph M Johnston Stephen T 2004 The Laramide Orogeny What Were the Driving Forces International Geology Review 46 9 833 838 Bibcode 2004IGRv 46 833E doi 10 2747 0020 6814 46 9 833 S2CID 129901811 Lehman T M 2001 Late Cretaceous dinosaur provinciality In Tanke D H Carpenter K eds Mesozoic Vertebrate Life Indiana University Press pp 310 328 Liu L Gurnis M Seton M Saleeby J Muller R D Jackson J M 2010 The role of oceanic plateau subduction in the Laramide orogeny PDF Nature Geoscience 3 5 353 357 Bibcode 2010NatGe 3 353L doi 10 1038 ngeo829 Livaccari Richard F Burke Kevin Sengor AMC 1981 Was the Laramide orogeny related to subduction of an oceanic plateau Nature 289 5795 276 278 Bibcode 1981Natur 289 276L doi 10 1038 289276a0 S2CID 27153755 Saleeby Jason 2003 Segmentation of the Laramide Slab Evidence from the southern Sierra Nevada region PDF Geological Society of America Bulletin 115 655 668 Bibcode 2003GSAB 115 655S doi 10 1130 0016 7606 2003 115 lt 0655 sotlsf gt 2 0 co 2 Schellart W P Stegman D R Farrington R J Freeman J Moresi L 16 July 2010 Cenozoic Tectonics of Western North America Controlled by Evolving Width of Farallon Slab Science 329 5989 316 319 Bibcode 2010Sci 329 316S doi 10 1126 science 1190366 PMID 20647465 S2CID 12044269 Willis Grant C 2000 I thought that was the Laramide orogeny Utah s Sevier Thrust System Utah Geological Survey External links edit nbsp Wikimedia Commons has media related to Laramide Orogeny Maps animation detailed information UCLA U Wisconsin article Retrieved from https en wikipedia org w index php title Laramide orogeny amp oldid 1179161889, wikipedia, wiki, book, books, library,
