Good Example Of How AND Why Did The Southern Rockies Rise? Research Paper
Commonly recognized as the ‘Southern Rockies’, the Southern Rocky Mountains are situated in Northern America, forming a key part of the Rocky Mountains. The question of how these enormous chunks came into existence from their parent range can only been answered by geology.
The geological study of this range tells us that that the Southern Rockies are the result of excessive tectonic activity. Plate boundaries are borders that occur due to the interaction of two plates. A study tells us that the Southern Rockies were separated from their plate boundary after which they rose due to the tectonic activity. The mountain peaks of the present-day
Southern Rocky Mountains are the highest peaks in the Rocky Mountain system (Gordon P. Eaton 1). It is said that the collision of the North American tectonic plate and the Pacific plate were instrumental in the formation of the Southern Rockies. Although geologists have come up with various theories, the elevation of the Southern Rockies has always been a million dollar question for most. This is because of its unusual physical features and magmatic activity.
It is said that the base of these mountains represent a second generation of mountains after the accumulation of the chalk and shale sediments. Topographically, individual peaks of the Colorado- New Mexico region are said to be the highest peaks. This is the followed by the middle range with an average height of 3690m in the south eastern part of the Northern Rocky mountains. During this period, the mountain ranges rose as crustal blocks. Phase one rocks were thrust over phase two rocks as a result of reverse faults. This resulted in the formation of the Central Rocky Mountains. Subsequently, this rising caused the lowering of the basins which contained accumulated sediments. This erosion surface was sub dived into two categories based on their geographical steam drainage by Steven et al. (1997). While one drained south eastward, the other drained north eastward. This points out that the epeirogen was active and that is why the hypothesis is considered to be significant. Another experiment conducted by Kelley and Chapin (2004) using apatite fission track data found out that the depths of the mountain ranges. The experiment tells us that the depth ranged from 1.4km to 3.85km. As discussed earlier, the Southern Rockies lie between Colorado and the Great plains. These plains are covered with sediments that give them the elevation. What is controversial about the Larimide Orogeny is that geologists find themselves unable to place this orogeny in a conventional tectonic plate. This upliftment was the followed by the period known as Cenozoic. This period marks excessive volcanic activity. Extreme volcanic activity took place in Colorado and New Mexico and great dike systems were formed in connection with several of these intrusions (J.S and S.W Aber Emporia State University 1). As the levels of magma rose into Northern America, arc- shaped ranges came into existence. Today, these are known as the Sierra arcs. For a very long period of time the lava was left to cool down under the ranges. It was later that this solid lava moved towards the Rockies. During the Larimide Orogeny, the volcanic activity shifted westwards once again. The ambiguous question here is about the history of the thick skinned laramide orogeny. There have been two hypotheses for this so far.
It is believed that the angle of the subduction slab encountered a considerable change, extending to the East. This shows us that there as a transportation of crust from the West to the east.
The presence of Mesozoic crust and mantleto depths of 100 km or more under the Sierra Nevada (Ducea and Saleeby, 1996; 1998) suggests that slab shallowing did not occur under the Sierra Nevada, at least not in the manner in which it existed under the Mojave Desert .Cessation of arc magmatism is usually attributed to a slab being too shallow for dehydration reactions to generate fluids (Armstrongand Ward, 1991; English et al., 2003; Gutscher et al., 2000; Humphreys et al., 2003). If the Farallon plate was deep enough under the Sierra Nevada to generate such fluids, why did magmatism cease there? Saleeby (2003) argued that the asthenospheric wedge ceased to bringing undepleted material because shallow subduction to the east interfered with return flow of new asthenosphere (Jones p12). This is where the second hypothesis comes in.
The other hypothesis was that there was no slap beneath North America. Instead, the laramide orogeny as the result of tension that through the lithosphere. The first hypothesis has a lot of problems. If the slab is thought to shallow as buoyant material is subducted, then timing of subduction of this material at the trench conflicts with some events in the continental interior (Jones 16).
Volcanic arcs occur due to the sinking of oceanic plates at a particular angle of subduction. It is said that the Mid- Southern Rockies were formed due to the flattening of this angle of subduction. This led to friction that subsequently caused piling up of rocks and finally, the rising of Rockies. Prior to the ice age, in the Quaternary period, the tectonic activity gradually reduced but the volcanic eruptions remained. Due to these eruptions, there was a major crustal uplift that gave the ranges a rise in their altitude. It is said that, vertically, this rise was for about 1.6km. After this, it was during the ice age that significant activity stopped taking place. The highest peaks of these ranges carry small glaciers.
The rising of the Southern Rockies can be seen in three phases or three uplifts. The third uplift gave rise to the Southern Rockies as a result of collision of tectonic plates. In this process, the angle of subduction became shallow resulting in the underlying oceanic lithosphere (crust) to cause a drag on the overlying continental lithosphere (Nick Oza 1). When rocks of lower strata are pushed above rocks of higher strata, they are called thrust faults. Due to the resistance, one rock piled on top of the other to give rise to the Southern Rockies. There is a general agreement on the fact that the Rockies ere a result of tectonic activities and magmatism. But, there has always been disagreement with the horizontal slab movement.
The terrain in the current Rockies is determined by factors like wind and water. Studies tell us that during the ice age, glaciated terrains accrued to form moraines. The current Rockies, geologists say is the result of deposition of sediments from the first two phases resulting in the constant upliftment of the Rockies. These sediments are visible along the Dakota Hogback ranges. The current Rockies are compared to Tibet. The glacial landforms are the marks that ice age left on Southern Rockies. Today, these glacial landforms are one of the most stunning tourist spots in the world. Stream and river down cutting increased during the period of Pleistocene (J.S and S.W Aber Emporia State University 1). This has been seen to be the result of heavy showers and the running of water down the slopes.
Armour, J., Fawcett, P.J. and Geissman, J.W. 2002. 15 k.y. paleoclimatic and glacial record from northern New Mexico. Geology 30(8):723-726.
Butler, A.P. Jr. 1971. Tertiary volcanic stratigraphy of the eastern Tusas Mountains, southwest of the San Luis Valley, Colorado-New Mexico. In, James, J.L. (ed.), Guidebook of the San Luis Basin, Colorado, p. 289-300. New Mexico Geological Society.
Chronic, H. 1980. Roadside geology of Colorado. Mountain Press Publ. Co., Missoula, Montana, 334 p.
Colorado Geologic Highway Map. Published by GTR Mapping with cooperation of the Colorado Geological Survey. Revised edition 1991; reprinted 1998.
Dethier, D.P. 2001. Pleistocene incision rates in the western United States calibrated using Lava Creek B tephra. Geology 29, p. 783-786.
Emery, P.A. 1971. Water resources of the San Luis Valley, Colorado. In, James, J.L. (ed.), Guidebook of the San Luis Basin, Colorado, p. 129-132. New Mexico Geological Society.
Fan, M., Heller, P. Allen, S.D. and Hough, B.G. 2014. Middle Cenozoic uplift and concomitant drying in the central Rocky Mountains and adjacent Great Plains. Geology 42/6, p. 547-550.
Johnson, R.B. 1971. The Great Sand Dunes of southern Colorado. In, James, J.L. (ed.), Guidebook of the San Luis Basin, Colorado, p. 123-128. New Mexico Geological Society.
Knepper, D.H. Jr. and Marrs, R.W. 1971. Geological development of the Bonanza-San Luis Valley-Sangre de Cristo Range area, south-central Colorado. In, James, J.L. (ed.), Guidebook of the San Luis Basin, Colorado, p. 249-264. New Mexico Geological Society.
Lindsey, D.A. 1995. Geologic map of the Cuchara Quadrangle, Huerfano County, Colorado. U.S. Geological Survey, Miscellaneous Field Studies, Map MF-2283.
Lindsey, D.A. 1996. Reconnaissance geologic map of the Cucharas Pass Quadrangle, Huerfano and Las Animas counties, Colorado. U.S. Geological Survey, Miscellaneous Field Studies, Map MF-2294.
Lipman, P.W. and Steven, T.A. 1971. Reconnaissance geology and economic significance of the Platoro Caldera, southeastern San Juan Mountains, Colorado. In, James, J.L. (ed.),Guidebook of the San Luis Basin, Colorado, p. 221-230. New Mexico Geological Society.
Penn, B.S. and Lindsey, D.A., 1996, Tertiary igneous rocks and Laramide structure and stratigraphy of the Spanish Peaks region, south-central Colorado: Road log and description from Walsenburg to La Veta (first day) and La Veta to Aguilar (second day), Colorado. U.S. Geological Survey, Open-file report 96-4.
Peterson, R.C. 1971. Glaciation in the Sangre de Cristo Range, Colorado. In, James, J.L. (ed.), Guidebook of the San Luis Basin, Colorado, p. 165-167. New Mexico Geological Society.
Ray, L.L. 1940. Glacial chronology of the southern Rocky Mountains. Geological Society America, Bulletin 51, p. 1851-1917.
Richmond, G.M. 1965. Glaciation of the Rocky Mountains. In, Wright, H.E. Jr. and Frey, D.G. (eds.), The Quaternary of the United States, p. 217-230. Princeton University Press, Princeton, New Jersey.