Formation of Geologic feature
Formation of Geologic feature
Geologic processes often leave us with magnificent formations. Canyons, Mesas, mountains and volcanoes all give people a sense of aesthetic pleasure. One of the most arresting formations is that of Shiprock peak, located in New Mexico, United States. The Shiprock Peak is found inside the Navajo Indian reservation, in the geologic area known as the four-corners New Mexico Plain. To the northeast, nearly 13 miles, lies the town of Shiprock, New Mexico, named after the formation.
The peak towers from the surrounding plain at about 1,800 feet (550 meters) and has an elevation of 7,178 feet above sea level. The formation has an approximate diameter of 500 meters and is visible for hundreds of miles. Radiating from the peak are 6 linear formations called dikes. The peak was dubbed “shiprock” due to its resemblance to a 19th century Clipper class ship. Prior to that, Captain J. F. McComb referred to it as “needle, while the native Navajos know it as Tse Bit’ A’i or as translated, the Rock With Wings. (Kuss, 2004)
The peak is the center of various myths, legends and rituals of the Navajos. A legend that ties in with the over all geography of the region highlights Shiprock as a pouch bag, carried by a mythical figure known as Goods of Value Mountain, which is composed of the nearby Chuska and Carrizo mountains. Geologic History The Shiprock peak is located inside a geologic field known as the Navajo volcanic field, inside the Four Corners region. The field spans an extensive 20,000 km area that forms a loose quadrilateral with borders sitting inside Utah, Colorado, Arizona and New Mexico.
The Navajo volcanic field is dotted with a myriad of other volcanic structures like dikes, diatremes, and other intrusions. About 30 to 25 million years ago (Oligocene) numerous volcanoes dotted the area. What we see today are eroded remnants of the products of the eruption and extinction of these volcanoes. The Navajo volcanic field is composed of Oligocene-Miocene volcanic structures. The field in itself is situated upon a much more extensive region known as the Four Corners Platform, a part of the Colorado Plateau. The structure of the platform is sequenced by folded sedimentary layers.
It is bounded on both the east and west sides by monoclines approximately Laramide in age. The absence of faults in the region eliminates convergent and divergent faulting as a possible source for the abundance of magma in the area. An explanation for the ascent of magma veins in the Navajo Volcanic Field could be the Laramide fractures allowing for magma seepage. (Foos) Formation and Composition The Shiprock peak is one such remnant of the past volcanic activity in the region. The peak itself is a volcanic plug or neck, the remnant of the central vent system of a prehistoric volcano.
When a volcano becomes extinct, magma contained inside cools and solidifies, producing hard rock. This rock is much harder than the outer surface of the volcano, thus, when exposed to millennia of erosion by wind and water, the outer layers are stripped away, leaving a feature formed by the hardened magma. Other examples of volcanic plugs are the Devil’s tower in Wyoming, Kapsiki Peak in Cameroon and Bass rock, found in Scotland. The Shiprock formation has been stipulated as a product of a maar explosion millions of years ago.
Maar explosions are produced from the meeting of rising magma with groundwater reservoirs, producing steam, which results in accumulation of pressure. Intense explosion occurs, blasting a hole through the surface. The Shiprock peak is classified as a diatreme plug, product of a gaseous explosion that brings up shattered rock called breccia. Although such explosion are generally lacking in lava, the little amount that may be present consists of minette, a type of basalt with high mica content. (Bank, Noblett, Kroeger, & Semken, 2007)
The Shiprock peak is primarily composed of these two substances, conglomerates of breccias and layers of minette. The boulders surrounding Shiprock are composed of tuff-brecia, from the prehistoric explosions. Brecia is formed by shattered rock fragments cemented together by lava. Breccia usually occurs in volcanoes with extremely violent explosions. The material minette is uncommon, being a believed product of slow melting of mantle rock. The presence of minette in Shiprock gives evidence that the magma vein supplying Shiprock may have originated deep in the Earth’s mantle.
(Kuss, 2004) The presence of minette is consistent in the formations within the Navajo Volcanic field. In surrounding parts of the Colorado Plateau however, concentration of the said material is greatly reduced. (Rotzien, 2007) The magma forming Shiprock peak was then about 1 km. beneath the hole, it was only due to differential erosion that the surface has been reduced in its present state, thus exposing the peak, and the surrounding cones and dikes. Aside from the main protuberance, three cones and seven dikes litter the proximity.
The three cones clustered a few hundred meters west of the peak are smaller plugs exposed by the erosion of the surrounding terrain. The largest of the seven dikes has a height of 30 meters and a width of two meters. It extends up to 9 kilometers to the south. (Bank et al. , 2007) The dikes propose the biggest uncertainty to the formation of Shiprock peak. Geologists debate whether the dikes formed after the main pipe, leading to a radial positioning of the dikes, thus supporting an underlying magma chamber.
However, others have argued an alternate scenario. Delaney and Pollard find that ascending dikes seem to be the result of their modeling, implying that such a scenario would not necessitate a central plug and consequently, an underlying magma chamber. (Delaney & Pollard, 1981) They argue that as opposed to the notion that magma wells upward via veins which remain open at the source, magma finds its way to the surface using dike like bodies not directly connected to the magma source. (Muller & Muller, 1980) Conclusion
The Shiprock peak formation is an ideal place for geologists to test and re-test various theories regarding hydrostatic magma flow, magma surfacing and other volcanic processes. Its history and scenery make it one of the most ideal examples of volcanology. Insight into the formation of the Shiprock peak would also in direct extension provide insight on the geologic processes that shaped the are around it, the origin of the Navajo volcanic field, as well as a deeper understanding of the Colorado Plateau. It is now one of the centers by which the debate regarding the role of dikes to magma flow and diatreme formation centers. The magnificence of the formation lies not only with its aesthetic and cultural significance but also with the wealth of knowledge that one may extract from it.
Reference Bank, C. -G. , Noblett, J. , Kroeger, G. , & Semken, S. (2007). Geophysical Investigations of Shiprock and Thumb Igneous Centers, New Mexico. Paper presented at the 20th Annual Keck Symposium. Delaney, P. , & Pollard, D. D. (1981). Deformation of host rocks and flows of magma during growth of minette dikes and breccia-bearing intrusions near Ship Rock, New Mexico, U. S. Geological Survey U. S. Geological Survey, 61. Foos, A. Geology of the Colorado Plateau. Retrieved. from. Kuss, L. (2004). Shiprock [Electronic Version]. Retrieved December 5 2007, from http://www. emporia. edu/earthsci/student/kuss1/shiprock. html Muller, O. H. , & Muller, M. R. (1980). Near surface magma movement. Lunar and Planetary Science Conference, 3, 1979-1985. Rotzien, J. (2007). Magnetic Exploration and Modeling of the Thumb, Navajo Volcanic Field. Paper presented at the 20th Annual Keck Symposium.
University/College: University of Chicago
Type of paper: Thesis/Dissertation Chapter
Date: 29 November 2016
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