How Strong Is The Evidence For A Flat Slab? Research Papers Example
Typically, subduction happens at a relatively steep angle at the point where plate boundaries converge. Nonetheless, subduction also occurs in anomalous shallow angles. Subduction angles that are extremely steep also exist. A flat slab subduction occurs when the lithosphere subducts in a horizontal or a near horizontal manner. This paper looks at different landforms with the aim of determining the strength of the evidence for flat slab subduction.
The Laramide orogeny presents part of the evidence for a flat slab. Through paleomagnetic data, it is shown vast areas of the attached lithosphere and the oceanic crust was subducted during the Laramide orogeny. Dickson and Snynder propose that the subduction of the attached lithosphere and the oceanic crust was horizontal, thereby giving indication of a flat slab. The abrupt subsidence Rocky Mountains region during the Late Cretaceous is also linked to the horizontal subduction.
While these are arguments by other geologists, Bird tests the hypothesis of flat subduction by a quantitative prediction of its effects (Bird 1502). His methodology involves the calculation of the mantel and crust lithosphere displacement, temperature through time and thickness. As Bird writes, the hypothesis of horizontal subductionthat he proposes to test in his articleboth provides a fundamental mechanism for the Laramide orogeny and suggests an explanation for the next eventThe findings from the computational model were compared with actual geological results. Based on the correspondence of the predictions of the model with actual geological data provides sufficient evidence to prove Bird’s hypothesis and the argument of other geologists that a flat slab or horizontal subduction caused the Laramide orogeny (Bird 1507).
Further evidence of a flat slab is presented by Humphreys et al.,. Humphreys et al., acknowledges the argument of a flat slab in the Laramide Orogeny. Humphreys et al., further acknowledges the occurrence of similar behaviors in areas where the Nazca ‘flat-slab’ subducts beneath South America as evidence vindicating the argument of a flat slab (Humphreys et al., 576). However, Humphreys et al., provides a different perspectives on important processes, which in his opinion have remained outside the domain of normal consideration (Humphreys et al., 576). In explaining the Laramide contraction, Humphreys et al., expends the flat-slab model an instead inclines towards the slab de-watering model to explain the decreased density and the resultant uplift in the thick western United States lithosphere.
In their article, Jones et al., acknowledges that recent tectonic studies have presumed that the Farallon plate subducted along the base of North American lithosphere under most of the western United State (Jones 183). Jones et al., argues that the broad flat slab can be used to explain the Laramide orogeny through two of a five element hypothesis. Jones et al., provides an alternative hypothesis that contends that a more limited segment of shallowly subducting slab is created by viscous coupling between the slab (Jones et al., 183). Jones et al., sustains the argument that the favorable comparison with the basement-cored uplifts of the Sierra Pampeanas in Argentina, which are inboard of an inactive segment of the Andean arc and above a shallowly dipping segment of the subducting plate (Jones et al., 187).
Even though alternative hypotheses have been provided to explain landforms that have previously been attributed to the flat slab, there is still strong evidence of a flat slab. Bird et al., using a computational model to calculate the mantel and crust lithosphere displacement, temperature through time and thickness found that his predictions were similar to geological data. This empirical data shows the evidence of a flat slab. Humphreys et al., uses the flat slab model as basis for his hypothesis to further explain landforms in western United States. Jones et al., acknowledges the flat slab subduction as the cause of the Laramide orogeny. This is strong evidence of a flat slab.
Bird, Peter. Formation of the Rocky Mountains, Western United States: A Continuum Computer model. Web. 6 Apr. 2015.
Humphreys, Eugene., Hessler, Erin., Dueker, Kenneth., Farmer, Lang., Erslev, Eric., Atwater, Tanya. How Laramide-age hydration of North American lithosphere by the Farallon Slab controlled subsequent activity in the Western United States. International Geology Review, 45 (2003): 575-595.
Jones, Craig, Farmer, Lang., Sageman, Brad and Zhong, Shijie. Hydrodynamic mechanism for the Laramide orogeny. Geosphere, 7, 1 (2011): 183-201.
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