Ch14_Outline

Ch14_Outline - 1 Chapter 14 Convergent Boundaries: Mountain...

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Unformatted text preview: 1 Chapter 14 Convergent Boundaries: Mountain Building and the Evolution of Continents Mountain building Mountain building has occurred during the recent geologic past American Cordillera the western margin of the Americas from Cape Horn to Alaska which includes the Andes and Rocky Mountains Alpine-Himalayan chain Mountainous terrains of the western Pacific Mountain building Older Paleozoic- and Precambrian-age mountains Appalachians Urals in Russia Orogenesis the processes that collectively produce a mountain belt Includes folding, thrust faulting, metamorphism, and igneous activity 2 Mountain building Orogenesis the processes that collectively produce a mountain belt Compressional forces producing folding and thrust faulting Metamorphism Igneous activity Mountain building Several hypotheses have been proposed for the formations of Earths mountain belts With the development of plate tectonics it appears that most mountain building occurs at convergent plate boundaries Earths major mountain belts Figure 14.3 3 Convergence and subducting plates Major features of subduction zones Deep-ocean trench region where subducting oceanic lithosphere bends and descends into the asthenosphere Volcanic arc built upon the overlying plate Island arc if on the ocean floor or Continental volcanic arc if oceanic lithosphere is subducted beneath a continental block Convergence and subducting plates Major features of subduction zones Forearc region is the area between the trench and the volcanic arc Backarc region is located on the side of the volcanic arc opposite the trench Convergence and subducting plates Dynamics at subduction zones Extension and backarc spreading As the subducting plate sinks in creates a flow in the asthenosphere that pulls the upper plate toward the trench Tension and thinning may produce a backarc basin 4 Convergence and subducting plates Dynamics at subduction zones Compressional regimes Occurs when the overlying plate advances towards the trench faster than the trench is retreating due to subduction The resulting compressional forces shorten and thicken the crust Subduction and mountain building Island arc mountain building Where two ocean plates converge and one is subducted beneath the other Volcanic island arcs result from the steady subduction of oceanic lithosphere Continued development can result in the formation of mountainous topography consisting of igneous and metamorphic rocks Volcanic island arc Figure 14.4A 5 Subduction and...
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Ch14_Outline - 1 Chapter 14 Convergent Boundaries: Mountain...

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