Lesson 19

Lesson 19 - Module E Planetary Engineering Mesozoic...

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Module E. Planetary Engineering: Mesozoic Tectonics Lesson 19: Mountain Belts Introduction Mountain belts exert a major influence on landscapes, climate, and migration patterns of surface-dwelling species. The formation, extent, and nature of mountain belts is entirely controlled by tectonics! 24% of the Earth's land mass is mountainous. And, as shown below in the map of the topography of both land and ocean surfaces, areas of high relief (mountainous regions) dominate our entire region in western North America and most of Asia. Figure E-32. Topographic Map of the Earth Some of the major mountain belts on the Earth are the A: North American Cordillera, B: Appalachians, C: Caledonian Belt, D: Andes, E: Urals, F: Himalaya, G: Alps, and H: the Tasman Belt. The legend shows the relationship between color and elevation. The Earth's major mountain systems are generally colored orange to red to grey. Image from NOAA National Geophysical Data Center . Mountain building, or orogeny is usually the result of the movement of lithospheric plates. In geology, an orogenic belt (i.e. a mountain belt) could also refer to the roots of an ancient mountain belt that has been eroded down. As shown in the map above, mountain belts (or chains of individual mountains) are commonly found along plate margins, specifically convergent margins. There are 4 main mechanisms for the growth of orogenic belts: 1. volcanic activity (usually in volcanic arcs along convergent margins) 2. regions undergoing crustal extension (i.e. normal faulting) 3. regions undergoing crustal shortening due to compression 4. collision between two continental plates
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Volcanic Activity and Orogeny At a convergent margin where oceanic crust is being subducted, the oceanic plate that is sinking down into the upper mantle begins to heat up. Water is driven off the down-going plate, and this water passes up into the overlying wedge of mantle material (see figure below), where it causes that mantle material to start to melt. This melt, or magma, is hot and has relatively low density, so it rises buoyantly into the overlying crust. Figure E-33. Formation of Stratovolcanoes Water released from the subducting oceanic crust rises up and hydrates the overlying mantle; water released deeper down causes partial melting of rock to magma that erupts in the arc volcanoes. Figure from G. Zandt, 2002 ("Earth science: The slippery slope", Nature 417:497-498). A portion of the magma makes its way all the way up through the crust and ultimately erupts on the surface, eventually building large volcanoes. In a magmatic arc such as this, the volcanoes are typically quite widely spaced (10s to 100s km apart), so this process does not produce a continuous mountain belt, but rather a chain of isolated volcanoes. Stratovolcanoes and the Pacific Ring of Fire
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This note was uploaded on 11/18/2011 for the course EOSC 116 taught by Professor Randell during the Winter '09 term at UBC.

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Lesson 19 - Module E Planetary Engineering Mesozoic...

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