Mountain Building: From Earthquakes to Geologic Deformation

Mountain ranges are the most spectacular manifestation of continental dynamics. The fact that some mountain ranges were able to maintain their topography over tens of millions years, while their erosion was feeding large sedimentary basins, is unambiguous evidence that tectonic forces can cause sustained uplift of subsidence of the continental crust. Geologists noticed quite early on that most mountain ranges are contractional orogens, the result of horizontal contraction of the continental crust, and that they tend to form long belts separating domains with often quite different geologic history (e.g., Argand, 1924 and Willis, 1891). A tour of active mountain ranges on earth today shows that contractional mountain ranges can arise in a variety of contexts. Some have formed along converging plate boundaries as the result of collisions that can involve two continents (along the Himalayas, e.g., as detailed in this chapter), a continent and an island arc (in Taiwan, e.g., Malavieille et al., 2002a), or a continent and an oceanic plateau (the Southern Alps of New Zealand, e.g., Walcott, 1998). Contractional mountain ranges can also form along subduction zones without necessarily having such collisional features. In the Andes, for example, the stresses transmitted across a subduction zone appear to be sufficient to cause trench-perpendicular shortening (e.g., Lamb, 2006), probably because high heat flow in the back-arc zone weakens the continental lithosphere (Hyndman et al., 2005). Mountain ranges are thus often closely associated with converging plate boundaries. However, active mountain building can also occur far away from plate boundaries, the Tian Shan, in central Asia, being an outstanding example (e.g., Avouac et al., 1993 and Hendrix et al., 1992)