Mountain building shapes Earth's surface through tectonic collisions, creating folded and faulted rocks. This process involves uplift, metamorphism, and isostatic adjustment, forming iconic ranges like the Himalayas and Andes.

Continents grow through accretion, adding new material at plate boundaries. Stable cratons form continental cores, while terranes and mountain belts like cordilleras contribute to landmass expansion. These processes sculpt Earth's ever-changing landscape.

Orogenic Processes

Formation and Deformation of Mountain Ranges

• Orogeny, the process of mountain building through tectonic plate collisions and convergence
  • Involves uplift, folding, faulting, and metamorphism of rocks
  • Examples include the formation of the Himalayas and the Andes
• Folding occurs when rock layers are compressed and bent into wave-like shapes
  • Anticlines are upward-arching folds (Grand Staircase-Escalante National Monument)
  • Synclines are downward-curving folds (Sideling Hill road cut in Pennsylvania)
• Faulting involves the fracturing and displacement of rock layers along a fault plane
  • Normal faults form when the hanging wall moves down relative to the footwall (Basin and Range Province in the western United States)
  • Reverse faults occur when the hanging wall moves up relative to the footwall (Rocky Mountains)
  • Strike-slip faults have horizontal movement of rock layers (San Andreas Fault in California)

Metamorphism and Isostatic Adjustment

• Metamorphism is the transformation of rock under high temperature and pressure conditions without melting
  • Regional metamorphism occurs over large areas during mountain building events (Barrovian metamorphism in the Scottish Highlands)
  • Contact metamorphism happens when magma intrudes and heats surrounding rock (Skiddaw Granite in the Lake District, England)
• Isostasy is the gravitational equilibrium between Earth's crust and mantle
  • When mountains form, the crust thickens and becomes more buoyant, causing uplift (Tibetan Plateau)
  • As mountains erode, the crust becomes thinner and denser, leading to subsidence (Appalachian Mountains)

Continental Growth

Accretion and Terrane Addition

• Accretion is the process of adding new material to continents through the collision and amalgamation of tectonic plates and terranes
  • Occurs at convergent plate boundaries, such as subduction zones and continental collisions
  • Examples include the accretion of island arcs and microcontinents to North America's western margin
• Terranes are fault-bounded crustal blocks with distinct geologic histories that have been accreted to continents
  • Can include island arcs, seamounts, continental fragments, and accretionary wedges
  • The Wrangellia Terrane in western North America is a well-studied example

Cratons and Continental Stability

• Cratons are stable, ancient cores of continents that have remained relatively undeformed for billions of years
  • Composed of Precambrian crystalline basement rock, often covered by younger sedimentary layers
  • Examples include the Canadian Shield, the Siberian Craton, and the Kaapvaal Craton in South Africa
• Cratons form the nucleus around which younger terranes and sedimentary basins accumulate
  • Provide a stable foundation for continental growth and the development of extensive sedimentary cover
  • Act as rigid blocks during later tectonic events, influencing the deformation of surrounding regions

Mountain Belts

Cordilleran Orogens

• Cordillera refers to a linear chain of mountains formed along a convergent plate boundary, typically associated with subduction zones
  • Characterized by a series of parallel mountain ranges, volcanic arcs, and associated basins
  • The North American Cordillera extends from Alaska to Mexico and includes the Rocky Mountains, the Sierra Nevada, and the Cascade Range
• Cordilleran orogens develop through the accretion of terranes, the formation of magmatic arcs, and the deformation of sedimentary basins
  • Subduction of oceanic crust beneath a continental margin leads to the growth of a volcanic arc and the formation of an accretionary wedge (Andes Mountains)
  • Collision of an oceanic plateau or microcontinent with the margin can result in the obduction of ophiolites and high-pressure metamorphism (Coast Mountains of British Columbia)