Week 5: Orogens and Mountain Building

• What are orogens


  • Orogens are mountain building events that occur when two portions of the Earth’s crust are compressed together
  • Orogenic mountain belts lead to the formation of tall mountains and often display folded, metamorphosed and faulted rocks as well as shear zones and intrusions
• Examples of Orogens

  • Orogens can be formed by collisional events, such as the Himalayas or subduction events such as the Andes
  • The progression of orogens is dependent on many different factors but they typically undergo periods of accretion, uplift, culmination and erosion
• The Himalayan Orogen

  • The Himalayan orogen is formed via continental collision between Asia and India. This collision, has led to the accumulation of crustal material. The accumulation of under thrusted material contributes to crustal thickening
  • The Himalayas also experiences uplift. The surface uplift of this orogen is primarily contributed to by the continued convergence of the tectonic plates as well as isostatic uplift.
• What is isostatic uplift

  Isostatic uplift is a gravitational equilibrium response when eroded material reduces the weight on a region of crust, in response to this the crust lifts up, which contributes to surface uplift
• Tibetan Plateau formation

  Combination of various processes over geological time
• Mechanisms of Tibetan Plateau formation

  1. Isostatic uplift

  2. Crustal thickening: Continuous under thrusting of Indian continental crust contributes to the thickening of the crust

  3. Mantle upwelling: The rise in hot mantle material under the thick crust of the mountain belt, may result in a thinning of the crust -> isostatic response

  4. Crustal delamination: When lower, denser material of the crust breaks off, there is a decreased GPE -> isostatic response