7a. Orogeny - Mountain Building
advertisement
9. Mountains and Mountain Ranges • Orogeny – the process of mountain building – Crustal thickening • Subduction zones • Sub-plate magmatic activity • Continental collision • Compressive forces “squeeze” crust together – Thickening leads to isostatic adjustment • Rising of less-dense continental crust • Rising increases erosion, redistributes mass © Cengage Learning 2015 © Cengage Learning 2015 Island Arcs • Island arcs – volcanic mountain chain – Ocean-ocean convergent zone – Subduction complex – “squeegeed” sediments and fractured rock – Underthrusting – subduction complex grows from bottom, forced up – Forearc basin – down dip area between arc and complex © Cengage Learning 2015 © Cengage Learning 2015 The Andes • Subduction at a continental margin • Rising magma – Some rises to form volcanoes – Some cools inside forming plutons – Thickening crust leads to isostatic rise • Once thick enough, soft rock beneath oozed outwards creating thrust faults • Foreland basin – Filled with sediments eroding from risen landscape © Cengage Learning 2015 © Cengage Learning 2015 © Cengage Learning 2015 © Cengage Learning 2015 © Cengage Learning 2015 The Himalayas • Collision between continents • Oceanic lithosphere between two continents “used up” – then collision between continents – Both continental crust, neither can sink. – India thrusts beneath Asia, crustal thickness doubles © Cengage Learning 2015 © Cengage Learning 2015 © Cengage Learning 2015 © Cengage Learning 2015 © Cengage Learning 2015 © Cengage Learning 2015 © Cengage Learning 2015 © Cengage Learning 2015 The Himalayas Today • Today the Himalayas: – Contain all three rock types – Many sedimentary rocks from old sea-floor – Plateau approx. 4000 m; mountains rise from this – Crustal mass caused faulting as it spread • Extensional (normal) faults in mountains • Compressional (reverse/thrust) faults in foothills – India is still moving north – The Alps, Urals, and Appalachians all happened under similar circumstances © Cengage Learning 2015 Mountains and Earth Systems • Mountains rise due to tectonic forces – Interact with hydrosphere, atmosphere, biosphere • Air rises over mountains – Moisture rains out • Rise of Himalayas coincides with global cooling period • Soil erosion can be a problem for human habitation in mountains © Cengage Learning 2015 © Cengage Learning 2015
