Mountain Building - Orogenesis

1. Mountain Building - Orogenesis

2. Archimedes’ principle • The mass of the water displaced by the block of material equals the mass of the whole block • Thus for a material with a lower density than water, the proportion of material above the water surface is constant • For example wood (density 0.8 gm/cm) will have 20% of its mass above water (density of 1.0 gm/cm). Thus for a 1 m block 0.2 m will be above water and 0.8 m below, but for a 2 m block .4 m will be above water and 1.6 m below Fig. 6.28

3. Isostasy Fig. 6.30

4. Isostasy & Mountain Roots • Continental Crust has “roots” • As a result of isostacy, the thicker the surface exposure of rock, the thicker the crustal “roots” • As continental crust is compressed it shortens and thickens • Avg. continental crust is 35-40 km thick, under deformed crust avg. is 50-70 km, with the majority of the difference in the “roots” Fig. 6.29

5. Isostasy & Mountain Roots Fig. 6.31

6. Class Assignment Place the following in the appropriate location on the concept map. Not all terms will be included and each may be used only once. a) volcanoes b) Normal faults c) Transform boundary d) Folds e) Convergent boundary f) Mountains g) Hot spots h) Divergent boundary i) Tension stress j) Compression stress k) Shear stress l) Reverse faults 1 Occur at Occur along Occur along 3 2 4 Creating Creating Magma Produces 5 7 6 Resulting in Resulting in Resulting in 10 8 9

7. Mountain-Types • Fault-Block Mountains • Formed from tensional stress • Normal Faulting • Example: Basin and Range Provinces SW USA

8. Mountain-Types • Upwarped Mountains • Formed from compressional stress • Broad arching of the crust or great vertical displacement along faults • Example: Black Hills SD

9. Mountain-Types • Folded Mountains • Formed from compressional stress • Reverse Faulting and Folding – highly deformed rocks • Will have highly metamorphosed rocks • Example: Appalachians, Himalayas

10. Mountain-Types • Volcanic Mountains • Formed volcanic activity • Associated with plate boundaries or hot spots • Example: Cascade Mts. Or mountains within Japan

11. Mountain Building (Orogenesis) Zones Convergence Zones Continental Collision Continental Rifting

12. Convergence Zones • Oceanic-Continental • Folded Mt. Belts • Thrust Faults • Volcanic Chains • Accreted Terranes • Example: Andes Mountains, Cascades

13. Accreted Terranes • As exotic blocks collide with continents they become sutured to the continent. • The blocks are referred to accreted terranes • Accreted Terranes are island arcs, portions of ocean floor, fragments of continental crust

14. Convergence Zones • Oceanic-Oceanic • Volcanic Chains • Examples: Japan, Philippines

15. Collision Zones • Folded Mt. Belts • Thrust Faults • Remnants of Volcanic Chains • Examples: Alps, Himalayas

16. Continental Rifting • Fault-block mountains

17. Mountain Building – Multiple Events Example: Appalachian Mountains

18. Mountain Building, Rock Cycle and Plate Tectonics

19. Why does the Earth have mountains of various height? • Erosion attacks mountains – remember Earth wants to be flat • Orogenic collapse.