Mountain Building - Orogenesis

Archimedes’ principle Fig –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 Isostasy

Isostasy & Mountain Roots Fig –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 km thick, under deformed crust avg. is km, with the majority of the difference in the “roots”

Fig Isostasy & Mountain Roots

Class Assignment Occur along Creating Resulting in Occur at 3 Magma Produces 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

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

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

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

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

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

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

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

Convergence Zones Oceanic-Oceanic –Volcanic Chains –Examples: Japan, Philippines

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

Continental Rifting Fault-block mountains

Mountain Building – Multiple Events Example: Appalachian Mountains

Mountain Building, Rock Cycle and Plate Tectonics

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