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Mountain Building Chapter 11 Stress • Force per unit area on a solid. • Three Main Types: – Tensional Stress – pulls apart – Compressional Stress – squeezes together – Shear Stress – pulls in opposite directions Deformation of Rock • Any change in the original shape and/or size of a rock body. • Affected by: – Temperature – Pressure – Rock Type – Time Deformation of Rock • Two main types: Brittle Deformation: rock will fracture or break. Ductile Deformation: rock will fold or bend. Isostasy • Earth’s crust is floating in gravitational balance on the mantle. • When a change occurs, like erosion, the crust will establish a new level of gravitational balance (Isostatic Adjustment.) • This can cause uplift in the crust. Folds • Wavelike ripples in rock. • Three main types: – Anticlines – upfolds. – Synclines – downfolds. – Monoclines – step-like folds. Faults • Fractures in Earth’s crust where movement has taken place. • 4 main types: – Normal Faults – Reverse Faults – Thrust Faults – Strike-Slip Faults Normal Fault • Hanging wall moves down relative to footwall • Caused by tensional stress. Reverse Fault/Thrust Fault • Hanging wall moves up relative to footwall. • Caused by compressional stress. • Thrust fault has a dip of less than 45o. Strike-slip Fault • Movement is horizontal and parallel to the fault surface. • Caused by shear stress. Mountains • Orogenesis – mountain-building. • Types of Mountains: – Volcanic Mountains – Folded Mountains – Fault-block Mountains • Graben – downwarddisplaced block • Horst – uplifted block Other Landforms • Plateau – high elevation and level surface. • Dome – circular landform produced by upwarping. • Sedimentary Basin – Circular landform produced by downwarping. Convergent Boundary Mountains • Oceanic-Oceanic – forms volcanic mountains. • Oceanic-Continental – forms volcanic and folded mountains. – Accretionary wedge – sediments scraped from the subducting plate. • Continental-Continental – forms complex folded mountains. Mountains at Other Boundaries • Divergent Boundaries – forms fault-block mountains made of volcanic rock. • Non-Boundary Mountains – formed by hot spots or regional extension or stretching. Accretion • When crustal fragments collide with and stay connected to a continental plate. • Terranes – crustal fragments that have a geologic history different from the adjoining fragments.
