2 Vocabulary Orogenesis Lithosphere Accretion Oros—mountain Genesis—to come into beingLithosphereThe rigid outer layer of Earth, including the crust and upper mantleAccretionthe increase in size of a tectonic plate by addition of material along a convergent boundary
3 Crustal Uplift Evidence Isostasy Marine fossils often found in high elevations in mountainsTerraces hundreds of meters above sea levelIsostasyA floating crust in gravitational balanceExample: blocks of wood floating in waterMountain belts stand higher above the surface of the Earth and have roots that extend deeper into the supporting material below.Crustal thicknesses for some mountain chains are twice as much as the average for the continental crust
4 Crustal UpliftCrust beneath the oceans is thinner than that beneath the continentsOceanic rocks are denser than continental rocks**adding weight to the crust makes it subside**when weight is removed, crustal uplifting occurs (ex.: cargo ship)
5 Crustal Uplift Isostatic Adjustment Ice Age glaciers added weight to the continents, making them downwarp by hundreds of metersWhen glaciers melted, uplift occurredErosion of mountains causes uplift, also
6 Rock Deformation Elastic deformation Plastic deformation When stress is applied, rocks bend, but will snap back if the stress is relievedPlastic deformationWhen the elastic limit is surpassed, rocks deform plastically or break (earthquakes)They are permanently altered through folding and flowing
7 Rock Deformation Folds When flat-lying sedimentary and volcanic rocks are bent into a series of wavelike undulationsExample: pushing on one edge of a carpet until it foldsAnticlineUpfolding or arching of rock layersSynclineDownfolds, or troughs
8 Rock Deformation Dome Basin When upwarping produces a circular or somewhat elongated structureBasinWhen downwarping produces a circular or somewhat elongated structure
9 Rock Deformation Faults and Joints Fractures in the Earth’s crust Dip-slip faultsVertical movementHanging wall—rock that is higher than the fault surfaceFootwall—rock that is lower than the fault surfaceNormal—hanging wall moves downward relative to the footwallReverse—hanging wall moves upward relative to the footwallThrust faults—have a very low angle
10 Rock Deformation Strike-slip faults The dominant displacement is along the strike or trend, of the fault (horizontal)Transform faults—associated with plate boundariesOblique-slip faults—both vertical and horizontal movementTensional forces—pull the crust apartGraben—central block bounded by normal faults; drop as the plates separateHorsts—upfaulted structures that are adjacent to grabenCompressional forces—sections of crust are displaced toward one another
11 Rock Deformation Joints Fractures along which no appreciable displacement has occurredColumnar joints form when igneous rocks cool and develop shrinkage fractures, producing elongated, pillarlike columnsSheeting produces a pattern of gently curved joints that develop more or less parallel to the surface of large exposed igneous bodies.
12 Mountain Types Fault-block mountains Tensional stresses elongate and fracture the crust into numerous blocks. Movement along the fractures tilt the blocks producing parallel mountain ranges.
13 Mountain Types Folded mountains (complex mountains) Upwarped mountains Caused by a broad arching of the crust or because of great vertical displacement along a high-angle faultVolcanic mountains
14 Mountain Building Convergent boundaries Volcanic arcs are forming in most modern-day subduction zonesAleutian-type subduction zones occur where two oceanic plates converge
15 Mountain Building Andean type subduction zones Passive continental margin—part of the same plate as the adjoining oceanic crustBecomes active—subduction zone forms and the deformation process beginsThe oceanic plate descends and becomes magma while there is an accumulation of sedimentary and metamorphic rocks along the subduction zone (accretionary wedge)
16 Mountain Building Continents converge Continental lithosphere is too buoyant to undergo subduction, a collision eventually resultsExample: India colliding with the Eurasian plate
17 Mountain Building Mountain Building and Continental Accretion Smaller crustal fragments collide and accrete to continental marginsExample: mountainous regions rimming the PacificAs oceanic plates move, they carry with them embedded oceanic plateaus or microcontinentsThe upper portions of these thickened zones are peeled from the descending plate and thrust in relatively thin sheets onto the adjacent continental block.This increases the width of the continentTerrane—accreted crustal blocks