PowerPoint PresentationQuestions to ponderRegional Mountain buildingSlide 4SubductionSlide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Lect 19Convergent Boundaries: Origin of MountainsQuestions to ponderQuestions to ponder•What is an orogeny?•What tectonic scenarios lead to mountain building?•What type of evidence (rocks, minerals, structures) suggests mountain building in the past?•What are the parts of a subduction zone?Regional Mountain buildingRegional Mountain building•Orogeny – mountain building event.•Convergence!•Volcanism•Collision•Note: Local mountains can be built from other causes!Most terrestrial mountains are built at convergent plate tectonic boundariesThere are three subcategories of convergent boundaries:A) Subduction1. Oceanic - Oceanic2. Oceanic – ContinentalB) Collision3. Continental – ContinentalEach of these three types have certain major features in commonConvergenceSubduction•Subduction – two types of mountain building•volcanic island arc–Oceanic plate subducted under another oceanic plate•continental volcanic arc–Oceanic plate subduction under continental plateConvergent subduction zones can be roughly divided into four major regions that include:Volcanic arcDeep-ocean trenchForearc regionBackarc regionA. Subduction ZonesWhen two oceanic plates converge, one is subducted beneath the other, causing partial melting in the mantle wedge above the plateVolcanic ArcVolcanic Island ArcsIn the forearc region, pyroclastic materials from the volcanic arc as well as sediments from the land mass collectAdditional sediments scrapped off the subducting plate are added to the forearc regionForearcAnother area where sediments and volcanic debris can accumulate is in the backarc region Here, tensional forces dominate, causing the crust to be stretched and thinnedBackarcThese tensional forces are caused by trench rollback This can create rifting and eventually lead to seafloor spreading in the backarc regionRifting in the BackarcThe backarc region maybe active or passiveIn an active backarc region, rifting and maybe seafloor spreading is occurringIn a passive backarc region, the rifting is currently not activeThe Tonga Trench backarc is activeThe Japanese Islands backarc is passiveActive & Passive Backarc ZonesThe Lau Basin is a backarc basin located west of the north-south trending Tonga TrenchAs shown on the map, the East Lau Spreading Center is a small, young seafloor spreading ridge, which is currently activeActive Backarc ZonesThe backarc spreading that formed the Sea of Japan is thought to have rifted a small piece of continental crust from AsiaPassive Backarc ZonesSeafloor spreading formed the ocean crust of the Sea of JapanCurrently, the spreading is not activeAn example is the island arc in the Caribbean SeaVolcanic Island ArcsBuilding of volcanic arcsEmplacement of plutonsDevelopment of an accretionary wedgeForearc basinsContinental Volcanic ArcsAs an oceanic plate descends into the mantle, increasing temperature and pressure drives water-rich fluids from the rockBuilding Volcanic ArcsThick continental crust greatly impedes the ascent of magmaA high percentage of magma that intrudes the crust never reaches the surfaceEmplacement of PlutonsInstead it crystallizes at depth to form plutonsPlutonEmplacement of PlutonsThe accretionary wedge is a chaotic mixture of sediments, washed in from the continent and scrapped off of the subducting oceanic plate, that accumulate above the trench and the forearc basinAccretionary WedgeThe accretionary wedge can evolve into a complex structure of faulted and folded sedimentary rocks and scraps of the oceanic plate, all intermixed with metamorphic rocksAccretionary WedgeFaulted and folded accretionary wedge material exposed along the Barbados coastlineThis profile shows the complex structure of the Nankai accretionary wedge, JapanAs the accretionary wedge is uplifted, it tends to act as a barrier to the movement of sediments from the continent to the trenchAs a result, these sediments collect between the volcanic arc and the accretionary wedgeA horizontal sequence of sedimentary strata up to several kilometers thick can accumulateForearc BasinThe Sierra Nevada Mountains, the San Joaquin Valley and the Pacific Coast Range are major geologic features in CaliforniaCalifornia OrogenyThe Pacific Coast Range is the remnant of an accretionary wedgeThe geology of the Pacific Coast Range is a complex mixture of continental sediments, metamorphic rock and fragments of ocean floor crustPacific Coast RangeWhen two continents collide head on, it can result in the formations of major mountain rangesB. When Continents CollideContinental collision starts from subductionWhen two continental masses converge, the deep-ocean trench becomes filled with continental rockThe continental rock is less dense and more buoyant and will not subduct!Contiental collision from subductionContinental CollisionsAfter the oceanic crust was consumed, continental crust collided resulting in upliftHimalayasAn oceanic plate was being subducted under the southern margin of the continent of AsiaA deep-oceanic trench ran along the subduction zone and a well-developed continental volcanic arc had formed on the Asian continentIndia and Asia CollideIt is the compressional forces from the collision that cause the once flat sedimentary beds to be folded and uplifted; faulted and metamorphosedIndia and Asia CollideThe shortening and thickening of the crust, combined with folding and faulting, created the spectacular HimalayasIndia and Asia CollideThe formation of the Himalayas was followed by uplift that created the Tibetan PlateauIndia and Asia CollideMount Everest is capped with marine limestone!The collision between India and Asia slowed but did not stop the northward movement of IndiaIndia has now penetrated 2000 kilometers (1200 miles) into Asia, and is still moving northIndia and Asia CollideThis continued movement of India deformed much of Indochina and parts of China that is squeezed eastward out of the collision zoneThe Appalachian Mountains occur along the eastern margin of North America and extend from Alabama north to New England and beyond into