Plate Tectonics PDF: Earth Science

- ST01502 EARTH SCIENCE - ▪ Plate tectonics – theory that describes the movements of earth’s plates. The lithosphere is divided to pieces called plates which float on hot, deformable asthenosphere, moving in various directions, spreading apart, slowly colliding and grinding past one another....

- ST01502 EARTH SCIENCE - ▪ Plate tectonics – theory that describes the movements of earth’s plates. The lithosphere is divided to pieces called plates which float on hot, deformable asthenosphere, moving in various directions, spreading apart, slowly colliding and grinding past one another. ▪ Plate made up of large blocks of lithosphere that is stiff & rigid. ▪ Plate tectonics help in explaining how earth works as a system, forming connections between rock cycle, carbon cycle, the rise and decline of mountains, emplacement of important economic ore deposits and the locations of continents, oceans, mountains, volcanoes & earthquakes. https://www.youtube.com/watch?v=RA2-Vc4PIOY ▪ Major plates: 7 major plates (> 20 million km 2 ) (i) Pacific, (ii) North American, (iii) Eurasian, (iv) African, (v) Antarctic, (vi) Indo-Australian and (vii) South American. ▪ Minor plates (20 million km 2 – 1 million km2), microplates (< 1 million km2).  (iii) (ii) (iv) (vi) (i) (vii) (v)  The driving force behind plate tectonics is convection in the mantle. Hot material near the Earth's core rises, and colder mantle rock sinks. The convection drive plates tectonics through a combination of pushing and spreading apart at mid-ocean ridges and pulling and sinking downward at subduction zones. Forces that involve in moving the lithosphere: ▪ Ridge push – at mid-ocean ridge, the young lithosphere sits atop a topographic high. The downward pull of gravity will induce the lithosphere to slide down the gentle slopes of the ridge, pushing against the thicker lithosphere beneath the flat abyssal floor. ▪ Slab pull – at subduction zone, the cold, dense slab is free to sink into the mantle, sliding down a dipping trajectory beneath the overriding plate. As the slab descends, it pulls the rest of the lithosphere into the oceanic trench behind it. ▪ Friction – this force is exerted by the viscous mantle rock that borders the lithosphere. Slab friction drags the top, bottom & the leading edge of descending lithosphere in the subduction zone. Plate friction drags elsewhere at the base of the plate.  Ridge push Slab pull Slab pull https://www.youtube.com/watch?v=kwfNGatxUJI  ▪ The concept of plate tectonics was born in late 1960’s by combining 2 pre-existing ideas: 1. Continental drift – idea that continents move 2. Seafloor spreading – hypothesis that the seafloor forms freely over earth’s surface, changing their at the crest of mid oceanic ridge, then moves horizontally positions relative to one another. away from the ridge crest toward an oceanic trench. ▪ Continents can be made to fit together like pieces of a picture puzzle → similarity of Atlantic coastlines of Africa & S America. ▪ Early 1900s, Alfred Wegener, a German meteorologist, made a strong case for continental drift → S America, Africa, India, Antarctica and Australia had almost identical late Paleozoic rocks and fossils. ▪ The plant Glossopteris is found in Pennsylvanian & Permian age rock on all 5 continents, and fossil remains of Mesosaurus a freshwater reptile found in Permian-age rocks only in Brazil and S Africa. Fossil remains of Lystrosaurus and Cynognathus found in Triassic-age rocks on all 5 continents. ▪ Wegener reassembled the continents to form a giant supercontinent, Pangaea. ▪ Pangaea separated into 2 parts: (i) Laurasia the northern supercontinent containing what is now North America and Eurasia. (ii) Gondwanaland the southern supercontinent composed of all the present day southern hemisphere continents and India. ▪ Recent evidence of continental drift by paleomagnetic evidence → distinctive rock contacts and isotopic ages of rocks matched S America and Africa. Other evidence is rocks in Brazil and rocks in Gabon (Africa) that are similar in type, structure, sequence, fossils, ages, and degree of metamorphism. ▪ Harry Hess, a geologist in Princeton University, proposed that the seafloor might be moving too. ▪ Initial concept – the seafloor is moving like a conveyer belt away from the crest (spreading axis) of the mid-oceanic ridge, down the flanks of the ridge, and across the deep-ocean basin, to disappear finally by plunging beneath a continent or island arc (subduction). ▪ Hess’s original hypothesis – seafloor spreading is driven by deep mantle convection. Convection is a circulation pattern driven by the rising of hot material and/ or the sinking of cold material. Hot material has a lower density, so it rises; cold material has a higher density and sinks. https://www.youtube.com/watch?v=DZL5GWaLviY ▪ Magnetometer surveys at sea shows most magnetic anomalies at sea are arranged in bands that lie parallel to the rift valley of the mid oceanic ridge. Alternating positive and negative anomalies form a stripe-like pattern parallel to the ridge crest. 1. Subduction zones, or convergent margins. 2. Divergent margin, two plates are spreading apart, as at seafloor- spreading ridges or continental rift zones such as the East Africa Rift. 3. Transform margins mark slip-sliding plates, such as California's San Andreas Fault, where the North America and Pacific plates grind past each other with a mostly horizontal motion. https://www.youtube.com/watch?v=3yD7jmHcdVc  plate (judi mountain of volcanoes ↓ I belangger 1. Convergent boundaries: where two plates are colliding. Subduction zones occur when one or both of the tectonic plates are composed of oceanic crust. The denser plate is subducted underneath the less dense plate. The plate being forced under is eventually melted and destroyed. i.Where oceanic crust meets ocean crust ▪ Island arcs and oceanic trenches occur when both of the plates are made of oceanic crust. Zones of active seafloor spreading can also occur behind the island arc, known as back-arc basins. These are often associated with submarine volcanoes. ii.Where oceanic crust meets continental crust ▪ The denser oceanic plate is subducted, often forming a mountain range on the continent. The Andes is an example of this type of collision. iii.Where continental crust meets continental crust ▪ Both continental crusts are too light to subduct so a continent-continent collision occurs, creating especially large mountain ranges. The most spectacular example of this is the Himalayas.  plate moving apart I 2. Divergent boundaries –where two plates are moving apart. The space created can also fill with new crustal material sourced from molten magma that forms below. Divergent boundaries can form within continents but will eventually open up and become ocean basins. roubles form within continents topi not terburn judi ocean basin i. On land - > jadi riff valleys ▪ Divergent boundaries within continents initially produce rifts, which produce rift valleys. ii. Under the sea > - mid-oceanic ridges ▪ The most active divergent plate boundaries are between oceanic plates and are often called mid-oceanic ridges.  each other. passed I ▪ 3.Transform boundaries –where plates slide passed each other. ▪ The relative motion of the plates is horizontal. They can occur underwater or on land, and crust is neither destroyed nor created. ▪ Because of friction, the plates cannot simply glide past each other. Rather, stress builds up in both plates and when it exceeds the threshold of the rocks, the energy is released –causing earthquakes. ↓ & ferlebih threshold sebabhan ada stress btw plates Ada 3 boudies. bath recessed and causing gempabami ① convergent , energy ② divergent ③ Transform