PLATE TECTONICS PLATE TECTONICS THEORY the dynamics of

PLATE TECTONICS

PLATE TECTONICS THEORY • • • the dynamics of Earth’s outer shell, the lithosphere mountain-building processes Volcanoes earthquakes, evolution of Earth’s surface

Introduction of the Concept • Canadian Geophysicist J. Tuzo Wilson 1966 • Based on hypothesis of continental drift by Wegner 1912

Mantle Layers • • lithosphere asthenosphere. Property Lithosphere Asthenosphere Mechanical Property Cooler & more rigid Hotter & flows more easily Heat Transfer Conduction Convection Adiabatic temperature gradient (temperature that results from a complete combustion process that occurs without any heat transfer or changes in kinetic or potential energy. )

Lithosphere • is broken up into tectonic plates. • seven major and many minor plates.

Crustal material • oceanic crust (7 -10 km thick) • continental crust (2 5 -70 km thick) Source: https: //www. google. com. pk/search? q=plate+tectonics+theory&biw=1366&bih=667&tbm=isch&t b o=u&source=univ&sa=X&ei=v 40 VMKz. OIb. Cs. ASXpo. KIAw&ved=0 CDIQ 7 Ak#facrc=_&imgdii=_&imgrc=IV 0 ju. Lr 7_Q 9 EEM%253 A%3 B Tlpc. YSTx. Xaxq. ZM%3 Bhttp%253 A%252 Facademic. brooklyn. cuny. edu%252 Fgeology%252 Fgr oc ha%252 Fplates%252 Fimages%252 Flithosphere. jpg%3 Bhttp%253 A%252 Facademic. brookly n. cuny. edu%252 Fgeology%252 Fgrocha%252 Fplates%252 Fplatetec 10. htm%3 B 350 Source: https: //www. google. com. pk/search? q=thickness+continental+crust&biw=1366&bih=624&source=l nm s&tbm=isch&sa=X&ei=4 RM 8 VODj. OZTfas. Cgcg. E&ved=0 CAg. Q_AUo. AQ#facrc=_&imgdii=_&imgrc=9 y. Oj. Od. RPn. Kcd 8 M%253 A%3 Bw. BAT 2 Yidp. G 7 OM%3 Bhttp%253 A%252 Fwww. uwgb. edu%252 Fdutchs%252 FGraphics. Geol%252 FSEISMOL%252 F 2 Kinds. Crust. gif%3 Bhttp%253 A%252 Fwww. uwgb. edu%252 Fdutchs %2 52 FEarth. SC 102 Notes%252 F 102 Orogeny. htm%3 B 400%3 B 200

Plates Movement • 10– 40 mm/year (Mid-Atlantic Ridge) to about 160 mm/year (Nazca Plate) • Plate moves as a single independent unit.

Plate Movement and the Distance between regions Source: https: //www. google. com. pk/search? q=plate+tectonics+theory&biw=1366&bih=667&tbm=isch&tbo=u&source=univ&sa=X&ei=v 40 VMKz. OIb. Cs. ASXpo. KIAw&ved=0 CDIQ 7 Ak#tbm=isch&q=tectonic+plate+showing+new+york+and+london&facrc=_&imgdii=_&imgrc=f. LFg. U 7 uily. Mx. YM%253 A%3 Bn. WRblyqp. Swbj. M%3 Bhttp%253 A%252 Facademic. brooklyn. cuny. edu%252 Fgeology%252 Fgrocha%252 Fplates%252 Fimages%252 Fmap 1. jpg%3 Bhttp%253 A%252 Fac ademic. brooklyn. cuny. edu%252 Fgeology%252 Fgrocha%252 Fplates%252 Fplatetec 21. htm%3 B 800%3 B 374

Evolution of the Earth Surface

Super-Continent Pangaea Source: https: //www. google. com. pk/search? q=plate+tectonics+theory&biw=1366&bih=667&tbm=isch&tbo=u&source=univ&sa=X&ei=v 40 VMKz. OIb. Cs. ASXpo. KIAw&ved=0 CDIQ 7 Ak#facrc=_&imgdii=_&imgrc=5 PNJPSNy. Is. Ste. M%253 A%3 B--J 1 g 7 n 11 rhf. M%3 Bhttps%253 A%252 Fwww. isgs. illinois. edu%252 Fsites%252 Fisgs%252 Ffiles%252 Fimages%252 Foutreach-images%252 Fpangea 250. gif%3 Bhttps%253 A%252 Fwww. isgs. illinois. edu%252 Foutreach%252 Fgeology-resources%252 Fplate-tectonics-mysteries-solved%3 B 320%3 B 230

Source: https: //www. google. com. pk/search? q=plate+tectonics+theory&biw=1366&bih=667&tbm=isch&tbo=u&source=univ&sa=X&ei=v 40 VMKz. OIb. Cs. ASXpo. KIAw&ved=0 CDIQ 7 Ak#facrc=_&imgdii=_&imgrc=FE 2 Om 5 B 2 J 44 s. LM%253 A%3 B 8 f 58 m. Tce. Z 0 rc. MM%3 Bhttp%253 A%252 Fskywalker. cochise. edu%252 Fwel lerr%252 Fstudents%252 Ficeage 2%252 Fproject_files%252 Fimage 012. jpg%3 Bhttp%253 A%252 Fskywalker. cochise. edu%252 Fwellerr%252 Fstudents%252 Ficeage 2%252 Fproject. htm%3 B 420%3 B 288

What drives plate tectonics? • cooling of Earth (convection) • Gravity

Plate Boundaries • The location where two plates meet. Types: • Transform boundaries • Divergent Boundaries • Convergent Boundaries

Divergent Boundaries Source: https: //www. google. com. pk/search? q=divergent+boundary&biw=1366&bih=667&tbm=isch&tbo=u&source=univ&sa=X&ei=5 J 46 VOe. ED 8 rea. JDyg. Og. H&sqi=2&ved=0 CBo. Qs. AQ#facrc=_&imgdii=_&imgrc=c 1 V 8 HP xe. Sni 4 b. M%253 A%3 BDo. LNVn 1 phl. M 57 M%3 Bhttp%253 A%252 Fwww. cotf. edu%252 Fete%252 Fimages%252 Fmodules%252 Fmsese%252 Fearthsysflr%252 FEFPlate. P 3. gif%3 Bhttp%253 A%252 Fwww. cot f. edu%252 Fete%252 Fmodules%252 Fmsese%252 Fearthsysflr%252 Fplates 3. html%3 B 294%3 B 175

Convergent Boundary Source: https: //www. google. com. pk/search? q=divergent+boundary&biw=1366&bih=667&tbm=isch&tbo=u&source=univ&sa=X&ei=5 J 46 VOe. ED 8 rea. JDyg. Og. H&sqi=2&ved=0 CBo. Qs. AQ#tbm=isch&q=converg ent+ boundary&facrc=_&imgdii=_&imgrc=32 EUGm. KSa 3 b. Dn. M%253 A%3 BSUoi. Jc. Jf. I 1 m. La. M%3 Bhttp%253 A%252 Fgeography. unt. edu%252 F~williams%252 Fgeog_3350%252 Fexamreviews%252 Fexam 1 im ages%252 FFg 16_09 b. jpg%3 Bhttp%253 A%252 Fgeography. unt. edu%252 F~williams%252 Fgeog_3350%252 Fexamreviews%252 Ftectonics. htm%3 B 600%3 B 400

Convergent Boundary • subduction zone • continental collision

Convergence Types • Oceanic-Continental • Continental-continental • Oceanic-oceanic

Pacific Ring of Fire Source: https: //www. google. com. pk/search? q=ring+of+fire&biw=1366&bih=667&source=lnms&tbm=isch&sa=X&ei=5348 VLG_Ld. Tmav. W 3 gu. AC&sqi=2&ved=0 CAYQ_AUo. AQ#facrc=_&imgdii=_&imgrc=5 o 4 b. Q C 4 r. P t. Hs. NM%253 A%3 Bs. Nd. Gd 3 KUHKOZl. M%3 Bhttp%253 A%252 Fwww. enchantedlearning. com%252 Fsubjects%252 Fvolcano%252 Fgifs%252 Fringoffirecolor. GIF%3 Bhttp%253 A%252 Fwww. encha nte dlearning. com%252 Fsubjects%252 Fvolcano%252 Fringoffire%252 F%3 B 584%3 B 434

• Eurasian plate and Indian plate collide, resulting in high mountainous range, The Himalayas. Source: https: //www. google. com. pk/search? q=divergent+boundary&biw=1366&bih=667&tbm=isch&tbo=u&source=univ&sa=X&ei=5 J 46 VOe. ED 8 rea. JDyg. Og. H&sqi=2&ved=0 CBo. Qs. AQ#tbm=is ch& q=himalayas+a+convergent+boundary&facrc=_&imgdii=_&imgrc=PXx 6 HDEEWHov. HM%253 A%3 BAy. St 6 XCS 33 IALM%3 Bhttp%253 A%252 Fquake. eas. gatech. edu%252 FExercises% 252 FPlanet. XMod 3 Act 1_files%252 Fimage 002. jpg%3 Bhttp%253 A%252 Fquake. eas. gatech. edu%252 FExercises%252 FPlanet. XMod 3 Act 1. htm%3 B 251%3 B 291

Mariana Trench Source: http: //en. wikipedia. org/wiki/Mariana_Trench#mediaviewer/File: Cross_section_of_mariana_trench. svg

Sea Floor Spreading

Mapping the Mid-Ocean Ridge • The mid-ocean ridge is the longest chain of mountains in the world. • In the 1950’s scientist mapped the mid-ocean ridge using sonar. • Sonar is an instrument that uses sound waves to measure distance. • It bounces sound waves off underwater objects and records the echoes of these sounds.

• The time that it takes the echo indicates the distance to the object. • The scientists found out that the ocean floor was not flat. • This discovery peaked their curiosity to discover what the ridge was and how it got there.

There are huge mountain ranges called ridges. Mid-Atlantic Ridge

Evidence for Sea-Floor Spreading • In 1960, Harry Hess studied Wegener’s theory. • Hess proposed the radical idea that the ocean floors move like a conveyer belt, which in turn move the continents. • This movement begins at the mid-ocean ridge, which forms along in a crack in the oceanic crust. • At the mid-ocean ridge, molten materials rise from the mantle and erupts. • The molten material spreads out, pushing older rock to both sides of the ridge.

• Hess called this process Sea-Floor Spreading. • Molten material, magnetic stripes and drilling samples supported Hess’s theory.

Evidence from Molten Material • In the ’ 60’s, scientist used a small submarine called Alvin to explore the ocean floor. • Alvin’s crew found rocks shaped like pillows or toothpaste squeezed from a tube. • These rocks showed that molten material had erupted many different times from cracks along the mid-ocean ridge.

Evidence from Magnetic Stripes • The Earth is like a giant magnet with a north and south pole. • The Earth’s magnetic poles reversed themselves 780, 000 years ago. • Rocks on the ocean floor are in a pattern of magnetized stripes. • These stripes show when the Earth reversed it’s magnetic field.

More Evidence from Magnetic Stripes • Molten material contains iron. • As it cooled, the iron bits lined up in the direction of Earth’s magnetic poles. • When the rock hardened, the iron was locked in place, giving the rocks a permanent “magnetic memory”.

More Evidence from Magnetic Stripes • Scientist recorded this “magnetic memory” on both sides of the mid-ocean ridge. • They found a stripe of when the magnetic field pointed north and a parallel stripe that pointed south. • Rock that hardens at the same time would have the same magnetic memory.

Evidence from Drilling Samples • The Glomar Challenger is a drilling ship that recovered drilling samples from the ocean floor. • They studied the age of the rocks sampled. • They found that the farther from the ridge, the older the rock. • The youngest rocks were at the center of the ridge.

Subduction at Deep-Ocean Trenches • The ocean floor plunges into deep underwater canyons called deep-ocean trenches. • Subduction takes place where there are deepocean trenches. • New oceanic crust is hot. • It moves away from the mid-ocean ridge and cools, making it more dense.

• Gravity pulls the denser, older crust down beneath the trench. • Subduction allows the ocean floor to mantle that takes sink back into the of years. tens of millions

Subduction and Earth’s Ocean’s • Subduction and sea-floor spreading change the size and shape of the oceans. • The ocean floor is renewed every 200 million years.

Subduction in the Pacific Ocean • The Pacific Ocean covers 1/3 of the planet, but it is shrinking. • There is a ring of trenches that surrounds the Pacific Ocean. • This occurs because a deep ocean trench swallows more oceanic crust than the mid-ocean ridge can produce. • If new crust is not added fast enough, the width of the ocean shrinks.

Subduction in the Atlantic Ocean • The Atlantic Ocean is expanding. • The Atlantic Ocean has only a few trenches. • The Atlantic Ocean floor is attached to the continental crust of the continents. • As the sea-floor spreads, the continents along that edge also move.