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Map of Major Tectonic Pla E U R A S I A N P L AT E C H A L E U T I A N IL EN RI N ANA C H PH I PL LIPP AT I N E E R KU TR E N T R E MA R T CE NT A TR EN CH U T H E A S T GA O TRE INDO–AUSTRALIAN P L AT E TON S NC H V D IA N R I D E L IN G JA RA PA I N D I A N R I D G E I F I C P A C PLATE BOUNDARIES Divergent margin A N T A R C T I C A N T P L A T E Convergent margin Transform fault (arrows show relative motion) Divergent Boundaries & Spreading Zones Spreading center—Fast L i t h o s p h e re Divergent boundaries occur mostly along spreading centers where the magma rises forming new crust. (Ex. East Pacific Rise, Mid Atlantic Ridge.) Spreading center—Slow Mountains & valleys O ce a n i c c r u s t M a nt l e As t h e n o s p h e re Partial melt Spreading zones (no graphic) on continents create parallel mountains and valleys as the crust pulls apart (ex: Basin & Range, U.S. and the Lithosphere Crust Mantle Asthenosphere Partial melt Great Rift Valley, Africa. ) Background map courtesty of Scott Walker (Digital Cartography Specialist, Harvard College Library); graphics and tectonic & volcca ic Plates and Select Great Earthquakes and Volcanoe E R ID G T L A N I C T A N H N C E T R Basin & Range A JUAN dE F UC A PL ATE CARIBBEAN P L AT E M I D PUERTO RICO TRENCH AM E EN RICA CH C H I L E T R NAZCA P L AT E A D G E R I C T I C R A N T A A Convergent Boundaries Lithosphere Lithosphere Oceanic crust Co nt i n e nt a l c ru s t . . . . . . .. . . O ce an Asthenosphere ic cr us . . As t h e n o s p h e re . . . . .. . t Ocean-Ocean—Ocean plate dives beneath another ocean plate; volcanic island chain forms above the zone (ex:. The Marianas) Ocean-Continent: Ocean plate dives beneath a continental plate. Volcanic mountain chain forms inland. (ex:. Cascade Range, Sumatra, Japan) onic & volccanic features by Jenda Johnson (Volcano Video & Graphics) Co nt i n e nt a l c r u s t L i t h o s p h e re L i t h o s p h e re . As t h e n o s p h e re Co nt i n e nt a l c r u s t L i t h o s p h e re L i t h o s p h e re Asthenosphere High Pl ate a u Mo u R an t a i n ng e Vo lc an ic ar c ch en Co n t i n e n t a l crust crust Oceanic Tr ch Is la nd ar c When two plates move toward each other, crust is destroyed as one plate dives (is subducted) beneath the other. The location where sinking of a plate occurs is called a subduction zone. en A T E SCOTIA P L AT E Most of the world’s earthquakes and volcanoes are found at or near the boundary between two tectonic plates. Friction between the plates keeps them from sliding. When the frictional strain is overcome, the ground suddenly snaps along faults and fractures releasing energy as earthquakes. Volcanoes occur at divergent margins (where magma rises and erupts); at convergent margins (where an oceanic plate dives beneath another plate; magma forms in the continental plate above the diving oceanic plate), and less commonly as hot spots (where magma melts through a plate, such as Hawai`i). Tr F I C M I D P E R U REN SOUTH AMERICAN P L AT E R C H E N TR E A S T CH PA C I F I C R I S E DLE E PAC I F I C P L AT E MID I D G COCOS P L AT E O ld o ce an ic cr u st Continent-Continent: Two thick continental plates collide and buckle into high mountains. (ex: Himalaya Mountain Range.) ANT lcanoes. EURASIAN P L AT E E L A N T I R ID G HELLENIC AFRICAN P L AT E East A frican Rift S ystem AR ABI AN PL ATE E M I D I D G E A T L A N T I C R I D G AFRICAN P L AT E AM A N TA ERIC R T H S O U W E T S I N D N IA R AN RID CTIC GE SYMBOLS White arrows show plate motion direction Volcanoes (generalized) Hot spot (arrow shows direction of plate motion) g i). Great earthquakes since 1900; before 1900 Transform Boundaries rust h e re u TRENCH Crust Lithosphere Asthenosphere As surrounding plates are driven by deep forces to move apart or crunch together, the in-between areas are pushed around on the surface. This forces them to slide past each other horizontally. Spreading ridge Tra n s fo r m f a u l t Spreading ridge Lithosphere Asthenosphere Cru s t Partial melt st e Strike slip faults result from two plates moving horizontally in opposite directions (ex: San Andreas Fault, California). Transform faults are where two plates are moving away from a spreading ridge and fracture zones develop (ex: ocean floor)