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Lecture'7'Triple'Junctions'• Places'where'3'plate'boundaries'coincide'• Triple'junctions'migrate'and'change'across'time'Hot'spots''• Volcanic'plumes'independent'of'tectonic'plates'• Mafic'magmas'derived'from'the'lower'mantle''• Tattoo'overriding'plates'with'volcanoes'• Volcanoes'perforate'overriding'plates''• Make'volcanoes'that'drift'offAplume'• Volcano'goes'extinct'and'erodes'• Subsidence'creates'a'seamount/'guyot'• Supports'seafloor'spreading'• Seamounts/islands'age'away'from'originating'hot'spot'• Age'change'marks'direction'of'overriding'plate'motion''Tectonic'boundaries'evolve'Oceanic'plates'• Created'at'MOR'spreading'centers'• Destroyed'at'subduction'zones'Continental'plates'• Torn'apart'at'rifts'• Joined'during'collision'Continental'Rifting'• Continental'lithosphere'can'break'ap art'• Lithosphere'stretches'and'thins'• Brittle'upper'crust'faults'• Ductile'lower'part'flows'• Asthenosphere'melts'• Melts'erupt'leading'to…'• Sea'floor'spreading'• ExampleA'East'Africa'Rift'Plate'Collision'Subduction'consumes'ocean'basins'Ocean'closure'ends'in'continental'collision''Buoyant'continental'crust'will'not'subduct'Subduction'ends;'mountains'are'smashed'upward'Plate'tectonic'collision'may'involve…'• Two'continents'• A'continent'and'an'island'arc'Collision'“sutures”'the'convergent'plat e'boundary'Driving'Mechanisms'Old:'plates'are'dragged'atop'a'convecting'mantle'(convection)'Modern'• RidgeApush'–elevated'MOR'pushes'adjacent'lithosphere'• SlabApull'–gravity'pulls'a'subducting'plate'downward'• Convection'in'the'asthenosphere'adds'or'subtract s'Plate'Velocities'Absolute'plate'velocities'may'be'mapped'by…'• Plotting'plate'motion'relative'to'a'fixed'spot'in'the'mantle''• Measuring'volcano'ages/'distance'along'a'hot'spot'track'• Plate'vectors'are'determined'by'GPS'measurements'• Knowledge'of'plate'motion'is'now'accurate'and'precise'The'Dynamic'Planet'Plate'Tectonics:'the'key'to'understanding'geology'• Mantle'is'transferred'to'the'surface'and'back'down'again'• The'interior'and'surface'of'Earth'are'in'constant'motion'• Explains'earthquakes,'volcanoes,'and'continental'drift'• Earth’s'surface'changes'continuously'• Earth'looked'different'in'the'past''•


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FSU GLY 1000 - Lecture 7

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