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Ocean-Ocean Convergent Boundary Two oceanic plates move toward one another Trench and island arc One plate moves down = subduction 03.05.a1 Features and Processes in Ocean-Ocean Convergence Trench Eruptions form volcanic island arc Accretionary prism Slab releases water Water causes melting of mantle Sketch ocean-ocean convergence, labeling the processes in your own words 03.05.a1 Ocean-Continent Convergent Boundary Oceanic and continental plate converge Volcanoes and squeezing form mountain belt Trench Oceanic plate subducted beneath continent Overlying mantle melted Sketch ocean-continent convergence, labeling the processes in your own words 03.05.b1 Observe the distribution of volcanoes around the Pacific Ring of Fire What do you think could explain the overall pattern? 03.05.c1 Pacific Ring of Fire Oceanic plates subducted on both sides Spreading in East Pacific Rise Subduction beneath oceanic plates = island arcs (e.g., Japan) Subduction beneath continental plates = mountain belts with volcanoes (e.g., Andes) Explain the Pacific Ring of Fire, including why the west and east sides are different 03.05.c2 Continent-Continent Convergence Two continents collide Subduction of oceanic part of plate Subduction brings continents closer Continents collide 03.05.d Continental collision = wide zone of deformation Pieces sliced off Thick crust = high elevation Few volcanoes Continental plate buoyant, so subduction ends Sketch a continental collision, labeling the processes in your own words 03.05.d3 Transform Boundary Observe how these two “plates” are moving past each other Transforms link spreading segments in mid-ocean ridges Plates move horizontally past one another on transform boundaries Transforms link other types of plate boundaries 03.06.a1 Observe the pattern of the Mid-Atlantic Ridge Spreading segments Transforms link spreading segments 03.06.a2 Sketch a transform boundary, labeling the processes in your own words Observe plate boundaries near the west coast of North America (green lines are transform boundaries) 03.06.b1 What Moves the Plates? Ridge push Slab pull Other forces, such as convection in mantle 03.07.a1 Rates of Relative Plate Movement Plates move cm/year Some move faster than others 03.07.b1 Which plate boundaries have the fastest rates? Geometry of Plate Boundaries Observe how the motion of these two plates varies as the boundary changes orientation Spreading along this orientation As boundary changes orientation, plates move horizontally past one another Transform boundaries link other types of plate boundaries, like two spreading centers or a spreading center with a subduction zone 03.07.d1 Geometry of Plate Boundaries II Observe how the motion between the North American and Pacific plates varies as the boundary changes orientation As boundary bends, becomes convergent (Pacific plate subducted beneath NA) Transform boundary here (Queen Charlotte fault), with plates moving horizontally past one another 03.07.d1 Test of Plate Tectonics Is Age of Seafloor and Thickness of Sediment Drill cores Volcanic rocks in crust youngest near ridge (just formed) Sediment Volcanic rocks Sediment thickens away from ridge (had more time to accumulate) 03.08.a1 Formation of Linear Island and Seamount Chains Lines of islands and seamounts (e.g., Hawaii) Plate moves over a hot spot Plate subsides as cools, so islands become seamounts Volcano forms over a hot spot Volcanoes become inactive as area moves away from hot spot 03.08.c Why is South America Lopsided Observe the features around South America Envision a cross section from west of South America to the MidAtlantic Ridge 03.09.a1 Compare this cross section with the one you envisioned Andes (mountains and volcanoes) over subduction zone, with trench offshore Subduction beneath western edge Spreading along mid-ocean ridge Eastern edge of continent not a plate boundary (passive margin) 03.09.b1 Middle Mesozoic (140 m.y ago) Late Mesozoic (100 m.y ago) Evolution of South America Observe the evolution of South America, beginning with continental rifting away from South America Present 03.09.c Investigation: Where is the Safest Place to Live Continent A Continent B Identify possible plate boundaries in this area and indicate whether the boundary is divergent, convergent, or transform Identify where you would get earthquakes and volcanoes, and then determine where it is safest to live 03.10.a1 Sketch the geometry of the plates in the subsurface, using figures in the textbook as a guide to the geometries of the plates and thickness of the lithosphere, oceanic crust, and continental crust 03.10.a