1)The plate tectonic system 2)A theory is born 3)Early evidence for continental drift 4)Continental drift and paleomagnetism 5)Plate boundaries 6)History and future of plate motions 7)Mantle convection system Plate Tectonics (Part II) Plate boundaries define the major lithospheric plates. Blue: Seafloor spreading; Green: Transform faulting; Red: Subduction Plate boundaries 5) Plate boundaries PLATETECTONICS Plate boundaries Earthquake occurrence coincides with plate boundaries, reflecting the energy released during subduction, seafloor spreading or plates sliding past each other (transform). See Fig ) Plate boundaries PLATETECTONICS Divergent (constructive) Transform (shear) New material is added to the plates at spreading center Lithospheric plates are destroyed when they converge at trenches. Plates slide past each other. Plate boundaries 5) Plate boundaries PLATETECTONICS Divergent (constructive) Convergent (destructive) 2.5 5) Plate boundaries PLATETECTONICS Transform (shear) 2.10 M id-ocean ridges form a continuous mountain chain winding around the globe through all ocean basins. They resemble the seams of a baseball. Divergent plate boundaries Divergent plate boundaries 5) Plate boundaries PLATETECTONICS PLATETECTONICS Oceanic type Continental type Divergent plate boundaries Divergent plate boundaries 5) Plate boundaries PLATETECTONICS Rifts opening by the divergence of the Arabian plate from the African Plate formed the Gulf of Suez and Gulf of Aqaba. Rift opening by the divergence of Baja California from the Mexican mainland creates the Gulf of California. 5) Plate boundaries PLATETECTONICS The mid-Atlantic ridge surfaces in Iceland. New volcanic material fills the rift valley as plates are pulled apart. ocean-ocean ocean-continent continent-continent 5) Plate boundaries PLATETECTONICS l Convergent boundaries Continental arc trench system Andes mountains (Peru-Chile trench), Cascade mountains (Juan de Fuca plate subduction) Island arc trench system Japan (Japan trench) Mariana (Mariana's trench) Himalayas, Alps, Appalachians Convergent boundaries Example of ocean-continent convergent boundary is the subduction of the Juan de Fuca plate off Washington unter the North-American Plate Trench Eruption of Mount St. Helens ) Plate boundaries PLATETECTONICS 4. Growth of ocean basins The breakup of Pangaea : A) Upwarping, stretching Molten basalt moves through the cracks of the lithosphere B) Formation of a rift valley. Two continents are separated by a valley that downdrops and eventually floods C. Linear sea. The high density basalt sinks below sea level, a new ocean basin forms. D. After millions of years, the rift becomes the new mid-ocean ridge. Continental margins form. 5) Plate boundaries PLATETECTONICS 6) History and future of plate motionsPLATETECTONICS 750 Ma Late Proterozoic supercontinent Rodinia 458 Ma Middle Ordovician Gondwana forms 390 Ma Early Devonian Euramerica forms 237 Ma Early Triassic supercontinent Pangaea 195 Ma Early Jurassic Breakup of Pangaea 152 Ma Late Cretaceous N and S Atlantic opened Future plate motions PLATETECTONICS 7) Mantle convection There are likely two convection cells in the mantle, separated by a boundary at about 700 km depth, a whole mantle convection and a shallow convection. PLATETECTONICS 7) Mantle convection One support of deep mantle convection are plumes Hotspots of lava that might originate at the core-mantle boundary and that give rise to island chains such as Hawaii. PLATETECTONICSPLATETECTONICS Distribution of Hot Spots PLATETECTONICS 7) Mantle convection Summary: Modern supporting evidencePLATETECTONICS Geomagnetism Earthquakes Deep Sea Ocean Drilling Hot spots Modern measurements Deep earthquakes line up along plate boundaries Confirmed ocean floor age increases away from mid-ocean ridge Linear island chains in direction of plate motion Using satellites to measure current movement of continents (Fig. 2.13) Earths magnetic field reversals are recorded parallel to mid-ocean ridges