Plate Tectonics Interactions at plate boundaries depend on the direction of relative plate motion and the type of crust Chapter 2 Which kind of plate boundary is associated with Earthquake activity A Divergent Boundary B Convergent Boundary C Transform fault Boundary D All of the above Interactions at plate boundaries depend on the direction of relative plate motion and the type of crust Interactions at plate boundaries depend on the direction of relative plate motion and the type of crust Which kind of plate boundary is associated with Earthquake activity At which kind of plate boundary is new oceanic lithosphere formed A Divergent Boundary B Convergent Boundary C Transform fault Boundary A Oceanic transform boundary B Oceanic divergent boundary C Ocean ocean convergent boundary D Ocean continent convergent boundary D All of the above Interactions at plate boundaries depend on the direction of relative plate motion and the type of crust At which kind of plate boundary is new oceanic lithosphere formed A Oceanic transform boundary B Oceanic divergent boundary C Ocean ocean convergent boundary D Ocean continent convergent boundary Plate Tectonics Learning Goals Scientific Method Development of Plate Tectonics Theory Lithosphere vs Asthenosphere Crust vs Mantle Plates contain continent and ocean Plate boundaries where the action is Convergent Boundaries Divergent Boundaries Transform Boundaries 1 Divergent Convergent and Transform plate boundaries Crust and Mantle vs Lithosphere and Asthenosphere Plates are lithosphere Both continent and ocean crust Scientific Method 1 Observation fact This is a repeatable measurement or experiment 2 Hypothesis One or more possible explanations to link observations 3 Testing Further experiment or observation to test hypothesis Non testable hypotheses also rejected 4 Theory A grand or unifying hypothesis that has survived tests Relativity Evolution Plate tectonics 1 Observation Early Evidence Wegener The geometric fit of the continents The similarity in rock age groups between adjoining regions The similarity in Paleozoic fossils The geometric fit of the continents between adjoining areas The distribution of Paleozoic glaciation in S America S Africa Australia and India 2 Similarity of Paleozoic Fossils in adjoining regions Early Objections Mantle is solid Transmits Shear waves How can continents move and remain intact What is the driving force 1960s Compelling New Evidence Magnetic Anomalies Magnetic minerals such as magnetite Fe3O4 record Earth s magnetic field They also perturb the field by a small amount Perturbations are called magnetic anomalies Anomalies can be mapped using magnetometers dragged behind aircraft or ships Magnetic Anomalies Anomalies were first solid evidence of sea floor spreading Here was a credible hypothesis that demanded testing 2 The Hypothesis The continents have moved drifted over geologic time so that North and South America have separated from Europe and Africa 3 3 Test the Hypothesis The hypothesis makes several predictions that allow it to be tested by further observation Rocks in adjoining parts of Africa and South America should be similar in age and type Rocks on Atlantic floor should get younger toward the mid ocean ridge New bathymetric measurements define the continental crust boundary Do South America and Africa still fit together If crust is being created at mid ocean ridges it should also be consumed Where is the crust consumed There needs to be a driving force 3 Test the Hypothesis Rocks in adjoining parts of Africa and South America were age dated using new radioisotopic methods they matched perfectly Rocks were dredged from the sea floor they showed ages symmetrically increasing away from the ridge There were no old rocks 250MY The fit of continents was revised using the edge of the continental slope rather than the coastline the match was nearly perfect 3 Test the Hypothesis Rocks were dredged from the sea floor They showed ages symmetrically increasing away from the ridge There were no old rocks 250MY 4 Theory of Plate Tectonics Continental Margins Passive and Active There appear to be 13 major plates that cover the globe The plates can contain oceanic or continental crust or both New oceanic crust is created at the mid ocean ridge divergent boundary Old oceanic crust is consumed subducted at convergent plate boundaries 4 Divergent Convergent and Transform plate boundaries Transform Divergent and Convergent plate boundaries Crust and Mantle vs Lithosphere and Asthenosphere Crust and Mantle vs Lithosphere and Asthenosphere Interactions at plate boundaries depend on the direction of relative plate motion and the type of crust Divergent Boundaries Oceanic Plate Separation MidAtlantic Ridge Key Figure 2 6 pages 26 27 Go to next slide to begin 5 Divergent Boundaries Divergent Boundaries Oceanic Plate Separation Continental Plate Separation Volcanoes and earthquakes concentrate MidAtlantic Ridge East African Rift Valley Divergent Boundaries Divergent Boundaries Continental Plate Separation Parallel valleys volcanoes and earthquakes East African Rift Valley Mid Atlantic Ridge East Pacific Rise Red Sea East Africa rift 6 Divergent Convergent and Transform plate boundaries Convergent Boundaries Convergent Boundaries Ocean Ocean Convergence Ocean Ocean Convergence Deep sea trench volcanic island arc Mariana Islands Marianas Trench Convergent Boundaries Mariana Islands Marianas Trench Convergent Boundaries Ocean Continent Convergence Ocean Continent Convergence Andes Mountains Peru Chile Trench A volcanic belt of mountains forms Andes Mountains Peru Chile Trench South American Plate South American Plate 7 Convergent Boundaries Convergent Boundaries Continent Continent Convergence Continent Continent Convergence Crust crumbles creating high mountains and a wide plateau No Volcanoes Himalaya Tibetan Plateau Tibetan Plateau Himalaya Main thrust fault Eurasian Plate Convergent Boundaries Ocean Ocean Main thrust fault Eurasian Plate Divergent Convergent and Transform plate boundaries Tonga trench Marianas Trench Ocean Continent West coast South America Japan Trench Aleutians Continent Continent Himalayas Alps Transform Fault Boundaries Mid Ocean Ridge Transform Fault Transform Fault Boundaries Mid Ocean Ridge Transform Fault Spreading centers offset 8 Transform Fault Boundaries Continental Transform Fault Transform Fault Boundaries Continental Transform Fault Offset continental crust The San Andreas fault The San
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