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Continental Drift Alfred Wegener (1912) First serious proponent First serious proponent Alfred manning the weather station, Greenland - 1913.

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Presentation on theme: "Continental Drift Alfred Wegener (1912) First serious proponent First serious proponent Alfred manning the weather station, Greenland - 1913."— Presentation transcript:

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2 Continental Drift Alfred Wegener (1912) First serious proponent First serious proponent Alfred manning the weather station, Greenland

3 Fit of the Continents A more modern view than Wegener’s uses 1000 or 2000 m isobath as estimate of edge of continental crust

4 Fit of Structural Elements

5 Pennsylvanian (300 Ma) Glaciation Glacial striations in bedrock, South Australia

6 Pennsylvanian (300 Ma) Glaciation Using present continental locations Arrows indicate ice movement directions

7 Pennsylvanian (300 Ma) Glaciation Using pre-drift continental locations Arrows indicate ice movement directions

8 Fossil Evidence Glossopteris: an ancient seed fern (200 Ma) Distribution of Glossopteris fossils

9 Fossil Evidence Mesosaurus couldn’t swim in open ocean Distribution of Mesosaurus fossils

10 Paleomagnetism The Earth as a dipole Magnetic declination and inclination

11 Paleomagnetism Magnetization of volcanic rocks and sediments

12 Paleomagnetism “Polar Wandering” curves

13 2) The Earth’s Interior

14 Miles from ridge axis Plate Tectonics: a breakthrough Brian Mason (Scripps) led a group that studied a 2-D area spanning the Mid-Atlantic Ridge in detail An explanation of the curious magnetic anomaly pattern

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16 The process at mid-ocean ridges

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18 Black Smokers

19 Seismicity Earthquakes occur due to motion along faults Dip-slip Faults Normal Fault Reverse Fault (thrust) Normal Fault Reverse Fault (thrust) View is cross-section

20 Seismicity Earthquakes occur due to motion along faults Strike-slip Faults Right-Lateral Left-Lateral Right-Lateral Left-Lateral Map View

21 Seismicity: global distribution of earthquakes

22 Earthquake foci in the vicinity of the Japan trench

23 Seismicity First motion studies Bomb

24 Seismicity First motion studies Earthquake

25 Seismicity First motion studies tell us that earthquakes: l At ridges  normal faults (extension) l At trenches  thrust faults (compression) l At fracture zones  strike-slip faults

26 Seismicity: global distribution of earthquakes

27 The Deep-Sea Drilling Program

28 Sediment ages directly on crust

29 Age of the ocean crust

30 Hot Spots

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33 The Modern Plates

34 Three types of plate boundaries

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36 Divergent boundary

37 Where on Earth is continental rifting occurring today?

38 Transform boundary Note opposite sense of motion (first motion studies) San AndreasTransform

39 Transform boundary

40 Convergent boundary Three sub-types l Ocean-Continent l Ocean-Ocean l Continent-Continent Can you name an example of each?

41 Convergent boundary l Ocean-Continent: Andes, Cascades l Ocean-Ocean: Aleutians, Japan l Continent-Continent: Himalaya, Alps

42 Convergent boundary l Trench and subduction zone l Earthquakes l Linear chain of andesitic volcanoes (granites below) l Creation of mountain ranges (also linear chains) F Andean type - continental arc F Himalayan type - collisional (a terminal type)

43 “Andean-type” orogenesis Continental crust thickens by addition of magma from the subduction zone Compression due to plate convergence

44 “Himalayan-type” orogenesis Begins as Andean-type

45 “Himalayan-type” orogenesis How do you locate the suture zone today? How can you determine the “polarity” of subduction?

46 Slivers of oceanic crust and upper mantle (ophiolites) become incorporated into the “mélange” in the accretionary wedge of deformed sediments The “suture zone” is marked by the mélange and particularly by the occurrence of ultramafic rocks composing the mantle portion of the ocean lithosphere

47 Chain of ultramafic bodies in Vermont indicating a suture zone of the Ordovician Taconic Orogeny. The ultramafics mark a closed oceanic basin between North American rocks and an accreted island arc terrane. From Chidester, (1968) in Zen et al., Studies in Appalachian Geology, Northern and Maritime. Wiley Interscience.

48 Appalachia n History Can “accrete” island arc terranes as well as continents

49 Plate Motions

50 Plate Tectonics in the Pacific Northwest

51 The Wilson Cycle

52 The Breakup of Pangea

53 The History of an Ocean Basin

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56 Igneous Processes l Decompression partial melting at divergent zones

57 Igneous Processes l Partial melts: low-T fraction is always more Si-Al-Na- K-rich and Fe-Mg-poor than source rock. l Leaves behind Mg-Fe-rich refractory residue l Decompression partial melting at divergent zones

58 Igneous Processes l Hot spots and mantle plumes l Subduction zones:  Conveyor of basalt to melt  andesite F Water lowers melting point of mantle wedge

59 Igneous Processes l Subduction zones: water lowers melting point


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