Plate Tectonics Charity I. Mulig

Tectonics – Refers to the deformation of the Earth’s crust – results in the formation of structural features such as mountains

Continental Drift Hypothesis Proposed by Alfred Wegener stated that the continents had once been joined to form a single supercontinent which started to break up 200MYA ago forming the present land masses

ne.com/books/eart h_science/terc/cont ent/visualizations/e s0806/es0806page0 1.cfm?chapter_no= 08 ne.com/books/eart h_science/terc/cont ent/visualizations/e s0806/es0806page0 1.cfm?chapter_no= 08 Wegener – continental Drift Wegener – continental Drift Bullard – Continental Drift Bullard – Continental Drift

Evidences

1. The Jigsaw Puzzle Landmasses appear to be connected If landmasses are joined together at the continental shelves, a better fit is made

2. Fossils Match Across the Seas Fossil evidence for continental drift includes several fossil organisms found on different landmasses.

3. Rock Type and Structure Match

4. Ancient Cimates

Rejecting the Hypothesis Wegener couldn’t accunt for a driving mechanism His proposal was that tides caused the plates to move. His proposal was immediately countered by the fact that such tides of such magnitude could stop the earth’s rotation in a few days

Plate Tectonics Theory A more encompassing theory than the continental drift theory States that – The earth is composed of plates that float above the mantle – These plates interact along their boundaries

Types of Tectonic Plates Continental Plates Less dense than oceanic plates Floats higher in the mantle than the oceanic plates Composed of silica-rich rocks Found in the continents Oceanic Plates Denser than continental plates Darker and floats deeper in the mantle Composed of basalt and gabro Is younger when found closer to oceanic ridges

Types of Plate Boundaries Convergent Plate Boundaries May form the following features: Mountain belts (CP vs CP) Island arcs (OP vs CP) Volcanic arcs (OP vs OP) Divegent Plate Bundaries (spreading centers) May form the folowing features Oceanic ridges Rift valleys Formation of oceans Transform-Fault Plate Bundaries Results to earthquakes

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Evidences

1. Paleomagnetism Molten rocks can provide records of ancient magnetic fields. There is evidence from these ancient rocks that there seems to be – Polar wandering – Magnetic reversals and seafloor spreading

2. Earthquake Patterns Earthquakes frequently occur along plate boundaries The depth of earthquakes supports can be used as an evidence of the subduction phenomena

3. Ocean Drilling Ocean drilling provides evidences that age of rocks increases with distance from midoceanic ridges.

4. Hot Spots A hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface; The Pacific plate moves over a hot spot, producing the Hawaiian Islands. Hot spot evidence supports that the plates move over the Earth’s surface.

Causes of Plate Motion Convective Flow – major driving mechanism Slab-pull Ridge-Push Mantle Covection – Mantle plumes

Mantle Convection Models zations/es0805/es0805page01.cfm?chapter_no=08

Additional Links physics/visualizations/PTMovements.html physics/visualizations/PTMovements.html e/photos/plate-tectonics-gallery/#/rift- escarpments-eritrea_1169_600x450.jpg e/photos/plate-tectonics-gallery/#/rift- escarpments-eritrea_1169_600x450.jpg e/earth/the-dynamic-earth/plate-tectonics- article.html e/earth/the-dynamic-earth/plate-tectonics- article.html