2In order to study Plate Tectonics, we must first reorganize our layering system for the Earth: Old System – 4 layersCrust (rigid)(rigid)Mantle (putty like)(semi rigid)Outer core (liquid)Inner core (solid)New System – 5 layersLithosphereAsthenosphereMantleOuter CoreInner Core
6What is Plate Tectonics? Earth’s surface is made up of moving, solid pieces called plates(Reference Tables pg 5)Plate tectonics is the study of the formation and movement of these platesEarth’s plates are part of the lithosphereThe lithosphere is the crust and the upper part of the mantle
8Properties of the Crust Oceanic crust is mainly made of the igneous rock basaltContinental crust is mainly made of the igneous rock graniteOceanic crust is denser than continental crust (b/c basalt is MAFIC…remember?...ROCKS!)
10How Plates Move… Asthenosphere - middle part of the mantle Similar composition to the rigid upper mantle, but it is partially meltedThis makes the asthenosphere like a very thick “liquid” (viscous)(think VERY THICK MUD or SILLY PUTTY)The “liquid” property of the asthenosphere allows it to flow very slowly
12How Plates Move…cont’d You can think of the lithospheric plates as “floating” on the asthenosphereThe heat from inside the Earth causes convection currents to form in the asthenosphereWhere convection currents rise, molten rock forces the plates apartWhere the convection currents are sinking, the plates are moving together
14DIVERGENT BOUNDARY CONVERGENT BOUNDARY MOUNTAIN BUIDLING NEW ROCK LIQUID HOT MAGMALIQUID HOT MAGMA
15Alfred Wegener’s Theory of Continental Drift In 1915, German geologist and meteorologist, Alfred Wegener, first proposed the theory of continental drift, which states that parts of the Earth's crust slowly drift atop a liquid coreWegener hypothesized that there was a gigantic supercontinent 200 MYA, which he named Pangaea, meaning "All-earth“Wegener published this theory in his book, On the Origin of Continents & OceansWegener
19OK, so we’re saying that the lithospheric plates move around on top of the asthenosphere, but what evidence do we have of this Plate Movement?
20Evidence of Plate Movement 1) “Puzzle-like” fitThe shape of the west coast of Africa and the east coast of South America seem to fit together like a puzzleIt is believed that they were once together, but moved apart over time (Theory of Continental Drift)
22Evidence of Plate Movement 2) Geologic EvidenceSimilar fossil remains in Africa and South America of a reptile that is found nowhere else in the worldDistinctive rocks were also found in Africa and South America in regions where the two continents were most likely joined together
26Evidence of Plate Movement 3) The majority of earthquakes and volcanoes are found in belts that occur along plate boundaries (where the plates are moving together or apart)Ex. the Pacific Ring of Fire
28Evidence of Plate Movement 4) Magnetic polarity reversals are recorded in ocean floor rocks as the sea floor spreads apartDuring certain periods in Earth’s history, the magnetic fields have reversedIron in the igneous rocks on the ocean floor would shift before the magma cooled and hardenedIf the polarity changed, new magma would cool with minerals shifted in the opposite direction
31Evidence of Plate Movement 5) Heat flowing out of the rocks (temperature) is greatest where the rocks are spreading apart (rising convection current)Heat (temperature) decreases where the rocks are moving together(sinking convection current)
343 Main Types of Plate Boundaries I Divergent BoundariesII Transform BoundariesIII Convergent BoundariesA. Collision (C-C)B. Subduction (O-C) & (O-O)
35Plate BoundariesDivergent Boundaries- plates are moving apart at spreading centersThese boundaries form mid-ocean ridges or rises (like underwater mountain ranges)In between the 2 peaks of the ridge are valleys called rift valleysEx. mid-Atlantic Ridge, East Pacific Ridge
39Plate BoundariesTransform (Sliding) Boundary - 2 plates slide past each otherThe sliding movement often causes earthquakes to occur along faultsA fault is nothing more than a crack in the Earth’s crust where movement has occurredEx. North American Plate and the Pacific Plate are sliding past each other along the San Andreas Fault in California
43Convergent Boundaries - two plates are converging or coming together (2 main types)
44Type 1 Collision Boundary (continental-continental) (C – C) - the two plates moving together are both continental crust platesThe collision causes the plates to form a single, larger continent and the crust is pushed upward into a mountain rangeEx. Himalayan Mountains (including Mt. Everest). The Indian Plate and the Eurasian Plate are still moving together, so Mt. Everest is still slowly getting taller!
47Type 2Subduction Boundary - one of the plates plunges under (subducts) the otherOccurs between two oceanic plates (O-O), or an oceanic and continental (O-C) plateMost common characteristic is adeep-sea trench VIF!!!!These trenches are the deepest spots in the oceanEx - the Marianas Trench is approx. 35,000 feet deep! Mt. Everest could be put into the trench and the peak would still be about 1 mile below the ocean’s surface!
51Subduction Boundaries cont’d Because oceanic crust is denser than continental crust, the oceanic crust will always subduct underneath the continentalVolcanoes always seem to form at subduction boundariesIf two oceanic plates converge, volcanic islands will form (ex - Aleutian Islands in Alaska)If one plate is continental and the other oceanic, the volcanoes will form along the edge of the continental crust (ex - Cascade Mountain Range on Western US)
52Subduction Boundaries cont’d When the oceanic crust gets buried deeper and deeper under the Earth, it begins to melt into “liquid hot” magma.Since “liquid hot” magma is less dense than the solid rock surrounding it, it has to rise.When it rises, it comes to the surface of the Earth and forms volcanoes.