CEE 1030 1st Edition Lecture 12 Basin synclinal structure youngest rocks in center Plate tectonics scientific revolution in the late 1960s unifying concept of the earth sciences gave a way of thinking to earth science Continental drift people thought maybe the continents could move horizontally recognitions of jigsaw puzzle fit of coasts on either side of atlantic Alfred Wegener 1915 Continental drift hypothesis large scale horizontal movements of continents across Earth s surface Continental drift geometric evidence computer best fit model using continental slope rather than the coast fossil evidence land dwelling reptiles and plants particularly interested in fossils more common on land paleoclimate evidence evidence for ice sheets at 300 Ma in places now in tropics Geological evidence close match of rock types and structures between the continents of look across the ocean you can see similar trends of same types of rocks many objections to Wegener s hypothesis lack of mechanism for moving continents renewed interest in 1950s initially came from rock magnetism study magnetized minerals in rocks show the direction of earth s magnetic poles determine original latitude of rock Supercontinent Pangaea Pangaea began to break up These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Paleomagnetism Polar wandering apparent calculated location of north pole different for North America Eurasia using current continent locations Pole path trajectories match when North America and Eurasia are pushed back together Seafloor spreading 1950s and 1960s saw first concerted effort to investigate the geology of the Earth s oceans Harry Hess 1962 new ocean crust at ridges but together a model that explained the mid ocean ridges Oceanic rocks are young 18 Ma Hot mantle rocks Geomagnetic reversals earth s magnetic field periodically changes polarity magnetic time scale Magnetism of seafloor rocks symmetrical linear anomalies across ridges local highs and local lows coming from the influence of magnetism of the rocks 1963 Vine Matthews Morley saying new oceanic crusts has been formed at the ridges Plate tectonics lithosphere outer rigid shell of the earth consists of uppermost mantle and overlying crust divided into a serious of rigid plates plates are in motion relative to each other and continually changing in shape and size individual plates can contain both oceanic and continental crust asthenosphere weak ductile mantle beneath lithosphere seven major plates and several smaller ones relative plate motion 1 to 15 cm year Three type of plate boundary interactions among individual plates occur along their boundaries where most of the geological action is 1 transform moving side by side 2 divergent plates moving apart from each other 3 convergent plates are moving together one plate is being destroyed Divergent plate boundary seafloor spreading at ocean ridges creation of new oceanic crust constructive plate margin continental rifting continental crust splits apart at rift Can lead to creation of new ocean Convergent plate boundary continuous creation of ocean lithosphere older parts of oceanic lithosphere denser than asthenosphere get recycled into mantle at destructive plate margins subduction zones oceanic lithosphere cools and contracts with increasing age denser than asthenosphere Subduction zone oceanic trench and magmatism oceanic oceanic convergence volcanic continental continental convergence contintenal lithosphere too buoyant to subduct Transform fault boundaries plates slide path one another No new lithosphere is created or destroyed Transform faults most join two segments of a mid ocean ridge along breaks in the oceanic crust known as fracture zones Plate tectonics predictions explains global distribution of earthquakes and volcanoes What drives plate motions Plate tectonics is response to cooling of earth Thermal convective flow in the solid mantle slab pull sinking of dense oceanic lithospheric slab Hot spots and mantle plumes active volcanoes in middle of plate Example Hawaii rising plumes of hotter mantle material stationary convincing evidence to confirm plate tectonics seafloor spreading has come from drilling into ocean floor sediments ocean crust 200 Myrs Measuring plate motions ocean floor magnetic anomalies and the magnetic time scale age of oceanic crust and spreading rate oldest ocean crust ca 200 million years Plate motion direction and speed agreement 1 GPS measurements over last decade or so Long term movement over millions of years inferred from radiometric age dating of rocks