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Plates Guest Lecture by Dr. Webster Vocabulary of the Day • • • • • • Asthenosphere Continental crust Convergent margin Divergent margin Earthquake Lithosphere • Oceanic crust • Plate tectonics Subduction • Transform margin • Volcano • Volcanoes Goals • Distinguish among types of plate tectonic settings produced by plates diverging, converging, and sliding past each other. • Relate modern and ancient geologic features to each kind of plate tectonic setting. • Relate certain geologic hazards to specific plate tectonic settings. • Universal principles are discovered through observation and experimental verification. Prior Knowlege • Please get out a piece of paper and write your name on it. • What do you already know? I’m going to show you a few geographic features, I would like you to tell me • A) What is it (name if you know)? • B) How it was formed? Question 1 • A) What is it? (name if you know) • B) How did it form? Question 2 • A) What is it? (name if you know) • B) How did it form? Question 3 • A) What is it? (name if you know) • B) How did it form? Question 4 • A) What is it? (name if you know) • B) How did it form? Question 5 • A) What is it? (name if you know) • B) How did it form? Question 6 • What ONE idea or concept do all five of those geographic features have in common? Plate Tectonics history • Plate Tectonics is relatively modern model to explain many disparate observations - like the 5 slides from the beginning. • Observations supporting a ‘drift’ theory were made as far back as 1600s • Taylor and Wegener in early 1900s published more complete drift theory Drift • Observations supporting drift – Fossils – Shapes of continents • BUT - in early 1900’s lacked any way to explain drift • What could make rock cross rock? Post WWII • • • • Paleomagnetism Seafloor spreading + Drift evidence Observations all need to be explained by a coherent model • Plate Tectonics! • This was a major shift in the scientific view of how the world works Model of Earth Today • Draw • Three things can happen at the boundaries Today - convergent • • • • • • Two types of crust Drawing So - can have 3 combos of convergent Oceanic crust-oceanic crust Continental crust-continental crust Continental crust-oceanic crust Two Types of Crust • Oceanic – Thinner (7 km) – Different material (basalt) – More dense (3 g/cm^3) – Younger (200 million years old) • Continental – Thicker (10-70 km) – Volcanic rock with sedimentary on top – Granitic materials – Less dense (2.7 g/cm^3) – Older - billions of years Model of plate tectonics • Must explain the appearance of landscape features - observations Continental-Oceanic • • • • Predict - which will go under? What prior knowledge use to predict? Draw Subduction Melting Temperatures Material Melting point (degrees C) 100 Water Quartz, K-feldspar, Naplagioclase, micas. Amphibole, Ca/Naplagioclase 600 Olivine, pyroxene, Ca-rich plagioclase 1000 800 http://hyperphysics.phy-astr.gsu.edu/HBASE/geophys/meltrock.html Subduction predictions • Make a list • Where do we expect to see continental oceanic crust collisions SA • http://geol ogy.com/ platetectonics. shtml You try • Oceanic crust - oceanic crust • Label features you expect to see. Examples on Earth • http://geology.com/plate-tectonics.shtml • Top down drawing of area • Can you identify any other places on Earth? Aleutians Continental-Continental • Where on the map? Himalayas • Folded sedimentary rock – Sedimentary suggests ocean bed – Folding pattern suggests bottom to top pressure http://library.thinkquest.org/10131/geology_visual.html Hazards associated with convergent margins • Volcanoes • Earthquakes Summary so far • The plate tectonic model describes how plates can collide. • Colliding plates explain volcanoes, earthquakes, oceanic trenches, island arcs, mountains, and the relative positioning of these features. • One model - describes many observables. Plate Tectonics Model • Hypotheses often cause scientists to develop new experiments that produce additional data. • Think of an experiment that might support plate tectonics model More support for plate tectonics • And also directly measured motions with VLBI in 1980’s! • And ground based positions with satellites in 1990’s Assessment • Write a paragraph describing how the Aleutian Islands and nearby geographical features formed. Sketch the relevant plate configuration with features.
