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 MaterialMelting point (degrees C) Water100 Quartz, K-feldspar, Na- plagioclase, micas. 600 Amphibole, Ca/Na- plagioclase 800 Olivine, pyroxene, Ca-rich plagioclase

Subduction predictions Make a list Where do we expect to see continental - oceanic crust collisions

SA ogy.com/ plate- tectonics. shtmlhttp://geol ogy.com/ plate- tectonics. shtml

You try Oceanic crust - oceanic crust Label features you expect to see.

Examples on Earth 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

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.