Post on 19-Jan-2016
transcript
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)
Water 100
Quartz, K-feldspar, Na-plagioclase, micas.
600
Amphibole, Ca/Na- plagioclase
800
Olivine, pyroxene, Ca-rich plagioclase
1000
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://geology.com/plate-tectonics.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.