PSY320H1 Lecture Notes - Lecture 2: Metamorphic Rock, Volcanic Arc, Lithification
Lecture 2
Chemistry
• Mass number = protons + neutrons
• Isotopes of an element behave differently
• Some isotopes are radioactive and decay until they become non-radioactive stable isotopes (converted to a different
element)
• Early geologist was able to determine relative age (which came before) but could not determine absolute age this is only
available
Age of the Earth
• Archbishop Ussher of Ireland gives an age of about 5600 years
• Darwin said 300,000,000 years based on how long it would have taken large
valleys to erode
•
• William Thompson said 100,000,000 years based on temperatures
• Claire Patterson said 4.55 Ga old from radioactivity
o Now we have absolute time
Geology
• Lithosphere: crust + upper mantle
• Athenosphere: warmer ductile layer of the mantle that "flows"
o Upper mantle
• Mantle: surrounds the core, thick layer of rock
• Core: the planet center, consisting of Fe (solid inner core and molten outer
core
Plate Tectonics
• Movement of lithospheric
plates
• There are 15 major tectonic
plates
• Where two plates meet 3
things occur;
1. Intense geological
activity
2. Earthquakes/volcanoes
3. Mid-ocean ridges
• There are 2 types of crust;
1. Continental crust which is less dense, thicker, and older
2. Oceanic crust which is dense, thin, young
o Movement of plate tectonic is driven by heat energy from the mantle and core
derived from radioactive decay
o Just as there are 2 types of crust where plate tectonics meet there are 3 types of
plate boundaries;
1. Divergent: these are also called spreading plate boundaries because these
occur where newly formed oceanic crusts move away from the ridge axis so
more magma rises and more crust form
1. Gives rise to mid-ocean ridge
2.
3. Associated with head flow (reflects rising of magma)
2. Convergent: these are regions where oceanic crust returns to the mantle which
are called subduction zones
1. Surface expression of a subduction zone is a trench and a volcanic
arc
a. Convergent of two oceanic plates → volcanic island arc
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