ESS105H1 Lecture 2: Tectonic Plates I

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Published on 31 Jan 2019
Lecture 2: Plate Tectonics
Some lines of earthquakes coincide with mid-ocean
ridges while other coincide with deep ocean trenches
Earthquakes, volcanism, or mountain building
(elevation) = tectonic activity
Belts of tectonic activity divide lithosphere into tectonic
Earthquakes, volcanoes, and mountain belts are not
randomly distributed; they are conc. In certain areas -
therefore 2 hypotheses:
1. Areas with few earthquakes are rigid plates, and
the lines along which earthquakes most commonly
occur represent the boundaries (or edges) of those
rigid plates
2. earthquakes occur along the edges of the rigid
plates because each plate is moving in a different direction
Plate Tectonics
Plate tectonics is the unifying theory in geology that explains how the movement of tectonic plates are
related to geological features
o A single tectonic plate may include all or part of a continent and part of an ocean basin
A plate boundary is simply the boundary zone between two plates: the edge of a plate, where it is in
contact with another plate
o Earthquakes occur along plate boundaries where two plates move relative to each other
Plate Boundaries: Divergent
There are three types of plate boundaries (each has a specific symbol
for maps): Divergent, convergent, and transform
o Mid-ocean ridges are found at divergent plate boundaries
Oceanic-divergent boundaries are when oceanic plates move apart
in the ocean (i.e. Seafloor spreading) and new oceanic crust is formed
o Processes: hot mantle below rises up the crust, forming a
mountain chain and creating high heat flow
o Earthquakes that occur at divergent boundaries are small
because the lithosphere is thin
o Black smokers: hot springs that carries dissolved metals is
common along mid-ocean ridges - crabs, tube worms,
thermophilic bacteria
Continental divergent boundaries: initial uplift from rising mantle
causes stretching and faulting which form a rift and melting
forms magma this can lead to seafloor spreading and new
ocean basin
Oceanic crust is created at spreading centres (i.e. divergent
plate boundaries) and destroyed at subduction zones (i.e.
Convergent plate boundaries)
Plate Boundaries: Convergent
Convergent plate boundaries are when two plates collide
with each other
o If one of the plates is carrying oceanic crust, it may
sink back down into the mantle along a subduction
o A deep, oceanic trench forms where a plate bends to
go down a subduction zone
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