CAS ES 107 Chapter Notes - Chapter 7: Asthenosphere, San Andreas Fault, Outer Core
7 Jun 2018
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Chapter 7: Part 3
Plates and Plate Boundaries
-the lithosphere is divided into 20 rigid plates
-tectonic activity is concentrated at plate boundaries, there’s little activity within a plate
-plates move relative to each other and a few centimeters per year
-because of friction between the plates, there’s alternating periods of stasis (stresses build) and
movement (when they are released)
-after a period of stasis, pent-up energy is released suddenly as the plates jump past each other
causing earthquakes
3 types of Plate Boundaries
Divergent→ plates move away from each other
-stresses are pulling apart the lithosphere
-these are where mid-ocean ridges form
-when the continents are being pulled apart, faulting occurs and flat-bottomed valleys
called rifts form
-divergence of the African and Arabian plates has created a system of rifts that radiate
from a central point called a triple junction
Convergent→ plates move towards each other
-we’ve determined that earth is not increasing in size, so we revealed that seafloor is
consumed at deep-sea trenches about as fast as it is being produced at mid-ocean ridges
-deep sea trenches form when two oceanic plates collide and one oceanic with one
continental
***however continental + continental form mountains
Oceanic-Continental + Oceanic-Oceanic
-when two oceanic plates collide, the leading edge of one plate sinks beneath the other
-when its oceanic-continental, the denser oceanic crust sinks beneath
-subduction→ the sinking of an oceanic plate at a convergent margin, and the area is
called a subduction zone
-the downgoing plate is called the slab and this subsides into the mantle. This forms
trenches
-water released into the mantle from the heated subducted slab of lithosphere leads to
melting and produces igneous activity at the surface… forming volcanic mountains called
a volcanic arc (this is for ocean-continental)
-when two oceanic plates collide, one subducts under the other and a range of volcanic
mountains rise up along the seafloor rather than the land
-if they reach the surface, they create volcanic island arcs
-the Mariana Trench (ocean continental) formed this way and is the deepest trench of
all
-as these things happen, sediments go toward the trench and can either be scrapped off by
an opposing plate or remains attached to the oceanic plate.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The lithosphere is divided into 20 rigid plates. Tectonic activity is concentrated at plate boundaries, there"s little activity within a plate. Plates move relative to each other and a few centimeters per year. Because of friction between the plates, there"s alternating periods of stasis (stresses build) and movement (when they are released) After a period of stasis, pent-up energy is released suddenly as the plates jump past each other causing earthquakes. When the continents are being pulled apart, faulting occurs and flat-bottomed valleys called rifts form. Divergence of the african and arabian plates has created a system of rifts that radiate from a central point called a triple junction. We"ve determined that earth is not increasing in size, so we revealed that seafloor is consumed at deep-sea trenches about as fast as it is being produced at mid-ocean ridges. Deep sea trenches form when two oceanic plates collide and one oceanic with one continental.
