GEOL 1 Lecture Notes - Lecture 3: South American Plate, Mantle Convection, Convergent Boundary

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Published on 19 Oct 2020
Jeff Koo
Geol 1
Physical Geology
Spring 2019
4 Units
Continent- continent collision pg.18
-continental lithosphere is much less dense than the mantle below and therefore neither plate
subducts. Continent-continent is preceded by oceanic-continental convergence
- Ocean ridge- india & Asia
- India-Himalayas (change in height)
- How is this magma produced?- mantle fluxing
Evidence of plate motion
- Plate motion can be directly measured using satellites, radar, asers and global positioning
o Measurements accurate to within 1cm
o Motion rates closely match those predicted using sea floor magnet
What causes plate motions? Pg.516
- Causes of plate motion are not yet fully understood, but any proposed mechanism must
explain why:
o Mid-oceanic ridges are not elevated, while trenches are cold and deep- most
divergent boundaries coincide with the crests of submarine mountain ranges it is
higher than the deep ocean floor
o Ridge crests have tensional cracks
o The leading edges of some plates are subducting sea floor, while others are
continents (which cannot subduct)
Mantle convection may be the cause or an effect of circulation set up by ridge push
and/or slab-pull
Convergent plate boundary
The second type of boundary, by accommodating the addition of new sea floor at
divergent boundaries, the destruction of old sea floor at convergent boundaries ensures
the earth does not grow in size.
- Andes mountain range, where the Nazca plate is subducting beneath the south American
plate, and the Cascade Range of Washington, Oregon, and northern California.
- Convergent boundaries by the character of the plates that are involved: ocean-continent,
ocean-ocean, and continent-continent.
Transform boundaries pg. 19
- Two plates slide horizontally past each other, neither toward nor away from each other
- Crust is neither produced nor consumed
- Surface features are offset
- Earthquakes occur
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