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GEOLOGY 12
STUDY GUIDE
CHAPTER 9 PLATE TECTONICS
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Major Concepts
1.
The concept of continental drift was based on geologic evidence available to scientists
in the 1910s and 1920s. although the idea was not taken seriously by most geologists
until the 1960s.
a. The apparent fit of the continental margins of Africa and South America first
suggested the notion of continental drift. (see p.176)
b. Findings of similar fossil species and climatically sensitive rocks on several
continents further supported continental drift. (see p.177)
c. The notion of continental drift lacked a plausible mechanism or cause for
continental motions. (see p.178)
2.
The modern view of the earth's structure calls for "plates" of rigid lithosphere, which
may contain continents, to "float:" on a semi-solid, mobile asthenosphere within the
mantle.
a. The lithosphere consists of the crust, both oceanic and continental, plus the rigid
upper-portion of the mantle. (see p.178)
b. The asthenosphere is the semi-solid zone of the mantle which is capable of
"plastic" movement beneath the lithosphere. (see p.178)
c. The lithosphere is cracked or fragmented into a number of plates. (see p.178)
d. The boundaries of the plates are marked on the globe by linear bands of
earthquake and volcanic activity. (see p.179)
3.
An enormously varied amount of data has accumulated in support of the theory of
plate tectonics.
a. The mid-oceanic ridges represent sites of the creation of seafloor. (see p.180-181)
b. The record of paleomagnetism preserved in seafloor rocks reveals a pattern of
seafloor spreading away from mid-oceanic ridges. (see p.181-182)
c. The ages of the ocean floors confirm that the seafloor becomes older as one
moves away from the mid-oceanic ridges. (see p.183)
d. Polar-wander curves, deduced from paleomagnetic data from ancient continental
rocks, indicate the directions continents have moved through time. (see p.184)
e. Reexamination of the jigsaw puzzle" fit of continents continues to support the idea
that continents were once joined together and have since separated. (see p.184-185)
f. The reconstructions of plate motions indicate that all the continents were joined in
a single supercontinent which began to break up about 200 million years ago.
(see p.185)
4.
Plate boundaries are defined by the nature of the motions which occur along them.
a. At divergent boundaries, plates are moving apart from one another and new crust
is created. (see p.186)
b. Transform faults are frequently associated with divergent boundaries; along the
fault the plates are sliding past one another. (see p.186)
cont’d…
c.
Convergent boundaries occur when two plates are colliding; a variety of situations
may arise depending on the sort of lithosphere and crust involved in the collision.
(see p.187-189)
5.
Rates of plate motions can be calculated from several data sources.
a. For rocks of known ages, rates of motion can be calculated with reference to
distance from spreading ridges. (see p.190)
b. The locations and ages of hot spot volcanoes also can be used to derive plate
motion rates. (see p.190-191)
c. Rates of motion vary greatly about the globe. (see p.191)
6.
The theory of plate tectonics is useful in understanding a great number of geologic processes, although we do not yet understand what causes the plates themselves to move.
a. Convection cells in the asthenosphere or lithospheric "pull" are two possible
causes of plate motions. (see p.191-192)
b. Plate tectonic processes can be applied to explain continental motions for nearly 2
billion years, and perhaps for a longer time. (see p.192)
c. Plate tectonic activity explains many of the rock "transformations" in the rock
cycle. (see p.192-193)
Terms and Phrases
Aleutian Islands
continent-continent collision
Curie temperature
dip needle
Glossopteris fossil plant
Hawaiian Islands
hot spots
magnetic lines of force
magnetic reversals
mid-oceanic rift zone
paired metamorphic belts
Pangaea
polar-wander curves
pulling apart
Red Sea
reversed polarity
San Andreas fault
subduction zone
volcanic island arc
Introductory Assignments
1.
2.
3.
4.
5.
Highlight new terms used in the Major Concepts section above.
Define or explain the terms and phrases listed above.
Rewrite the Summary on page 194 in point form.
Review chapter by paying special attention to the diagrams, photos and their captions.
Read text for clarification.
Use the Main Topics below to complete the Chapter 9 Study Guide Quiz.
Main Topics
1.
2.
3.
4.
Which terms or phrases are related specifically to paleomagnetic evidence for
continental motions and seafloor spreading?
Which terms or phrases are related to divergent and / or transform fault plate
boundaries?
Which terms or phrases are related to convergent plate boundaries?
Which terms did not apply to any of the preceding questions?
Chapter 9
Study Guide
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