Chapter 32: Plate Tectonics: A Working Model for the Earth

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(Note: This reading quiz contains some material from lecture that is not found in the textbook.) In this chapter we examine features of the earth that are explained by the plate tectonic model and begin to summarize "how the earth works." The action is always at the plate boundaries. Where plates are moving away from one another, the boundary is said to be (convergent, divergent?) . There are three types of convergent boundary: oceanic crust meets oceanic crust; oceanic crust meets continental crust; continental crust meets continental crust. If the relative motion between two plates is shear motion, the boundary is a "transform boundary." Divergent Boundaries: An important fact seems to be that continental crust does not conduct heat as well as as oceanic crust, so that heat may build up beneath continental crust. A second important fact is that the hydrologic system deposits sediment at the continental edge where its weight bows the strata near the edge of the continent downward to form a so-called "geosyncline." As the heat builds up under a continental mass, it causes a rift (divergent boundary). The energy to drive the plates is thought to come from in the rocks of the mantle which releases heat and causes currents. When the continental pieces begin to move, a forms on the ocean floor at the geosyncline. On the forward edge of the moving continental section, a mountain belt is formed. Pangaea is understood to have come together and formed during the (Paleozoic, Mesosoic, Cenezoic?) Era and began to rift apart thereafter about (20, 200, 2000?) million years ago near the (beginning, end?) of the (Paleozoic, Mesozoic, Cenezoic?) Era. By observing how far apart South America and Africa now are, we can estimate that the continents move a few (centimeters, kilometers?) per year, i.e., about as fast as fingernails grow. A new rift is now forming on the east edge of (Asia, Europe, North America, Africa?) and can be expected to widen over the next 50 million years. The rift begins at a peculiar three-corner pattern. One piece of the rift forms the Red Sea and extends up into Israel to the Dead Sea. A similar thing occurs at the Gulf of California to create the Baja Peninsula. In the northern mid-Atlantic, the midoceanic rift rises above sealevel to form (country?) . Divergent boundaries are characterized by earthquakes that are (frequent, infrequent?) , (shallow, deep?) , (severe, mild?) . Convergent Boundaries (oceanic + oceanic): The classic example occurs at the Aleutian Islands which are an example of a(n) arc paralleled on the ocean floor by a(n) . The island arc represents differentiated material which is (more, less?) dense than basalt and arises from the melt of one of the oceanic plates as it sinks beneath the other. The earthquakes at these boundaries are (frequent, infrequent?) , (shallow, deep, both?) , (severe, mild?) . Convergent Boundaries (oceanic + continental): The classic example is where the plate beneath the Pacific Ocean meets (Asia, South America, Australia?) . On the oceanic side there is a (rift, trench, abyssal plain?) ; on the continental side there is a mountain belt. The continental side is also a region of vulcanism. Mt. St. Helens in Washington state is an example of such vulcanism. The fold mountains formed at these boundaries are eventually eroded, lifting up their granite cores by isostatic adjustments until they become a new piece of the continental . Convergent Boundaries (continental + continental): The classic example is the suturing of (subcontinent?) to Asia resulting in the formation of the (Ural, Himalayan, Andes?) Mountains. The earthquakes at this boundary are (frequent, infrequent?) , (shallow, deep, both?) , (severe, mild?) . The mountains formed at such a boundary are unusually (low, high?) . Transform Boundaries: A classic example occurs in California at the San Andreas Fault. The earthquakes at these boundaries are (frequent, infrequent?) , (shallow, deep, both?) , (severe, mild?) .

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