Plate Tectonics CPR Paper
by
The Professor
Introduction
Plate tectonics is a very important theory. The purpose of this assignment is to write about the plate tectonics of two regions in the Pacific Ocean. Plate tectonics is a theory that explains how oceanic plates move on the earth and how they form mountain chains, trenches, and volcanoes. [:(Cmnt by William Prothero: This introduction doesn't specify a topic for the investigation. It is clear that the author intends to make a "book report" about plate tectonics. ):]Methods
The theory of plate tectonics was first propsed by Alfred Wegener in 1912. Wegener used the fit of the continents, the distribution of fossils, a similar sequence of rocks at numerous locations, ancient climates, and the apparent wandering of the Earth's polar regions to support his ideas. He used his observations to hypothesize that all of the present-day continents were once part of a single supercontinent called Pangaea. {link: pt_glblPlates.jpg}Figure 1 shows a map of the earth's plates [:(Cmnt by William Prothero: Methods are not discussed here. The author launches into a book report which is related to the assignment, but ignores the required content for this heading. ):] .Observations
{link: pt_subzone.jpg}Figure 2 shows a diagram of a convergent plate boundary and {link: pt_sprdMdl.jpg}figure 3 shows a map of a divergent plate boundary. The theory of plate tectonics states that the rigid plates, called the Lithosphere, move over a viscous base material called the Asthenosphere. {link: pt_subzone.jpg}Figure 2 illustrates how the lithosphere of one plate descends beneath the lithosphere of the opposing plate, forming volcanic islands. The volcanic islands are formed from melting crust as it descends into the mantle. The crust melts because the water it contains lowers the melting point of the rock, which melts and rises to the surface to form the volcanoes.An oceanic divergent margin means that the plates meet and disperse in opposite directions. The resultant gap from these diverging plates is filled up with uprooted, low density magma. This process leads to the series of volcanoes which form into a ridge in the gap left by the plates. This process is known as sea floor spreading. This is also illustrated in {link: pt_sprdMdl.jpg}figure 3. The aging crust then sinks steadily down, while the mountains in the ridge slowly move outward while new ones fill in their place. The mountains move in the direction of the plat [:(Cmnt by William Prothero: The figures used here are copied from web pages. The assignment instructions required an author generated sketch. Moreover, the author provides no observations at all and continues in a book report mode. ):] e.
Interpretations
My study shows that Region A, which has a lot of quakes and volcanoes along a trench, is a convergent plate boundary. It also shows that Region B, which is a ridge with few quakes and a young age, is a divergent plate boundary. This conclusion is proven by the data from the "Our Dynamic Planet" CDROM and Prof Prothero's lab book for Oceanography [:(Cmnt by William Prothero: These interpretations are correct, but are completely lacking in support from earth data, which was the point of the assignment. ):] .References
Material was extracted from http://volcano.und.nodak.edu/vw.html. 200 [:(Cmnt by William Prothero: This is a good reference to the web site where the images were taken from. It is unfortunate that the author chose to ignore the assignment instructions, however.):] 4.Map of the earth's plates {fig: pt_glblPlates.jpg}
Model of a subduction zone. {fig: pt_subzone.jpg}
Cross section of a spreading center. {fig: pt_sprdMdl.jpg}