And A Plate Tectonic Rock Cycle
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How Much Do You Understand - A Self Test
One Page Wilson Cycle Circular Wilson Cycle Published Wilson Cycle Stage A - Stable Craton Stage B - Hot Spot/Rifting Stage C - Early Divergent Margin Stage D - Full Divergent Margin Stage E - Volcanic Arc Mtn. Bldg Stage F - Isl Arc/Continent Collision Stage G - Cordilleran Mtn. Bldg. Stage H - Continent-Continent Mtn. Bldg. Stage I - Stable Continental Craton Other Related Links
A Plate Tectonic Rock CyclePage of all cross sections Igneous Home Page Sedimentary Home Page Metamorphic Home Page Plate Tectonic Primer The material is copyrighted (text, images, etc.), but may be used by anyone for personal or educational purposes so long as the source is acknowledged. Lynn S. Fichter © 1999 (Fichtels@jmu.edu)  Department of Geology and Environmental Studies (Geology home page jmu.edu/geology/) James Madison University, Harrisonburg, VA 22807 Spring, 1999 |
The Cyclical Opening and Closing of Ocean Basins
No rock is accidental. No idea in geology is more
profound than this; it runs from the center to the whole of geology and influences every subdiscipline
of the field. Genuine understanding of the science of geology begins with one's ability to
understand and explain why no rock is accidental.Tectonics is concerned with deformation in the earth and the forces which produce deformation. Plate tectonics is the theory that the earth's lithosphere (outer rigid shell) is composed of several dozen "plates", or pieces, which float on a ductile mantle, like slabs of ice on a pond. In plate tectonic theory earth history, at its simplest, is one of plates rifting into pieces diverging apart and new ocean basins being born, followed by motion reversal, convergence back together, plate collision, and mountain building. This cycle of opening and closing ocean basins is the Wilson Cycle. Plate tectonics is one of the great unifying theories in geology. Virtually every part of the earth's crust, and every kind of rock and every kind of geology can be related to the plate tectonic conditions which existed at the time they formed. Nothing in geology makes sense except in terms of plate tectonic theory. One of the most important messages of modern understanding of plate tectonics and the Wilson cycle is that beginning with a parent igneous rock of mafic/ultramafic composition all the other rocks now on the earth can be generated. The most important message of the plate tectonic rock cycle is that each and every rock forms only under a specific set of tectonic conditions. Most geologic activity occurs at the three kinds of plate boundaries: (1) divergent boundaries where plates are moving apart and new crust is being created, (2) convergent boundaries where plates are moving together and crust is being destroyed, and (3) transform boundaries where plates slide past one another. Very interesting geology occurs along transform boundaries, as all the faulting along the San Andreas fault system in California attests to, but this model does not include transform boundaries. We have two models summarizing earth evolutionary processes. (1) The Wilson Cycle, explored below, and . . . (2) The Tectonic Rock Cycle, a more theoretically abstact model of how rocks and the earth evolve. The following Wilson Cycle model follows the series of cross sections constituting the Wilson cycle. It begins with a hypothetical geologically (tectonically) quiet continent. The model is divided into nine stages, but the stages are arbitrary and do not exist naturally. The earth is an ongoing series of processes so it is much more important to understand the processes, how they are related, and how one process leads naturally to the next process. Also note that this Wilson Cycle is a simple, ideal model. The earth has many continents, which migrate across its spherical surface in very complex ways. Just about any scenario you can think of, and any exception you can imagine is quite possible - and has probably happened during some point in the earth's history.  Go to Stage A PDF version of illustrations for all stages The Plate Tectonic Rock Cycle
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