HOT SPOTS - pretty much do their own thing separate from everything else.Ħ. Very interesting geology occurs along transform boundaries, as all the faulting along the San Andreas fault system in California attests to, but they play a small role in most of the models developed here. Transform Plate Boundaries - where plates slide past one another. Large, explosive volcanos (composite type) are always associated with convergent boundaries.ĥ. Convergent Plate Boundaries - where plates are moving together and crust is being destroyed by descending into subduction zones. New ocean crust forms here, and as long as a divergent plate boundary is active an ocean gets wider.Ĥ. Divergent Plate Boundaries - where plates are moving apart and new crust ( ophiolite suite) is being created. More detailed discussions of the processes happening at the boundaries are explored in the Wilson Cycle and the Tectonic Rock Cycle.ģ. We rely more on illustrations than descriptions.
Most of what is interesting about the earth happens at these boundaries. Typically they are only a couple of hundred miles wide, but may be thousands of miles long. These areas tend to be long, and linear or gently curved areas that are very unstable. PLATE BOUNDARIES- the three ways plates meet and interact. Unlike continents, ocean basins form and disappear quickly the oldest we have is only about 200 million years old (compared to the oldest continent at 3.9 billion.) It is generated at divergent plate boundaries all around the earth, but also disappears down subduction zones at convergent plate boundaries. Technically, ocean basins are composed of the ophiolite suite, a multilayered sequence of rocks. As opposed to continents, ocean basins are composed of relatively heavy mafic rocks like basalt and gabbro, heavy enough they " float" on the earth's hot plastic interior about 5.2 kilometers below sea level. Ocean basins compose the largest surface area on earth. The major exceptions are rims of continental shelf around the edges of the continents. So, when you see a picture of the earth from space, most of that area underwater is ocean basin. Ocean Basins - not everything that is below sea level is ocean basin, but ocean basins are always below sea level. The oldest continental fragment is the Slave province in northwest Canada at 3.9 billion years, but continents are still growing today all around the world.Ģ. Individual continents split apart and rejoin all the time in Wilson cycles. And they tend to grow in size, at least the total mass of continent grows. They had to be created by processes at convergent plate boundaries (subduction zones), but once formed a continent is more or less permanent. When the earth formed, continents did not exist. Continents are composed of felsic and intermediate igneous rocks, like granite and diorite, or their metamorphic equivalents, schist and gneiss. the mid west), and central and western Australia.Ĭontinents are typically sharply separated and distinct from ocean basins, the other major component of the earth's outer shell, on many criteria. Modern cratons are, for example, the interior of North America east of the Rocky Mountains and west of the Appalachian mountains (e.g.
Typically these float no more than a few hundred feet above current sea level, but since sea level rises and falls over time, sometimes sea level is high enough most cratons are below sea level. Geologically they are blocks of relatively light weight rock that " float" above sea level on the earth's hot plastic interior. Cratons (stable continents) - those portions of the earth most of us live on. These tend to be big and boring geologically very little of interest happens within plates.ġ. Below we briefly describe some important features and facts of each.ĬONTINENTS AND OCEAN BASINS - divisions that compose the plates. They can be grouped into three divisions. The six tectonic regimes are the individual components that interact in plate tectonic theory. Plate Tectonic theory is rather complex, and we develop it just enough for someone to understand the basics. Nothing in geology makes sense except in terms of plate tectonic theory. 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 that existed at the time they formed. Plate tectonics is one of the great unifying theories in geology.
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