Plate tectonics and the structure of the Earth's crust
To be followed in Topic:Plate tectonics.
See articles on w:Plate tectonics and planetary w:Crust (geology).
The theory of plate tectonics has been around for about 50 years, it can explain many phenomina like mid w:oceanic trenches, large scale volcanic mountain ranges and deep and shallow seeded earthquacks. But w:mantle plumes, underwater mountain ranges, guysers etc are harder to explain. As we continue to gather knowledge we could one day get a full picture of how our earth functions and to predict dissasters before they happen.
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[edit] What is a tectonic plate
A tectonic plate is the crust of the planet that is divided by fault lines, all oceanic and continental rock is part of of a tectonic plate down too and including the upper mantle, this is the w:lithosphere. The centre of a tectonic plate is an area of moderatly stable crust without a high frequency of earthquacks, volcanoes and plate instability are associated with areas close too and including plate boundries, though it can not be said that they do not occure within the centre of the plate. The plate is made up of two catgories of rock, that of continental rock and oceanic rock. See the articles for a description.
[edit] Plate boundry
[edit] Convergent boundary
A w:convergent boundary is a section of a plate that is moving towards and colliding with another plate. A good example is the w:Indian plate moving north into the w:Eurasian plate forming the w:Himalayas. There are three types of plate convergence, oceanic-oceanic convergence: where the colder denser plate subductes under the other less dense plate (Pacific plate subducting under the Australian plate north of New Zealand, but the Australian plate does subduct under the pacific plate in other areas), Oceanic-continental: where the oceanic plate subducts under the continental plate (Nazca plate subducting under the South American plate), and continental-continental convergence (Indian plate is moving north wile the Eurasian plate is moving south).
[edit] Divergent boundry
This is where two or more plates are separating and moving in different directions. At the center of the divide is a rift. A rift is an area of continent where one plate has started to divide in two. This then forms a rift valley whicn eventually forms a mid oceanic ridge where new plate is being formed. Each plate is usually going in opposite directions. As the oceanic rift is not continuous, but is fractured and there is a seperation of transforming boundaries of many kilometers between the fractures[1]. These seperated fractures are connected by w:transforming boundries. So an upwell of w:magma might not take place at close trenches at the same time, causing the same plate to be moved independanty at different divergent centers. Fractures caused by this displacement can continue for many kilometers, sometimes many hundreds into the plate.
[edit] Transforming boundry
These type of plates are moving past each other, they are the least numerous of the plate boundaries, but as in the San Andreas fault, can be quite devastating.
[edit] The role of convection
[edit] Major types of rock produced
There are various ways rocks are formed, the major ones are sedimentary and igneous with metamorthic being either of the two as precursors.
For Igneous rocks there are two main types, that classed as basaltic and granitic. The former occures mainly on continental and the later is the predominant rock forming the ocean bedrock.
[edit] Minor types of roeck produced
[edit] Readings
Sedimentary rocks
- http://earthds.info/pdfs/EDS_05.PDF Sedimentary rocks.
- http://danling.com/earthling/geo/Chapter%206%20Outline%20-%20Sedimentary%20Rocks.pdf
Igneous rock
- http://earthds.info/pdfs/EDS_04.pdf Igneous rocks
- http://msnucleus.org/membership/html/jh/earth/igneous/jhigneous.pdf Igneous rocks 2
Metamorphic rock
- http://earthds.info/pdfs/EDS_06.PDF Metamorphic rocks
Other rock types
