plate boundary一問？？？？？？？？？？

以下係世界上各種margin的例子，而箭嘴（→）後是所形成的地形：
1. destructive / convergent plate boundary （→←）
South American plate & Nazca plate → Andes
Caribbean plate & Cocos plate
North American plate & Juan de Fuca plate → Rockies
North American plate & Pacific plate
Pacific plate & Philippine plate
Pacific plate & Indo-Australian plate → Islands arcs of the west Indies & Aleutians
Eurasian plate & Arabian plate
Eurasian plate & African plate
Eurasian & Indo-Australian plate → Himalayas
Arabian plate & African plate → East African Rift Valley

2. constructive / divergent plate boundary（←→）
Cocos plate & Nazca plate
Eurasian plate & North American plate → Mid Atlantic Ridge
South American plate & African plate → Mid-Atlantic Ridge
Pacific plate & Nazca plate → East Pacific Rise
Pacific plate & Cocos plate
Pacific plate & Juan de Fuca plate
Pacific plate & Antarctic plate
Indo-Australian plate & Antarctic plate
Indo-Australian plate & African plate
African plate & Antarctic plate
African plate and Arabian plate
3. conservative / passive plate boundary
（→
　←）
Pacific plate & North American plate → the San Andreas Fault


圖片參考：http://i51.photobucket.com/albums/f382/kookaburrawing/questions/mapboundary.png?t=1201442814

圖一‧World plate boundarymap (source: 1)

參考資料:
1. Wikipedia -- plate tectonics (地圖)
2. 黎海天《Topics on Certificate Geography Book 1》
3. 其他網站

There are only two types of plates: continental plate and oceanic plate.The six major lithospheric plates are :American, Eurasian, Indian, African, Pacific and Antarctic.

There are 3 kinds of plate boundaries:

1. Divergent Boundaries:

During process of sea floor spreading, there occurs oceanic ridges and new oceanic crust.

the formation of the new crust on either side of the vents would act to push plates apart, as we see at the Mid-Atlantic Ridge, which helps to move North America and Europe further and further apart. Mid-ocean ridges are vast mountain chains in the ocean and are as tall if not taller than mountain chains on land. The process which actually drives the motion at these ridges is known as convection. Magma is pushed upwards through the ridge cracks by convection currents. As some magma erupts out through the crust, the magma which does not erupt continues to move under the crust with the current away from the ridge crest. These continual convection currents, called convection cells, help to move the plates away from each other to allow more crust to be created and the sea floor to grow.


2. Convergent Boundaries:

Subduction zones are the location of very strong earthquakes, which occur because the action of the down going slab interacts with the overriding slab.

The "Ring of Fire" around the margins of the Pacific Ocean is due precisely to the subduction zones found around the edges of the Pacific plate. Subduction also is the cause of the volcanic activity in places like Japan: as the downgoing slab goes deeper beneath the overriding plate, it becomes hotter and hotter because of its proximity to the mantle. This causes the slab to melt and form magma, which moves upward through the crust and eventually forms volcanoes (island arcs) in oceanic crust or huge intrusive masses (plutons and batholiths) in continental crust. The Aleutian Islands are another example of a surface expression of subduction.

Sometimes, when there is a convergent boundary between two continental plates, subduction cannot occur. Since continental crust is more bouyant, or less dense, than oceanic crust, one plate does not easily override the other. Instead, the plates crumple as they plow into one another, and a very high mountain range is created. This is a special type of convergent boundary called a collisional boundary. The Himalayas in India are the result of two continental plates (the Indo-Australian and Eurasian plates) colliding head on.

3. Conserative Boundaries:

This is the margin at which the plates neither gain or lose the surface area, but simple slip past each.

The classic example of a transform plate boundary is the San Andreas fault in California. The North American and Pacific Plates are moving past each other at this boundary, which is the location of many earthquakes. These earthquakes are caused by the accumulation and release of strain as the two plates slide past each other. Another example of a transform boundary is seen at the mid-ocean ridges, where the spreading centers are offset by transform faults anywhere from a few meters to several kilometers in length.