Dynamics associated with the Indus-Yarlung Suture Zone threaten China weeks after the deadliest earthquake in that nation's modern history. This week's aftershocks, measuring as great as 5.0 on the Richter scale, impede relief efforts and showcase the instability of the Tibetan Plateau. A suture zone is defined as the area of collision between two continental tectonic plates. There are several active suture zones in the world, but the recent collision between the Indian and Eurasian plates is a perfect example.
There are three basic ways in which the two tectonic plates can interact. First, there can be divergence or rifting and the forming of new oceans. There can also be lateral displacement or strike-slip faults, as observed by the infamous San Andres fault in the continental United States. Finally, there is a convergent plate boundary, which is associated with the subduction of oceanic plates and collision of continental plates.
Continental plates differ from ocean plates by composition, thickness and behavior. They are composed of lighter silicate material that is buoyant, and which floats on the dense mantle material. They are also considerably thicker than oceanic plates. When the buoyant large land mass converges with another plate, it will either subduct the denser oceanic plate or resist subduction itself by forming accretionary prisms and suture zones. The lighter material is always pushed back towards the surface due to a density gradient.
When a collision of continental plates occurs, there are a series of events that take place over millions of years until the two land masses merge together, forming a larger tectonic plate that will behave as a single object. During the preset, there is an approaching land mass with related continental shelf and ocean plate material that is subducted by the larger plate. Then, as the lighter buoyant continental plate material approaches, there is resistance to the subduction complex, accretion of material and the creation of a suture zone.
The suture zone - area of collision - has a tremendous amount of stress related with it. Low angle thrust faults displace the buoyant material. The formation of excessively thick plate material and large mountains creates a very unstable environment. Heavily folded rock bands and metamorphic rocks known as mylonites help describe the high-stress, low-temperature rock alterations that occur. Erosion rates are significantly high and the young unstable mountain chains are prone to failure. The high-stress environment is relieved temporarily by the large earthquakes, as observed in China and the Tibetan Plateau.
A suture zone is, without a doubt, one of the most geologically unstable environments known to humanity.
References:
http://en.wikipedia.org/wiki/Indus-Yarlung_suture_zone
http://www.alcwin.org/Dictionary_Of_Geology_Description-236-S.htm
http://www.ipgp.jussieu.fr/~cogne/pub/site_perso/Mes%20papiers/1993_Configuration_Asia.pdf
http://tectonics.caltech.edu/publications/pdf/BettinelliJGEOD2006.pdf
http://en.wikipedia.org/wiki/Plate_tectonics
http://www.seismo.unr.edu/ftp/pub/louie/class/100/plate-tectonics.html
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