Although I basically understand, that how the Himalayas formed, it has always confused me how did the vast high Tibetian Plateau came into existence behind it? And what would be its future, is it expected to remain as such for a long time?
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$\begingroup$ I am unsure about the tags, please add them .. $\endgroup$– SawarnikApr 25, 2014 at 17:48
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$\begingroup$ Appears that there might not be a single reason, but many reasons depending on where in the plateau you are looking at; for example, http://geology.gsapubs.org/content/41/4/439.abstract $\endgroup$– blundersApr 26, 2014 at 1:56
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$\begingroup$ There's the handwave-y version that says "rates of orogenic growth and rates of erosion eventually balance, because higher things are exposed to more erosion", plus simple issues of rock strength. However, I'm a volcanologist not a structural geologist; nonetheless if you'd like me to expand on this let me know and I'll type something proper up. $\endgroup$– kaberettApr 29, 2014 at 16:57
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$\begingroup$ @kaberett Ok :) $\endgroup$– SawarnikApr 29, 2014 at 17:26
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$\begingroup$ I can't recall if crustal delamination is applicable to the whole plateau or not. $\endgroup$– SivApr 30, 2014 at 22:16
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1 Answer
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Per yesterday's What-If,
If you make a building too big, the top part is heavy and it squishes the bottom part.
In the context of Tibet, what this means is that rock has a yield strength: pile it up high enough and it will break (via earthquakes); and if you make a big enough pile, especially of continental material, then the concentrations of radiogenic isotopes will be high enough to significantly raise the temperature - and lower the strength - of the rock in question.
In the case of Tibet and the Himalaya, height increase is due to north-south shortening as the Indian plate impacts the Eurasian plate, i.e. the Tibetan plateau initially formed via exactly the same process as the Himalaya. In order to get an approximately stable height, this increase has to be balanced by decrease. The principle processes causing decrease in height in Tibet are:
- east-west extension (see. e.g. Dewey et al. (1988), Tapponnier et al. (1986)), typically along strike-slip faults: this is clearly visible not only in geological maps but also in aerial/satellite photography
- erosion rates increase as topography becomes higher, especially in areas of active mountain-building, in part through a change in which erosion processes are favoured
That the Tibetan plateau is of such uniform height corresponds neatly to calculations suggesting that this is the maximum possible height for such features if they are of typical crustal composition.
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$\begingroup$ Neat. Especially the last paragraph :-) $\endgroup$ May 4, 2014 at 11:35