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زمینشناسی و معدن::
ناحیه پس کمان
backarc region that may have thinned continental
The roll-back causes the island arc to migrate towards the outside of the arc system which in turn results in a strong exten- sion of the backarc region (Fig. 7.5).
continentward-directed in the backarc region (Fig. 7.5).
Potassium-rich calc-alkaline rocks increase in abundance towards the backarc region and eventually pass into shoshonites that are a special type of alkaline rocks.
Because the amount of partial melt in the as- thenospheric wedge decreases towards the backarc region, potassium experiences relative enrichment in the melts although less K is extracted from the subducted material.
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