The crustal origin of many granitic plutons in the accretionary orogenic belts is still a controversial point of view. The assumed contribution of the (lower) or the (middle) crust in the genesis of the granitic plutons especially, the high-K calc-alkaline ones (A2 of Eby) contradicts with their wide distribution in the juvenile continental crust (e.g.Arabian-Nubian shield).
One idea: Perhaps delamination of lower crust is underestimated as a factor in accretionary orogens and the contribution of a mafic lower crust to the origin of granitic melts is overestimated. If you consider stacked middle crust as the main source for such magmas this might lead to a better explanation of the observed high-K calc-alkaline chemism.
http://scholar.google.de/scholar?q=%22lower+crust+delamination%22
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