More thoughts from Tom on magmatism and tectonism
If these ideas do not satisfy you or you think I'm just full of it, spend some time walking through an exposed pluton. Look closely! Whether it is ultramafic, intermediate or silicic in composition it will be chock full of structurally enigmatic folds, foliations, and crosscutting fabrics. What do these structures really mean? Personally, I doubt that they are all related to emplacement and/or settling processes during construction of a single or multi-stage magma chamber.
Another particular problem is that most shallow (<10 km) plutonic bodies do not record much strain in the final stages of crystallization. From an intuitive standpoint, it seems that plutons, or any blob 'o' magma for that matter, should be relatively weak areas (i.e. strain blotters) within an active orogen. So why don't they record the strain we expect? When they do record strain, is there any relationship between that strain and the overall regional strain?