We appreciate the opportunity that Paterson's comment provides to clarify and emphasize some important points made in the paper. In response to his point 1, we never implied that a single mechanism could explain syntectonic emplacement of granitic magmas. A number of competing mechanisms control magma ascent and emplacement, and our paper explores one mechanism that explains a common relationship between plutons and shear zones.
His point 2 is incorrect and indicates a superficial reading of the paper. First, we did not ignore the older, calc-alkaline suite. We used the fact that this suite is emplaced before shear zone development, and their lobate shape and distribution away from shear zones, to contrast with the en cornue plutons, emplaced later, in the vicinity of active shear zones. In the same rushed fashion Paterson misread the map in Figure 1. In that map, there is a large number of plutons that belong to the early calc-alkaline suite. In other words, there are not “25–30 plutons of the remaining three suites,” there are eight. Out of these, seven have en cornue shapes and are directly related to shear zones.
Point 3 is more interesting. Here Paterson wonders about the tails. We envisage a system where magma flowed initially as sheets within shear zones and that they ballooned outwards from there, into dilational regions of low mean pressures. We used the term tail in a purely descriptive sense to refer to the magma sheet in the shear zone. Magma migration and the feeding of the ballooning pluton is a three-dimensional problem and most of the magma that fed the growing pluton may well have come from underneath the exposed pluton. Unfortunately, due to straining of the tails, we are unable to demonstrate that a magmatic foliation predated solid-state deformation. Therefore we cannot entirely discard the possibility that the tails are parts of the main body of the pluton sheared in the solid-state by the shear zone. However, our main argument is the contrast in distribution of late plutons and the early calc-alkaline plutons. Late plutons lie in the immediate vicinity of shear zones, and early plutons lie away from shear zones.
In point 4 Paterson asks what role magma temperature played and what happens when magma enters the low mean pressure region. We can only speculate about those issues, as they were not part of our models and our speculative views are already expressed in the last paragraph of our original paper (Weinberg et al., 2004, p. 379). I would like to add here that the system is dynamic, and as magma batches intrude low-pressure zones seeking to equilibrate pressure gradients, low pressure is regenerated by the applied external stresses.
Why do we focus on shear zones (point 5)? Because they exert an obvious and direct control on contemporaneous magmatism. Sure, any dilational low mean pressure zone will play a role, but none may develop as strong a pressure gradient as large-scale faults. Finally, in point 6 we are asked to speculate on how the first suite of plutons ascended and why didn't the later plutons ascend in the same way. Since we have not studied the emplacement of the early plutons, I would prefer not to speculate. To answer why the late plutons did not ascend in the same way, I go back to the first point above, that there are a number of alternatives for pluton ascent, and when the variables of the problem changed with the onset of localized shearing, the mechanism changed. The late en cornue plutons could have ascended in a number of ways independently of shear zones. The fact that these plutons, as well as many other worldwide, did not, must be telling us that shear zones play a key role in magma migration and emplacement.