The distinction between pre-, syn-, and post-kinematic granites in three dimensions, in pressure-temperature space, and in time becomes critical.In particular, mapping of macro- and micro-structures combined with precise U-Th-Pb dating of migmatitic leucosomes and granitic rocks in deformation zones can be used to constrain the relative timing of metamorphism, melting, ductile shearing and brittle faulting.
The channel flow hypothesis for the Greater Himalayan Sequence fits all known geological (Searle et al., 2003, 2006, 2010b; Law et al., 2004, 2006, 2011) and geophysical (Nelson et al., 1996; Hauck et al., 1998; Tilmann et al., 2003) parameters. (2001) using all the Himalayan-specific geological and geophysical parameters shows that Miocene mid-crustal channel flow along the Himalaya is a viable process.
Exhumed sections of migmatites are beautifully exposed in the middle crust of old orogens such as the Proterozoic Wet Mountains of Colorado and young Tertiary–active orogens such as the Himalaya and Karakoram.
Migmatites and leucogranites occur both on a regional scale (e.g., Greater Himalayan Sequence) and along more restricted shear zones and strike-slip faults (e.g., Karakoram, Jiale, and Red River faults).
Melting and deformation are clearly diachronous across orogenic belts over space and time, yet in general, deformation must precede regional metamorphism and melting in order to thicken the crust and increase pressure and temperature.
Some deformation can be synchronous with partial melting and there is almost always post-melting deformation along shear zones or faults.