The Trans-Hudson Orogen (THO) of North America and the

Paleoproterozoic and Cenozoic record, respectively, of continent-continent collision that is notably similar in scale, duration, and character (St-Onge et al. 2006). In THO, the tectonothermal evolution of the lower-plate involves (1) early thin-skinned thrusting and Barrovian metamorphism, (2) out-of-sequence thrusting and high-T metamorphism, and (3) fluid-localized re-equilibration, anatexis and leucogranite formation. The crustal evolution of the Indian lower-plate in HKTO involves (1) early subduction of continental crust to UHP (ultra-high pressure) eclogite depths, (2) regional Barrovian metamorphism, and (3) widespread high-T metamorphism, anatexis and leucogranite formation. The shallow depths of the high-T metamorphism in HKTO are consistent with early to mid-Miocene ductile flow of an Indian lower-plate mid-crustal channel, from beneath the southern Tibetan plateau to the Greater Himalaya. Melt weakening (Jamieson et al. 2004) of the lower-plate in THO is not observed at a similar scale probably due to the paucity of pelitic lithologies, and consequently formation of a mid-crustal channel is not required to account for the documented tectonothermal evolution of THO’s lower plate. Tectonothermal events in the upper-plate of both orogens include pre-collisional accretion of crustal blocks, with for example the North Atlantic craton of Greenland and Canada being in a similar tectonic position to the South China block in Asia (St-Onge et al., 2008), emplacement of cumulative Andean-type plutonic suites, and consequent, multiple phases of high-T metamorphism (St-Onge The Trans-Hudson Orogen of North America and the Himalaya