The paradoxical aspect of the Himalayan granites

Abstract

The Miocene leucogranites at the top of the crystalline High Himalaya are commonly cited as reference examples of collision-related granites. However, they are much smaller than the Hercynian collision-related granites. Additional comparison with magmatic arcs and cordilleran-type batholiths emphasises the low rate of magma production for the Himalayan granites. We review and summarise data on the condition of segregation, ascent and emplacement of leucogranitic magmas in the High Himalaya. The plutons are small and mostly concordant with the country rocks. Thermal data indicate that they were emplaced within the ductile crust. Magma ascent and segregation has been strongly controlled by the extrusion of the High Himalaya Crystallines. Strain during extrusion provided the magma its internal high anisotropy, while aggregation of successive pulses of magma coming from chemically different sources caused chemical heterogeneity. The source region had a slow melting rate (< 13 %) at rather low temperature (below 780 °C).