The origin of the pink granites of Sri Lanka — another view

Pink granites are common throughout the Precambrian metasedimentary terrain of Sri Lanka and play a significant role in reconstructing the geologic evolution of this country. Essentially microcline-bearing rocks, they form conformable layers with the associated metasedimentary rocks and are always interlayered and associated with rocks possessing amphibolite-facies mineral assemblages. This association is seen throughout the terrain at all scales. Further, they always tend to fold around the major structures of the terrain and contain conformable layers and enclaves of rare metasediments, and have a gneissic appearance in places. Their field relations, associations, mineralogy, petrography, petrofabrics, chemistry, and also age, suggest that they are metasediments, probably arkoses, which have undergone the same set of metamorphic and deformational events as other Precambrian metamorphic rocks of Sri Lanka. Their present ‘granite-like’ character does not necessarily imply that they are the products of crystallization of magmatic or anatectic melts, or that they have had a replacement origin. Rather, chemical composition has determined their present ‘granite-like’ character, due to granitization by simple isochemical recrystallization — “Treptomorphism” — during highgrade metamorphism, at a P_H2O which was sufficient to retard their grade to amphibolite facies under granulite facies metamorphic conditions, at which the other metasediments of Sri Lanka have metamorphosed.