Geological fieldwork in the southwestern and central parts of the highland complex, Sri Lanka, during 1998-1999, with special reference to the highest grade metamorphic rocks

The field survey of high- and ultrahigh-temperature metamorphic rocks in the southwestern and central parts of Sri Lanka was successfully carried out from December, 1998 to January, 1999. The area of the present study covers the southwestern and central parts of the Highland Complex and certain parts of the Wanni Complex. Systematic sampling was carried out (about 2.5 tons in total) along with field mapping and structural studies. This contribution briefly describes the field occurrences of ten types of metamorphic rocks and two types of charnockite and records the preliminary petrological results of the ultrahigh-temperature (UHT) metamorphic rocks (sapphirine granulites and mafic to ultramafic granulites) in the Highland Complex, Sri Lanka Sapphirine granulites were equilibrated at 900-1000 MPa and 900-1050°C at the peak metamorphic stage and then reached kornerupine-forming conditions at 750 MPa and 800°C through c. 950 MPa and c. 850°C during retrogression. The high-pressure assemblages in mafic and ultramafic granulites (clinopyroxene-garnet-plagioclase, olivine-garnet-clinopyroxene) also show evidence of 1000-1500 MPa at early stage of their metamorphic evolution.