GEOLOGICAL OBSERVATIONS IN HIGH-GRADE MIDPROTEROZOIC ROCKS FROM ELSE PLATFORM, NORTHERN PRINCE-CHARLES MOUNTAINS REGION, EAST ANTARCTICA

Granulite facies rocks on Else Platform in the northern Prince Charles Mountains, east Antarctica, consist of metasedimentary gneiss extensi vely intruded by granitic rocks. The dominant rock type is a layered g arnet-biotite-bearing gneiss intercalated with minor garnet-cordierite -sillimanite gneiss and calc-silicate. Voluminous megacrystic granite intruded early during a mid-Proterozoic (ca 1000 Ma) granulite event, M1, widely recognized in east Antarctica. Peak metamorphic conditions for M1 are in the range of 650-750 MPa at approximately 800-degrees-C and were associated with the development of a gneissic foliation, S1 a nd steep east-plunging lineation, L1. Strain partitioning during progr essive non-coaxial deformation formed large D2 granulite facies south- dipping thrusts, with a steep, east-plunging lineation. In areas of lo wer D2 strain, large-scale upright, steep east-plunging fold structure s formed synchronously with the D2 high-strain zones. Voluminous garne t-bearing leucogneiss intruded at 940 +/- 20 Ma and was deformed in th e D2 high-strain zones. Textural relationships in pelitic rocks show t hat peak-M2 assemblages formed during increasing temperatures via reac tions such as biotite + sillimanite + quartz +/- plagioclase = spinel + cordierite + ilmenite + K-feldspar + melt. In biotite-absent rocks, re-equilibration of deformed M1 garnet-sillimanite-ilmenite assemblage s occurred through decompressive reactions of the form, garnet + silli manite + ilmenite = cordierite + spinel + quartz. Pressure/temperature estimates indicate that peak-M2 conditions were 500-600 MPa and 700 /- 50-degrees-C. At about 500 Ma, north-trending granitic dykes intrud ed and were deformed during D3-M3 at probable upper amphibolite facies conditions. Cooling from peak D3-M3 conditions was associated with th e formation of narrow greenschist facies shear zones, and the intrusio n of pegmatite. Cross-cutting all features are abundant north-south tr ending alkaline mafic dykes that were emplaced over the interval ca 31 0-145 Ma, reflecting prolonged intrusive activity. Some of the dykes a re associated with steeply dipping faults that may be related to basin formation during Permian times and later extension, synchronous with the formation of the Lambert Graben in the Cretaceous.