Granulite facies metamorphism of the metasediments from Tallaksenvarden and Starheimtind nunataks, central Dronning Maud Land (cDML), East Antarctica and their correlation with the eastern granulites of the East African Orogen (EAO)

Abstract

There are eight nunataks in cDML exposed through the vast expanse of the ice sheet between Schirmacher Oasis and the Gruber–Wohlthat Mountains. Tallaksenvarden and Starheimtind are two important nunataks that mark the eastern and western limits of their exposures. There is paucity of the metamorphic data from these nunataks which otherwise lie between the well-studied Schirmacher Oasis and Humboldt Range. These nunataks comprise a sequence of granulite facies metasedimentary rocks interlayered with pyroxene granulite. The granulite facies assemblage in the pelitic granulite is garnet + sillimanite ± kyanite + biotite + quartz + perthite ± plagioclase ± rutile ± ilmenite. P-T-t path estimations reveal ultrahigh temperature (UHT) metamorphism (M₂, ca.630-570 Ma) with a clockwise path (>900 °C at ≥8 kbar) during the Cryogenian-Cambrian period well above the wet granite solidus for incongruent melting with significant increase in melt volume during decompression. Yttrium in garnet thermometry combined with textural evidence (symplectitic quartz, biotite and plagioclase embayment in porphyroblasts) suggest initiation of porphyroblasts growth in the pelitic granulite at c. 550 °C with continued growth during increase in temperature (∼645 °C) followed by resorption and growth coinciding with increased melt generation. These nunataks and Schirmacher Oasis expose the same lithopackage with identical metamorphic and structural evolution possibly extending southward till the inland mountains of the cDML. This study also identifies that these nunataks indeed represent a portion of the EAO with a possible transpressive deformation regime.