[S-CG52] Petrology, Mineralogy & Resource Geology

[SCG52-P07] Neoproterozoic arc magmatism and high-grade metamorphism of the basement rocks in southern Malawi

*Toshiaki Tsunogae¹, Sam Uthup¹, Mzee Wandembo Nyirongo², Md. Sazzadur Rahman¹, Yusuke Takamura¹, Kazuki Takahashi¹ (1.University of Tsukuba, 2.Malawi University of Science and Technology)

Keywords:Mozambique Belt, Kuunga Orogen, East African Orogen, Granulite, Phase equilibria modeling

The basement rocks in southern Malawi form part of the Mozambique Belt (or the southern Irumide Belt) that correspond a typical example of Neoproterozoic collisional orogens in southeastern Africa. The dominant lithologies in Lilongwe-Zomba-Blantyre area in southern Malawi are biotite gneiss (biotite + quartz + microcline + plagioclase), charnockite (orthopyroxene + K-feldspar + quartz + plagioclase + ilmenite + magnetite), and mafic granulite (plagioclase + clinopyroxene + garnet + calcic amphibole + quartz + orthopyroxene + ilmenite) which are intruded by syenite (K-feldspar + calcic amphibole + biotite + quartz + clinopyroxene) and granite (quartz + K-feldspar + plagioclase + biotite). Garnet in the mafic granulite is often mantled by plagioclase + orthopyroxene coronae, suggesting post-peak decompression. Phase equilibria modeling of the mafic granulite in the system NCKFMASHTO yielded the peak metamorphic condition of 800-920 ^oC and ~10 kbar with a clockwise P-T evolution. Major, minor, and REE geochemical data for selected felsic orthogneisses suggest arc-magmatic signatures of the rocks. The results of this study suggest that the orthogneisses in southern Malawi corresponds to a Neoproterozoic magmatic arc unit that was probably metamorphosed at high- to ultrahigh-temperature conditions during the latest Neoproterozoic East-African and Kuunga orogens.