[S-MP24] Supercontinents and Crustal Evolution

[SMP24-05] Petrology, metamorphic conditions, and monazite dating of metapelites of the Zambezi Belt supracrustal sequence, Zambia

*Kabangu Grace Sakuwaha¹、Toshiaki Tsunogae¹ (1.University of Tsukuba)

キーワード：Zambezi Belt, Zambia, Metamorphic P-T, Monazite dating

The Zambezi Belt located in southern Zambia forms part of E-W trending late Pan-African Kuunga orogen associated with assembly of Gondwana supercontinent. Lithologic units of the belt include Neoarchean to Neoproterozoic granitic basement, unconformably overlain by supracrustal sequences, consisting of meta-pelites, psammites, calc-silicates, marbles, and magmatic rocks with NE-SW shortening. Several studies have been conducted to determine the metamorphic conditions of separate localities within this region but data on the textural context to directly link metamorphic paragenesis to geochronological data is limited. We present the first texture-based age determinations of the metamorphism of the metapelite sequence located between the Mpande and Ngoma basement terrains. The data presented includes petrology, metamorphic P-T conditions and geochronological data obtained by in-situ microprobe techniques on monazite to link metamorphic paragenesis to key tectonic events in the Pan-African orogeny. The studied rocks exhibit penetrative foliations with mineral assemblages consisting of garnet, biotite, quartz, kyanite, ± staurolite, muscovite, and chlorite or kyanite, biotite, muscovite, chlorite and quartz with accessory rutile, ilmenite, tourmaline, and monazite. Application of garnet-biotite geothermometers on appropriate samples yields peak metamorphic P-T conditions of 572 - 627°C and 4 - 6.2 ± 1.3 kbar. Application of CHIME age calculations on monazites identifies two age populations which potentially represent long-lived metamorphism from ca. 630 and 573 Ma. These ages are also nearly consistent with previously reported ages from other localities within the belt which have been interpreted to correspond to collisional orogenesis and closure of the Mozambique ocean, followed by burial metamorphism prior to exhumation and erosion.