Geology Of Central Madagascar – First Expedition

Madagascar occupies an important location within the East African Orogen (EAO). The EAO involves a collection of Neoproterozoic microcontinents and arc terranes wedged between older cratonic units during the final assembly of the supercontinent Gondwana. The Malagasy basement preserves a record of the timing and style of amalgamation of Neoproterozoic India (Dharwar Block) with the Congo Block during the final closure of the Mozambique Ocean.

Central Madagascar is comprised of a number of Precambrian units. The oldest blocks, the Antongil and Masora Cratons consist of Mesoarchaean ortho- and para- gneiss cores in addition to Neoarchaean granitic and metasedimentary rocks. The largest unit, the Antananarivo Block underlies the central highlands and consists of Neoarchaean granite interlayered with voluminous Cryogenian to Cambrian granite, syenite, and gabbro, much of which has subduction zone geochemical characteristics. Overlying the Antananarivo Block are the Itremo-Ikalamavony, Ambatolampy, Vondrozo and Manampotsy groups.

The target of this research is within Itremo-Ikalamavony Group which consists of probable Palaeoproterozoic greenschist- to amphibolite- facies metasedimentary rocks and is intruded by Cryogenian syenitic to granitic rocks and gabbro. The aim of this project is geological reconnaissance of the source area of the metasediments. Therefore, the understanding of the nature and the tectonic configuration of the previous basin through structural and petrography analyzes and geochronology data.

This field work in Madagascar brought together researchers from Australia, Madagascar and Brazil: Alan Stephen Collins (Australia), Donnelly Brian Archibald (Australia), John Foden (Australia), Theodore Razakamanana (Madagascar) and Raisa Lopes Costa (Brazil).