INTEGRATED STRUCTURAL AND LANDSAT STUDIES OF THE BETSIMISIRAKA SUTURE, EAST MADAGASCAR

Madagascar is one of the key areas to understand the development of the East African Orogen and it contains a proposed collision zone between East and West Gondwana. Kroner et al., defined an important shear zone in 2002, and argued that it can be a suture zone, and he named it the Betsimisaraka Suture (B.S). Focusing on that suture zone, many questions need to be answered such as: what is the nature of the BS?, and how big is the B.S?, Does it contain relicts of Proterozoic ocean crust and mantle (Mozambique ocean)? Does it join once separated East and West Gondwana fragments? Can we deduce the sense of convergence by examining both the large scale and meso-scale kinematic indicators within the suture? In consequence, to answer those questions: structural and remote sensing studies are used together; fieldwork in the study area is mainly based on traverses following rivers, which go through the BS. Landsat and radar images are carefully used to define related lineaments and rock types. Specific band combinations and band ratios combinations such as 5/7, 5/1, 5/4*3/4 successively in red, green, blue are used to define structural features in the study area. Lineaments found in the remote sensing study are used to interpret the structural history of the B.S, together with the structural data collected from field concerning the shape and the geometry of rock bodies. A new geological map of the area is being produced and new interpretation of the tectonics of East Madagascar is emerging from our studies. And then, Geochronologic analyses are in progress to determine the age and origin of the B.S.