TECTONIC FRAMEWORK OF THE PRECAMBRIAN OF MADAGASCAR AND ITS GONDWANA CONNECTIONS - A REVIEW AND REAPPRAISAL

The Precambrian of Madagascar is divided into two sectors by the north -west trending sinistral Ranotsara shear zone, which continues in the Mozambique belt, probably as the Surma shear zone, and in Southern Ind ia as the Achankovil shear zone. South of Ranotsara six north-south tr ending tectonic belts are recognized that consist largely of granulite and high amphibolite facies paragneisses, phlogopite diopsidites, con cordant granites and granulites. North of Ranotsara the central - nort hern segment is traversed by a north - trending axial 100 - 150 km wid e dextral shear zone of probable Pan-African age, which was metamorpho sed under granulite and high amphibolite facies conditions and which h as reworked older basement. This shear zone continues across southern India as the Palghat-Cauvery shear zone. Major stratiform basic-ultrab asic complexes occur in the axial zone and in the basement to the west . Well preserved low grade continental margin-type sediments (quartzit es, mica schists and stromatolitic marbles) of Kibaran age are present in western Madagascar. Two partly greenschist grade sedimentary group s lie unconformably on high grade basement in north-east Madagascar. I sotopic age data suggest the presence in Madagascar of Archaean, Early and Mid-Proterozoic crustal material that was extensively reworked in Pan-African times.