A Neoproterozoic Dextral Shear Zone, Central Madagascar

The origin of the Angavo Shear Zone (ASZ), a mega-scale ductile shear zone cutting the Precambrian basement of Madagascar is unknown, but of utmost importance for understanding the geometry and kinematics of the amalgamation of Gondwana supercontinent. Structure, field relationships, geochemistry and U-Pb zircon geochronology (LA-MC-ICP-MS and ID-TIMS) provide insights into the tectonic setting and geodynamic evolution of the ASZ. The N-S trending ASZ is characterized by oblique-right lateral displacement in conjunction with west over east thrusting. The Angavo belt records a polyphase evolution with magmatic activity taking place in at least three events: ~ 2.5 Ga, 730-825 Ma, and 550 Ma. The NeoArchean (~2.5 Ga) event is not yet characterized, whereas the 730-825 Ma continental arc magmatic events supports the idea of Neoproterozoic subduction beneath the Antananarivo block during the break-up of Rodinia prior the amalgamation of Gondwana. The late metamorphic events (ca. 550 Ma) are consistent with the timing of deformation of the ASZ, from which syn-tectonic granite yielded an age of 549±7.6 Ma. Based on structural analysis and U-Pb geochronology, the ASZ was probably connected to the Indian Achankovile shear zone located in southern Indian. In contrast, its African continuation is still unclear.