Structure and metamorphism of the granitic basement around Antananarivo: A key to the Pan‐African history of central Madagascar and its Gondwana connections

The Precambrian basement of Madagascar acquired a polyphase imprint during the Pan‐African orogeny. In northern central Madagascar, emplacement of stratoid alkaline granites at midcrustal depth (4–5 kbars) led to formation of a layered crust in a postcollisional extensional regime at 630 Ma (D1). Subsequently, the structures of the stratoid granites were rotated by the sinistral and transpressive E‐W Antananarivo flexure (or virgation) zone (D2). East of Antananarivo the structures of the D1 layered crust and the D2 virgation are crosscut by the steeply dipping N‐S foliations of the Angavo belt. Lineations gently plunging to the north attest that the Angavo belt is a major strike‐slip shear zone that formed under low‐pressure granulitic conditions (3 kbars, 790°C). The nearby porphyritic Carion granite was emplaced at the end of this period of N‐S shearing (D3), which can thus be no younger than 530 Ma. Late‐Pan‐African (580–550 Ma) strike‐slip motion along broadly N‐S shear zones has been recognized elsewhere in Madagascar and in its Gondwana connections. Continuation of the Angavo belt as one of the high strain belts of the Arabian‐Nubian Shield is discussed in the general framework of Gondwana assembly.