Le systeme volcanique fissural du pays Mahafaly (SW de Madagascar)

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Abstract
The Mahafaly plateau region of southwestern Madagascar is traversed by a remarkable swarm of almost 500 parallel dikes following a fracture system, of the same age, extending from the border of the Androy volcanic massif in the southeast to the Karroo formations of the Sakoa region in the northwest. The dikes range from rhyolitic to ultrabasic in composition. Their age can definitely be established as post-Karroo. Although a relationship with the Karroo dolerites of South Africa is suggested, the fissure system seems to be genetically related to the Androy volcanism, in which case the dikes would be upper Cretaceous, whereas the South African Karroo dolerites were related to Rhaetic-upper Liassic volcanism.

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