MAGMA FLOW INFERRED FROM ANISOTROPY OF MAGNETIC-SUSCEPTIBILITY IN THECOASTAL PARANA-ETENDEKA IGNEOUS PROVINCE - EVIDENCE FOR RIFTING BEFORE FLOOD VOLCANISM

The Parana-Etendeka igneous province is one of the largest flood volca nic provinces in the world; peak magmatic activity at 132 Ma is believ ed to have occurred about 5 m.y. before the birth of south Atlantic se a floor and development of rift basins along the Brazilian coastal mar gin. Anisotropy of magnetic susceptibility (AMS) measurements on 283 s amples (28 flows and 3 sills) from the Etendeka igneous province of Na mibia and 180 samples (21 flows) from the Parana province in Brazil re veal remarkably consistent fabric orientations with maximum susceptibi lity (K1) axes subhorizontal and parallel to the rifted margin. The AM S results are most likely due to shape anisotropy reflecting magma now directions, suggesting that lava flows and intrusive conduits near th e eventual rifted margin were controlled by structures having topograp hic expression in existence at the time of peak flood volcanism. These results imply that rifting preceded flood volcanism, at least in the portion of the magmatic province within 100 km of the nascent Mid-Atla ntic Ridge.