The Argentine continental margin north of 48 degrees S: sedimentary successions, volcanic activity during breakup

New seismic data and geophysical results from the outer Argentine continent al margin and from seismic flow-line transects across the oceanic Argentine /Brazil and Cape/Angola Basins are presented. The results document that the Early Cretaceous South Atlantic continental breakup and initial sea-floor spreading were accompanied by large-scale, transient volcanism emplacing vo luminous extrusive constructions on the conjugate outer continental mar ins of the South Atlantic. On the Argentine margin we interpret three major te ctono-volcanic crustal units beneath a thick and tectonically undisturbed s edimentary succession of Cretaceous and Tertiary age: (1) Syn-rift basins a nd even pre-rift features are present on the outer shelf; (2) a deeply buri ed, 60-120 km wide and several thousand metres thick volcanic wedge occupie s most of the slope. The wedge is characterized by seaward-dipping reflecto rs and is associated with the distinct magnetic Anomaly G; (3) the seaward adjacent oceanic crust of Cretaceous age shows isochronous changes of the s eismic images along our flow-line transects, suggesting some form of episod icity of rich magma and poor to moderate magma supply at the pre-existing m id-ocean ridge of the South Atlantic during Cretaceous time. (C) 1999 Elsev ier Science Ltd. All rights reserved.