DEATH AND TRANSFIGURATION OF A TRIPLE JUNCTION IN THE SOUTH-ATLANTIC

Three major lithospheric plates-Antarctic, South American, and African -meet in the South Atlantic near Bouvet Island where the Mid-Atlantic Ridge (MAR), the Southwest Indian Ridge (SWIR), and the American Antar ctic Ridge converge toward a fast evolving triple junction. A major ma gmatic pulse has recently built a new, swollen segment of the SWIR (Sp iess Ridge) that is propagating toward the MAR at a rate of 4 to 5 cen timeters per year, disrupting a former ridge-ridge-ridge (RRR) triple junction. A new triple junction will be established about 70 kilometer s to the north when the propagating SWIR/Spiess segment will impact wi th the MAR, probably within the next 1 million years. The American Ant arctic Ridge will take advantage of the MAR/SWIR duel by capturing an approximately 70-kilometer stretch of MAR, whereas the Antarctic plate will increase its size.