The Bouvet Triple Junction.

摘要

The boundaries of three plates, South America, Africa, and Antarctica, Meet in a triple junction 250 km west of Bouvet Island. In the vicinity of the triple junction the most striking features of the Antarctica/South America and Africa/Antarctica plate boundaries are the Conrad and Bouvet fracture zones which trend N85 deg E and N45 deg E, respectively. By matching synthetic and observed magnetic anomaly profiles, it is shown that the Antarctica/South America, Africa/Antarctica, and Africa/South America plates are moving apart at half rates of 0.90 + or - 0.1, 0.83 + or - 0.1, and 1.60 + or - 0.1 cm/yr, respectively. The rates and directions of motions for the Antarctica/South America and Africa/Antarctica plates are significantly different from those predicted by analysis of plate motions assuming global closure. The three plate boundaries meet within 10 km of 54 deg 50's, 00 deg 40'W in a ridge-fault-fault (RFF) configuration. Within experimental error the relative velocity triangle closes. The triangle is isosceles, and the junction is stable. From the magnetic and topographic data the writers speculate that for the past 20m.y. the triple junction has been located close to the junction of the Bouvet and Conrad fracture zones and has had a predominantly RFF configuration.