Tectonic interpretation of the Andrew Bain transform fault: Southwest Indian Ocean

• Published in: Geochemistry, Geophysics, Geosystems
• Main Authors: Sclater, John, G, Grindlay, Nancy, R, Madsen, John, A, Rommevaux-Jestin, Céline
• Other Authors: Scripps Institution of Oceanography (SIO - UC San Diego), University of California San Diego (UC San Diego), University of California (UC)-University of California (UC), University of North Carolina Wilmington (UNC), University of North Carolina System (UNC), University of Delaware Newark, Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2005
• Subjects: 3040 Marine Geology and Geophysics: Plate tectonics (8150; tectonics Index Terms: 3039 Marine Geology and Geophysics: Oceanic transform and fracture zone processes; 632 words; 8158); Components: 11; 8155; 3 tables Keywords: megatransform; 7 figures; 8157; [SDU]Sciences of the Universe [physics]; Bain; Indian; Antarc*; Antarctica
• Online Access: https://insu.hal.science/insu-01777716; https://insu.hal.science/insu-01777716/document; https://insu.hal.science/insu-01777716/file/Sclater_et_al-2005-Geochemistry,_Geophysics,_Geosystems.pdf; https://doi.org/10.1029/2005GC000951

International audience [1] Between 25°E and 35°E, a suite of four transform faults, Du Toit, Andrew Bain, Marion, and Prince Edward, offsets the Southwest Indian Ridge (SWIR) left laterally 1230 km. The Andrew Bain, the largest, has a length of 750 km and a maximum transform domain width of 120 km. We show that, currently, the Nubia/Somalia plate boundary intersects the SWIR east of the Prince Edward, placing the Andrew Bain on the Nubia/Antarctica plate boundary. However, the overall trend of its transform domain lies 10° clockwise of the predicted direction of motion for this boundary. We use four transform-parallel multibeam and magnetic anomaly profiles, together with relocated earthquakes and focal mechanism solutions, to characterize the morphology and tectonics of the Andrew Bain. Starting at the southwestern ridge-transform intersection, the relocated epicenters follow a 450-km-long, 20-km-wide, 6-km-deep western valley. They cross the transform domain within a series of deep overlapping basins bounded by steep inward dipping arcuate scarps. Eight strike-slip and three dip-slip focal mechanism solutions lie within these basins. The earthquakes can be traced to the northeastern ridge-transform intersection via a straight, 100-km-long, 10-km-wide, 4.5-km-deep eastern valley. A striking set of seismically inactive NE-SW trending en echelon ridges and valleys, lying to the south of the overlapping basins, dominates the eastern central section of the transform domain. We interpret the deep overlapping basins as two pull-apart features connected by a strike-slip basin that have created a relay zone similar to those observed on continental transforms. This transform relay zone connects three closely spaced overlapping transform faults in the southwest to a single transform fault in the northeast. The existence of the transform relay zone accounts for the difference between the observed and predicted trend of the Andrew Bain transform domain. We speculate that between 20 and 3.2 Ma, an oblique accretionary ...