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Takeuchi, CS, Sclater JG, Grindlay NR, Madsen JA, Rommevaux-Jestin C.  2010.  Segment-scale and intrasegment lithospheric thickness and melt variations near the Andrew Bain megatransform fault and Marion hot spot: Southwest Indian Ridge, 25.5 degrees E-35 degrees E. Geochemistry Geophysics Geosystems. 11   10.1029/2010gc003054   AbstractWebsite

We analyze bathymetric, gravimetric, and magnetic data collected on cruise KN145L16 between 25.5 degrees E and 35 degrees E on the ultraslow spreading Southwest Indian Ridge, where the 750 km long Andrew Bain transform domain separates two accretionary segments to the northeast from a single segment to the southwest. Similar along-axis asymmetries in seafloor texture, rift valley curvature, magnetic anomaly amplitude, magnetization intensity, and mantle Bouguer anomaly (MBA) amplitude within all three segments suggest that a single mechanism may produce variable intrasegment lithospheric thickness and melt delivery. However, closer analysis reveals that a single mechanism is unlikely. In the northeast, MBA lows, shallow axial depths, and large abyssal hills indicate that the Marion hot spot enhances the melt supply to the segments. We argue that along-axis asthenospheric flow from the hot spot, dammed by major transform faults, produces the inferred asymmetries in lithospheric thickness and melt delivery. In the southwest, strong rift valley curvature and nonvolcanic seafloor near the Andrew Bain transform fault indicate very thick subaxial lithosphere at the end of the single segment. We suggest that cold lithosphere adjacent to the eastern end of the ridge axis cools and thickens the subaxial lithosphere, suppresses melt production, and focuses melt to the west. This limits the amount of melt emplaced at shallow levels near the transform fault. Our analysis suggests that the Andrew Bain divides a high melt supply region to the northeast from an intermediate to low melt supply region to the southwest. Thus, this transform fault represents not only a major topographic feature but also a major melt supply boundary on the Southwest Indian Ridge.

Peyve, AA, Skolotnev SG, Ligi M, Turko NN, Bonatti E, Kolodyazhnyi SY, Chamov NP, Tsukanov NV, Baramykov YE, Eskin AE, Grindlay N, Sclater JG, Brunelly D, Pertsev AN, Cipriani A, Bortoluzzi G, Mercuri R, Paganelli E, Muccini F, Takeuchi C, Zaffagnini F, Dobrolyubova KO.  2007.  Investigation of the Andrew Bain transform fault zone (African-Antarctic region). Doklady Earth Sciences. 416:991-994.   10.1134/S1028334X07070021   Abstract
Sclater, JG, Grindlay NR, Madsen JA, Rommevaux-Jestin C.  2005.  Tectonic interpretation of the Andrew Bain transform fault: Southwest Indian Ocean. Geochemistry Geophysics Geosystems. 6   10.1029/2005gc000951   AbstractWebsite

[1] Between 25 degrees E and 35 degrees 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 degrees 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 zone jumping successively northward created the en echelon ridges and valleys in the eastern central portion of the domain. The style of accretion changed to that of a transform relay zone, during a final northward jump, at 3.2 Ma.