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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
Grindlay, NR, Madsen JA, Rommevaux-Jestin C, Sclater J.  1998.  A different pattern of ridge segmentation and mantle Bouguer gravity anomalies along the ultra-slow spreading Southwest Indian Ridge (15 degrees 30 ' E to 25 degrees E). Earth and Planetary Science Letters. 161:243-253.   10.1016/s0012-821x(98)00154-x   AbstractWebsite

The results of a recent bathymetric and geophysical investigation of a similar to 650 km-long portion of the very slowly opening (16 mm/yr full rate) Southwest Indian Ridge (SWIR) between 15 degrees 30'E and 25 degrees E are presented. Bathymetry and mantle Bouguer gravity anomalies (MBA), caused by variations in crustal thickness and/or crustal and upper mantle densities, show different characteristics from those observed at faster spreading centers like the Mid-Atlantic Ridge (MAR) (20-30 mm/yr full rate). With the exception of the Du Toit Transform, none of the ridge-axis discontinuities have offsets greater than 10 km and few of the discontinuities have clearly defined off-axis traces. The MBA patterns associated with individual segments are much more complex than the simple circular bull's eyes lows reported along the MAR. While the short wavelength ridge segment length is comparable to that of the MAR, there is little correlation with MBA amplitude and segment length and axial relief. Furthermore, an eastward propagating magma source and an similar to 84 km-long zone of oblique spreading appears to define a fundamental boundary along the SWIR between two 250-300 km-long sections characterized by distinctly different axial morphology and gravity signatures. We interpret these results to indicate a long-wavelength segmentation pattern of the underlying upwelling mantle. Melt separates from the upwelling mantle at the base of the lithosphere and is channeled to the surface along dikes. Fissure eruptions within the rift valley build linear ridges defining a short-wavelength spatial pattern of ridge segmentation that is not directly related to the segmentation pattern of the upwelling mantle. Our results and interpretation are quite different than that predicted by extending current models of the faster spreading MAR to these ultra-slow spreading rates. (C) 1998 Elsevier Science B.V. All rights reserved.