Variations in melt supply along an orthogonal supersegment of the Southwest Indian Ridge (16 degrees-25 degrees E)

The orthogonal supersegment of the ultraslow-spreading Southwest Indian Ridge at 16 degrees-25 degrees E is characterized by significant along-axis variations of mantle potential temperature. A detailed analysis of multibeam bathymetry, gravity, and magnetic data were performed to investigate its variations in magma supply and crustal accretion process. The results revealed distinct across-axis variations of magma supply. Specifically, the regionally averaged crustal thickness reduced systematically from around 7 Ma to the present, indicating a regionally decreasing magma supply. The crustal structure is asymmetric in regional scale between the conjugate ridge flanks, with the faster-spreading southern flank showing thinner crust and greater degree of tectonic extension. Geodynamic models of mantle melting suggested that the observed variations in axial crustal thickness and major element geochemistry can be adequately explained by an eastward decrease in mantle potential temperature of about 40 degrees C beneath the ridge axis. In this work, a synthesized model was proposed to explain the axial variations of magma supply and ridge segmentation stabilities. The existence of large ridge-axis offsets may play important roles in controlling melt supply. Several large ridge-axis offsets in the eastern section (21 degrees-25 degrees E) caused sustained along-axis focusing of magma supply at the centers of eastern ridge segments, enabling quasi-stable segmentation. In contrast, the western section (16 degrees-21 degrees E), which lacks large ridge-axis offsets, is associated with unstable segmentation patterns.