The orthogonal supersegment of the ultraslow-spreading Southwest Indian Ridge at 16°–25°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°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°–25°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°–21°E), which lacks large ridge-axis offsets, is associated with unstable segmentation patterns.

16°～25°E 超慢速扩张的西南印度洋脊正交超段的特征是地幔位温沿轴显着变化。对多波束测深、重力和磁数据进行了详细分析，以研究其在岩浆供应和地壳吸积过程中的变化。结果揭示了岩浆供应的明显跨轴变化。具体而言，区域平均地壳厚度从 7 Ma 左右到现在有系统地减小，表明区域岩浆供应减少。共轭脊翼之间地壳结构在区域尺度上不对称，南翼扩张速度较快，地壳较薄，构造伸展程度较大。地幔熔融地球动力学模型表明，观测到的地壳轴向厚度和主要元素地球化学的变化可以用洋脊轴下方约 40°C 的地幔位温向东下降来充分解释。在这项工作中，提出了一个综合模型来解释岩浆供应和脊分割稳定性的轴向变化。大脊轴偏移的存在可能在控制熔体供应方面发挥重要作用。东段（21°-25°E）的几个大脊轴偏移导致东部脊段中心的岩浆供应沿轴持续聚焦，从而实现准稳定分段。相比之下，缺乏大脊轴偏移的西段（16°–21°E）与不稳定的分割模式有关。