The Australian-Antarctic Ridge (AAR) is an intermediate-spreading rate system located between the Southeast Indian Ridge and Macquarie Triple Junction of the Australian-Antarctic-Pacific plates. KR1 is the easternmost and longest AAR segment and exhibits unique axial morphology and various volcanic structures. We identified three asymmetric seamount chains positioned parallel to the seafloor spreading direction, which were indicative of prevalent off-axis volcanism in the vicinity of segment KR1. Two-dimensional magnetic modeling was used to predict the magnetization polarity of the seamounts, as well as to constrain their formation time and duration. The magnetic modeling revealed that the majority of the examined seamounts were formed over a period of less than ∼600 kyrs. The seamount formation primarily occurred during two distinct volcanic pulses from 0.16–1.14 to 1.58–2.69 Ma. A temporal gap of 200–650 kyrs between the formation time of the seamounts and seafloor was estimated for certain seamounts that were formed much later than their underlying seafloor and at a distance of 10–20 km from the KR1 axis. Typically, such off-axis seamount activity is related to axial mantle convection caused by excessive magma supply near the ridge crest. Considering the scale of off-axis volcanism and thickening lithosphere ∼20 km away from the axis with intermediate-spreading rates, small-scale upwelling made feasible by the fertile mantle heterogeneity is proposed as the mechanism for the seamount formations at off-axis distances, and the geochemically enriched compositions of the seamounts support this alternative explanation.

中文翻译：

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澳大利亚-南极海脊最东段离轴海山火山活动的磁约束

澳大利亚-南极海脊（AAR）是一个中等扩张速率系统，位于澳大利亚-南极-太平洋板块的东南印度海脊和麦格理三重交界之间。KR1 是最东、最长的 AAR 段，具有独特的轴向形态和各种火山结构。我们确定了三个与海底扩张方向平行的不对称海山链，这表明 KR1 段附近存在普遍的离轴火山活动。二维磁模型用于预测海山的磁化极性，并限制其形成时间和持续时间。磁性模型显示，大多数被检查的海山是在不到 600 kyrs 的时间内形成的。海山的形成主要发生在 0.16-1.14 至 1.58-2.69 Ma 的两个不同的火山脉冲期间。对于某些海山形成时间比其下伏海底晚得多且距离 KR1 轴 10-20 公里，估计海山和海底的形成时间之间存在 200-650 kyrs 的时间差距。通常，这种离轴海山活动与脊顶附近岩浆供应过多引起的轴向地幔对流有关。考虑到离轴火山活动的规模和离轴约 20 公里处的岩石圈增厚且具有中等扩张率，提出了由肥沃的地幔非均质性使小规模上升流成为可能的离轴距离海山地层的机制，