The Macquarie Ridge Complex (MRC) on the Australia‐Pacific plate boundary south of New Zealand is an extinct mid‐ocean ridge that has experienced a complex tectonic history and produced highly heterogeneous mid‐ocean ridge basalts (MORBs). When and how seafloor spreading ceased along the proto‐Macquarie mid‐ocean ridge remain elusive, and it is unclear how the mantle source of MORBs is affected by the gradual cessation of seafloor spreading at mid‐ocean ridges. To constrain the tectonic evolution of the MRC, the mantle source variations for MORBs at dying mid‐ocean ridges, and the mechanisms of mantle enrichment and asthenospheric heterogeneities, we report 11 pyroxene, plagioclase, basaltic glass, groundmass, and sericite ⁴⁰Ar/³⁹Ar and one zircon U‐Pb ages for the MRC MORBs. Our data reveal that basalts from the MRC seamounts were erupted between 25.9 and 1.6 Ma and Macquarie Island at ∼10 Ma. Combined age and plate reconstruction results reveal that the cessation of seafloor spreading at the MRC generally propagated from south to north along the ridge. Basalts produced by the then dying Macquarie mid‐ocean ridge at different times on different seamounts/island show a large variation in isotopic compositions and there is no clear correlation between ages and isotopic ratios. The heterogeneity of mantle source for MORBs from the proto‐Macquarie mid‐ocean ridge suggests that the upper asthenospheric mantle is heterogeneous, and such heterogeneity becomes most obvious at dying mid‐ocean ridges where the degrees of partial melting are low and a large range of melt compositions are produced.

中文翻译：

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麦格理岭综合体（西南太平洋）海底扩散停止的时间及其对上地幔非均质性的影响

新西兰南部澳大利亚-太平洋板块边界的麦格理山脊复合体（MRC）是一个灭绝的中海脊，经历了复杂的构造历史，并产生了高度异质的中海脊玄武岩（MORB）。沿着麦加里原海洋中脊停止海底扩散的时间和方式仍然难以捉摸，目前尚不清楚MORBs的地幔来源如何受到中洋海脊逐渐停止海底扩散的影响。为了限制MRC的构造演化，中垂山脊MORB的地幔源变化以及地幔富集和软流圈非均质性的机制，我们报告了11种辉石，斜长石，玄武质玻璃，地质和绢云母⁴⁰ Ar / ³⁹MRC MORB的Ar和一个锆石U-Pb年龄。我们的数据显示，MRC海山的玄武岩在25.9至1.6 Ma之间和Macquarie岛于10 Ma爆发。年龄和板块重建的综合结果表明，在MRC处海底扩展的停止通常沿山脊从南向北传播。当时垂死的麦格理海洋中脊在不同的海山/岛屿上在不同时间产生的玄武岩，其同位素组成变化很大，并且年龄和同位素比率之间没有明显的相关性。麦格理原始海中脊MORBs的地幔源的异质性表明，软流圈上地幔是非均质的，