The geochemistry and petrogenesis of Carnley Volcano, Auckland Islands, SW Pacific

Intraplate volcanism across Zealandia, South Eastern Australia, the Ross Sea Embayment and Marie Byrd Land in Antarctica define a magmatic province characterised by basalts with elevated 206Pb/204Pb (18.9–22.5), 87Sr/86Sr = ∼0.7035, Light Rare Earth enrichment [(Ce/Yb)n > 10], and convex-up mantle normalised incompatible multi-element patterns, peaking at Nb-Ta, with negative K and Pb anomalies. Trace element abundances and ratios (e.g. Zr/Nb, Y/Zr) resemble Ocean Island Basalts (OIB), distinct from Mid-Ocean Ridge Basalt (MORB), suggesting derivation from OIB-like reservoirs. Our preferred scenario envisages partial melting across the garnet-spinel stability fields involving asthenospheric and lithospheric mantle components. Melts accumulate in a column where the deep (asthenospheric) source is PM and the shallower source a melange of PM and subcontinental lithospheric mantle (DMM+1) enriched by carbonatite. Evolution of primary and near-primary magmas is controlled by olivine + clinopyroxene fractionation. Trachybasalts, trachytes and rhyolites show isotopic evidence for interaction with continental crust.西兰蒂亚、澳大利亚东南部、罗斯海海湾以及南极玛丽·伯德地的板内火山作用，共同构成了一个以特定玄武岩为特征的岩浆省：该类玄武岩具有升高的²⁰⁶Pb/²⁰⁴Pb比值（18.9–22.5）、⁸⁷Sr/⁸⁶Sr≈0.7035、轻稀土富集[(Ce/Yb)ₙ>10]，且呈现凸形的地幔标准化不相容多元素配分模式，在铌-钽（Nb-Ta）处达到峰值，同时显示钾（K）与铅（Pb）负异常。其微量元素丰度与比值（如Zr/Nb、Y/Zr）与洋岛玄武岩（Ocean Island Basalts，OIB）相似，而区别于洋中脊玄武岩（Mid-Ocean Ridge Basalt，MORB），表明其源区为类洋岛玄武岩源区。本研究优选的成因模型认为，岩浆形成于石榴子石-尖晶石稳定域内的部分熔融过程，涉及软流圈与岩石圈地幔端元。熔体在柱状岩浆房内聚集：深部（软流圈）源区为原始地幔（PM），浅部源区则是经碳酸岩交代富集的原始地幔（PM）与大陆下岩石圈地幔（DMM+1）的混杂体。原生及近原生岩浆的演化受橄榄石+单斜辉石分离结晶作用控制。粗面玄武岩、粗面岩与流纹岩则显示出与大陆地壳发生物质相互作用的同位素证据。