ABSTRACT The intraplate rocks of the Dunedin Volcanic Group (DVG) in New Zealand’s South Island erupted in two discrete areas between 25 and 21 Ma before becoming distributed over > 7,800 km2 until ∼9 Ma. Although most eruptive centres were of small volume and mainly vented alkaline basanite, the largest centre–the 16–11 Ma composite Dunedin Volcano–discharged basanite and basalt through to trachyte and phonolite. DVG components were mainly derived from mantle sources with 87Sr/86Sr = ∼0.7029, 143Nd/144Nd = ∼0.5129, 206Pb/204Pb = ∼20.0, 207Pb/204Pb = ∼15.65, 208Pb/204Pb = 39.5 and εHf = +3.5 to + 10.1 that extended to anomalously light δ26Mg (−0.47). Exceptions are some potassic basalts in NW of the field with elevated 207Pb/204Pb and more radiogenic Sr. The DVG Sr-Nd-Pb isotopes mostly overlap with metasomatised anhydrous mantle peridotite xenoliths but have less radiogenic Hf, meaning that equivalent anhydrous mantle rock-types cannot be the sole magma sources. Although there is debate regarding whether DVG was derived from the lithospheric or asthenospheric mantle, intermittent melting of a middle lithospheric mantle metasomatised by hydrous asthenosphere-derived melts could account for: (1) the widely distributed magmatism for ∼16 Myr during which time Otago lithosphere shifted NW ∼ 870 km over the asthenosphere; (2) the small chemical range of the least evolved magmas; (3) the Sr-Nd-Pb-Hf isotopic range; and (4) an absence of lower lithosphere mantle xenoliths. This process could account for other occurrences of isotopically restricted Zealandia alkaline intraplate volcanism.

中文翻译：

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但尼丁火山群和西兰蒂亚碱性板内火山作用的修正模型

摘要 新西兰南岛但尼丁火山群 (DVG) 的板内岩石在 25 到 21 Ma 之间的两个离散区域喷发，然后分布在 > 7,800 平方公里的范围内，直到约 9 Ma。虽然大多数喷发中心体积小，主要喷发碱性玄武岩，但最大的中心——16-11 Ma 复合但尼丁火山——喷出玄武岩和玄武岩，直至粗面岩和响长岩。DVG 成分主要来源于地幔源，87Sr/86Sr = ∼0.7029, 143Nd/144Nd = ∼0.5129, 206Pb/204Pb = ∼20.0, 207Pb/204Pb = ∼15.65, +4b. = 15.65, +4b./20P. = 0.5129.扩展到异常轻的 δ26Mg (-0.47)。例外是该领域西北的一些钾玄武岩具有升高的 207Pb/204Pb 和更多放射成因的 Sr。DVG Sr-Nd-Pb 同位素大多与交代的无水地幔橄榄岩包体重叠，但具有较少放射成因的 Hf，这意味着等效的无水地幔岩石类型不能成为唯一的岩浆来源。尽管关于 DVG 是源自岩石圈还是软流圈地幔存在争议，但由含水软流圈衍生的熔体交代的中间岩石圈地幔的间歇性熔化可以解释：(1) 约 16 Myr 的广泛分布的岩浆活动，在此期间奥塔哥岩石圈在软流圈上偏北约 870 公里；(2) 演化最少的岩浆化学范围小；(3) Sr-Nd-Pb-Hf同位素范围；(4) 没有岩石圈下部地幔捕虏体。这个过程可以解释同位素限制的西兰岛碱性板内火山作用的其他发生。