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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Petrology and geochemistry of Marion and Prince Edward Islands, Southern Ocean: Magma chamber processes and source region characteristics
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Petrology and geochemistry of Marion and Prince Edward Islands, Southern Ocean: Magma chamber processes and source region characteristics

机译：南大洋马里恩群岛和爱德华王子岛的岩石学和地球化学：岩浆腔过程和源区特征

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摘要

New bulk rock geochemical data on an extensive suite of samples from the Marion and Prince Edward Islands, located in the Southern Ocean at ~37°45'E, 46°55'S, show highly coherent major and trace element variations. Rock types are dominated by alkali basalt, with lesser hawaiite and minor mugearite and benmoreite. Prince Edward Island has in addition rare trachytes exposed on the plateau, and xenoliths of comenditic rhyolite pumice were found in a basalt flow of the 1980 eruption on Marion Island. Lavas from Prince Edward Island differ from those erupted on Marion Island by having subtly distinct incompatible trace element ratios (e.g. Zr/Nb = 9.1 vs 6.7; Ba/Nb = 7.8 vs 6.7; Ce/Pb = 31 vs 36), and lower ~(87)Sr/~(86)Sr (0.70302) and higher ~(143)Nd/~(144)Nd (0.51300) isotope ratios than found on Marion Island (0.70336-0.70349; 0.51292-0.51295). The two islands are indistinguishable in terms of Pb isotope ratios (~(206)Pb/~(204)Pb = 18.61-18.75,~(207)Pb/~(204)Pb = 15.54-15.56). Quantitative modelling suggests that the range in rock types found on each island can be ascribed to extensive low pressure crystal fractionation of phenocryst phases. For example, hawaiite can be related to the more primitive alkali basalts by some 24% fractional crystallisation of olivine, clinopyroxene, plagioclase and minor FeTi-oxides, whereas the more evolved mugearites and benmoreites require, respectively a further 36% and 24% fractional crystallisation to account for their felsic compositions. The trachytes of Prince Edward Island appear to represent the residual 28% magma following extensive crustal fractionation of dominantly clinopyroxene, plagioclase and FeTi-oxide with minor apatite. None of the sampled lavas have compositions characteristic of true primary magmas, but the least evolved, with Mg# ~63, appear to have experienced as much as 18% olivine fractionation from a primary magma with ~15 wt% MgO. The rhyolite pumice is distinct in composition from Bouvet rhyolite or South Sandwich Island pumice and may belong to an earlier, submarine eruption at or near Marion Island. The enriched incompatible element ratios (Zr/Nb = 6-9; La/Yb_n = 10.6; Y/Nb = 0.73) and radiogenic ~(87)Sr/~(86)Sr and unradiogenic ~(143)Nd/~(144)Nd isotope ratios show that the lavas erupted on Marion and Prince Edward Islands resulted from melting an enriched mantle source, consistent with derivation from an upwelling deep mantle plume. Pb isotope ratios (Δ8/4Pb~33) confirm the absence of any DUPAL signature in the source region of these magmas.
机译：来自位于南洋〜37°45'E，46°55'S上的马里恩和爱德华王子岛的大量样本的新的散装岩石地球化学数据显示出高度连贯的主要和微量元素变化。岩石类型以碱性玄武岩为主，较少的夏威夷石，次要的钙铝石和膨润土。爱德华王子岛（Prince Edward Island）的高原上还稀有稀有的菱形长绒毛，在马里恩岛（Marion Island）1980年喷发的玄武岩流中发现了粉状流纹岩浮石的异岩。爱德华王子岛的拉瓦斯与马里恩岛上的拉瓦斯有所不同，其痕量元素比率微妙地不相容（例如Zr / Nb = 9.1 vs 6.7； Ba / Nb = 7.8 vs 6.7； Ce / Pb = 31 vs 36），并且更低〜 （87）Sr /〜（86）Sr（0.70302）和更高的〜（143）Nd /〜（144）Nd（0.51300）同位素比比在马里恩岛（0.70336-0.70349; 0.51292-0.51295）上发现的高。这两个岛在Pb同位素比率方面没有区别（〜（206）Pb /〜（204）Pb = 18.61-18.75，〜（207）Pb /〜（204）Pb = 15.54-15.56）。定量建模表明，在每个岛上发现的岩石类型范围可归因于表晶相的广泛低压晶体分级。例如，夏威夷石与橄榄石，斜辉石，斜长石和少量FeTi氧化物的约24％分级结晶可能与更原始的碱性玄武岩有关，而演化程度更高的硅钙石和膨润土则分别需要进一步的36％和24％分级结晶。来说明他们的长篇作品。爱德华王子岛的小行星似乎代表了残留的28％岩浆，这主要是由次要辉石，斜长石和氧化铁钛与少量的磷灰石进行了广泛的地壳分离。采样的熔岩中没有一个具有真正初生岩浆的成分特征，但演化最少的Mg＃〜63，似乎经历了来自初生岩浆的Mg＃〜15 wt％的橄榄石分级多达18％。流纹岩浮石在组成上不同于布韦特流纹岩或南桑威奇岛浮石，并且可能属于马里恩岛或其附近的海底喷发。富集的不相容元素比率（Zr / Nb = 6-9; La / Yb_n = 10.6; Y / Nb = 0.73）和放射源〜（87）Sr /〜（86）Sr和非放射源〜（143）Nd /〜（144 Nd同位素比值表明，马里恩（Marion）和爱德华王子岛（Edward Prince Islands）上喷发的熔岩是由于融化了丰富的地幔源而产生的，这与上升的深地幔羽流相一致。铅同位素比（Δ8/ 4Pb〜33）证实了这些岩浆的源区中没有任何DUPAL标记。

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