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首页> 外文期刊>Contributions to Mineralogy and Petrology >Ancient melt depletion overprinted by young carbonatitic metasomatism in the New Zealand lithospheric mantle
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Ancient melt depletion overprinted by young carbonatitic metasomatism in the New Zealand lithospheric mantle

机译：新西兰岩石圈地幔中年轻的碳酸盐岩交代作用覆盖的古代熔体耗竭

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摘要

Spinel facies dunite, harzburgite, Iherzolite and wehrlite mantle xenoliths from a cluster of Miocene volcanoes in southern New Zealand preserve evidence of the complex evolution of the underlying continental mantle lithosphere. Spinel Cr# records melt extraction with some values indicative of near complete removal of clinopy-roxene. LREE-enriched, low Ti/Eu and low Al_2O_3 clino-pyroxene and rare F-, LREE-rich apatite indicates subsequent interaction between peridotite and a metaso-matising carbonatitic melt. The clearest metasomatic signature occurs in the formerly highly depleted samples because there was little or no pre-existing clinopyroxene to dilute the carbonatite signature. For the same reason, the isotopic character of the metasomatising agent is best observed in the formerly highly depleted perido-tites (~(87)Sr/~(86)Sr = 0.7028-0.7031; ~(143)Nd/~(144)Nd = 0.5129; ~(206)Pb~~(204)Pb=20.2-20.3). These isotope ratios are very close to, but slightly less radiogenic than, the HIMU end-member mantle reservoir. Nd isotope data imply carbonatite metasomatism occurred within the last several hundred million years, with ubiquitous pyroxene core-to-rim Al diffusion zoning indicating that it must pre-date cooling of the lithospheric mantle following Late Cretaceous-Eocene rifting of Zealandia from Gondwana. Metasomatism was significantly younger than ancient Re-depletion ages of ~2 Ga and shows that decoupling of peridotite isotope systems has occurred.
机译：来自新西兰南部中新世火山群的尖晶石相辉长岩，辉长岩，Iherzolite和wehrlite地幔异岩保留了潜在的大陆地幔岩石圈复杂演化的证据。尖晶石Cr＃记录熔体萃取的一些值，表明几乎完全去除了斜柏木。富LREE的低Ti / Eu和低Al_2O_3斜向辉石以及稀有的F-，富LREE的磷灰石表明橄榄岩和变质交代的碳酸盐熔体之间随后发生相互作用。最清晰的交代特征发生在以前高度消耗的样品中，因为几乎没有或根本没有先生成的环吡咯酮可以稀释碳酸盐特征。出于同样的原因，变质作用剂的同位素特征最好在以前高度贫化的橄榄岩中观察到（〜（87）Sr /〜（86）Sr = 0.7028-0.7031;〜（143）Nd /〜（144） Nd ＝ 0.5129;〜（206）Pb ～～（204）Pb ＝ 20.2-20.3）。这些同位素比与HIMU端部成员地幔储层非常接近，但放射成因略小。 Nd同位素数据表明，碳酸盐岩交代作用发生在过去的几亿年内，辉石岩心到边缘的铝扩散带普遍存在，这表明它必须在冈瓦纳的白垩纪-始新世晚白垩世-始新世裂谷之后才对岩石圈地幔进行冷却。交代作用比古代的约2 Ga再耗尽年龄年轻得多，这表明橄榄岩同位素系统已经发生了解耦。

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