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Recognising early Archaean mantle: a reappraisal

机译：认识早期的太古地幔：重新评估

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This paper examines 3.8 Ga peridotites from Greenland and Labrador to test claims that these samples are unmodified early Archaean mantle. Geochemical criteria were applied in which samples were compared to the mantle array in Mg/Si versus Al/Si (wt percent) space, their REE patterns were compared to those of different mantle types and their chromite compositions were compared to mantle chromite compositions as expressed by their cr# and fe#. Geochemical data were used from the previously published works of Friend et al. (2002) and Bennett et al. (2002). Only two samples, from the region south of Isua satisfied all criteria, indicating that the area south of the Isua Greenstone Belt in west Greenland is a suitable place to search for early Archaean mantle. This study also confirms the observation by Friend et al. (2002) that early Archaean mantle from south of Isua is of a different character from Archaean mantle from the subcontinental lithosphere. Calculations presented here show that some mantle fragments from south of Isua experienced a lower degree of melt extraction and were probably more oxidising than early Archaean mantle preserved in the subcontinental lithosphere. Elemental concentrations of Os in early Archaean mantle are lower than the new estimate for the primitive upper mantle of Becker et al. (2006). Peridotites from the Isua greenstone belt are not mantle, but have an affinity with the layered intrusions found south of Isua.
机译：本文研究了来自格陵兰和拉布拉多的3.8 Ga橄榄岩，以证明这些样品是未经修饰的早期古生界地幔。应用地球化学标准，其中将样品在Mg / Si与Al / Si（wt％）空间中与地幔阵列进行比较，将其REE模式与不同地幔类型的REE模式进行比较，并将其铬铁矿成分与表示的地幔铬铁矿成分进行比较通过他们的cr＃和fe＃。地球化学数据来自Friend等先前发表的著作。 （2002）和Bennett等。 （2002）。伊苏阿以南地区只有两个样本满足所有条件，这表明格陵兰西部伊苏阿绿岩带以南地区是寻找早期古生界地幔的合适场所。这项研究也证实了Friend等人的观察。 （2002年），伊苏阿以南的早期古生界地幔与次大陆岩石圈的古生界地幔具有不同的特征。此处给出的计算结果表明，伊苏阿以南的一些地幔碎片的熔体抽出程度较低，并且氧化程度可能比亚大陆岩石圈中保存的早期古生界地幔更强。古代古生界地幔中Os的元素浓度低于Becker等人原始上地幔的新估计。 （2006）。伊苏阿绿岩带的橄榄岩没有地幔，但与伊苏阿南部发现的层状侵入体具有亲和力。

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