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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Picrite evidence for more Fe in Archean mantle reservoirs
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Picrite evidence for more Fe in Archean mantle reservoirs

机译：太古宙地幔储层中铁含量更高的微粉矿证据

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Recently discovered Archean amphibolites at the Lake of the Enemy, N.T., Canada, have alkaline ferropicrite compositions (MgO approx 14 wt%) with fractionated REE profiles (La/Yb = 10-15), high Nb/La ratios (1-2), and an average #epsilon#_(Nd) value of +1.1 at 2.66 Ga, suggestive of a mantle source that was slightly enriched relative to model 'MORB' reservoirs. The Fe-rich nature of these ferropicrites, together with other Archean ferropicrites and komatiites, indicates that the Archean equivalents of 'OIB' primitive magmas were up to 30% richer in Fe than today. The similar Mg content of Phanerozoic alkaline picrites argues against higher mantle potential temperatures being responsible for the higher Fe content of the Lake of the Enemy ferropicrites, and low alkalis do not support an explanation involving the effects of alkalis or oxidation state on Fe-Mg partitioning. The simplest explanation is that the mantle sources of some Archean hotspot magmas had more Fe than those of modern equivalents. The relatively Fe-rich character of Archean komatiitic lavas, on the other hand, may reflect higher temperatures, and thus depths of initiation of melting, in the Archean. This interpretation requires, however, an absence of low-pressure (< 3.0 GPa) primary melts in the Archean. Alternatively, the Fe-rich character of komatiitic magmas may also reflect Archean mantle sources that contained more Fe than pyrolite models (Mg# approx 0.89). Proterozoic picritic lavas resemble their Archean equivalents, while most Mesozoic picritic lavas are indistinguishable from those of today. These data indicate that the Fe content of the Earth's mantle may have decreased over time, and requires either a sink for Fe in the core or the isolation of Fe-rich material in the lower mantle.
机译：最近在加拿大新罕布什尔州的敌人湖发现的太古代角闪石具有碱性铁锰矿成分（MgO约为14 wt％），具有分馏的REE分布（La / Yb = 10-15），高Nb / La比（1-2） ，并且在2.66 Ga时平均#epsilon #_（Nd）值为+1.1，表明地幔源相对于模型“ MORB”储层略有富集。这些铁锰铁矿以及其他太古代铁锰矿和高锰铁矿中富含铁的性质表明，“ OIB”原始岩浆的太古代等效物比今天的铁含量高出30％。相似的镁镁盐含量的古生代碱性苦杏仁粉反对较高的地幔势能造成敌人铁肥性苦粉岩中较高的铁含量，而低碱度不支持涉及碱金属或氧化态对铁镁盐分配的影响的解释。 。最简单的解释是，一些太古代热点岩浆的地幔源中的铁比现代等价岩中的铁更多。另一方面，太古宙科迈特熔岩的铁含量相对较高，这可能反映了太古宙的较高温度，进而反映了融化的起始深度。但是，这种解释要求在太古代没有低压（<3.0 GPa）初级熔体。另外，科马特岩浆岩的富铁特征也可能反映了比起辉石岩模型（Mg＃约0.89）含有更多铁的太古宙幔源。古生代的火山岩熔岩类似于它们的太古代的熔岩，而大多数中生代的火山岩熔岩与今天的熔岩没有区别。这些数据表明，地幔中的铁含量可能会随着时间的推移而下降，并且需要在地核中吸收铁或在下地幔中分离富铁物质。

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