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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 >Identification of chemical sedimentary protoliths using iron isotopes in the > 3750 Ma Nuvvuagittuq supracrustal belt, Canada
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Identification of chemical sedimentary protoliths using iron isotopes in the > 3750 Ma Nuvvuagittuq supracrustal belt, Canada

机译：在加拿大> 3750 Ma Nuvvuagittuq上壳带中利用铁同位素鉴定化学沉积原生质

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An Eoarchean supracrustal belt dated at ca. 3750 Ma was recently identified in the Innuksuac Complex, northern Quebec (Canada). Rocks from the Nuvvuagittuq locality include mafic and ultramafic amphibolites, quartz-biotite and pelitic schists, orthogneisses, and banded quartz-magnetite-amphibole/pyroxene rocks of probable chemical sedimentary origin. The purported metasediments are enriched in the heavy isotopes of Fe by approximately 0.3 parts per thousand/amu relative to IRMM-014. They also have high Fe/Ti ratios, up to 100x that of associated amphibolite units. These signatures demonstrate that quartz-magnetite-amphibote/pyroxene rocks from Nuvvuagittuq are chemical sediments (e.g. banded iron-formations, BIFs) formed by precipitation of dissolved ferrous iron in a marine setting. All units were metamorphosed to upper amphibolite facies, which partly homogenized Fe isotopes. Variable Fe isotope compositions of bulk quartz-magnetite rocks are interpreted to reflect binary mixing between primary oxides and carbonates. Mixing relationships with major element chemistry (Ca/Fe, Mg/Fe, and Mn/Fe) are used to estimate the Fe isotope composition of the primary Fe-oxide phase (0.3 to 0.4 parts per thousand/amu) and the chemistry of the carbonate (siderite and ankerite). Iron isotopes can thus be used to constrain the primary mineralogy of Fe-rich chemical sedimentary precipitates before metamorphism. The possible presence of siderite in the primary mineral assemblage supports deposition under high PCO2. We developed an isotope distillation model that includes two possible abiotic oxidation paths, homogeneous and heterogeneous. The isotopic composition of Fe in the precursor phase of magnetite in BIFs can be explained by partial oxidation through oxygenic or anoxygenic photosynthesis of Fe from a hydrothermal source. (c) 2006 Elsevier B.V. All rights reserved.
机译：一条始于约2世纪的Eoarchean上地壳带。最近在魁北克北部（加拿大）的因努克苏克综合体中发现了3750 Ma。来自Nuvvuagittuq地区的岩石包括镁铁质和超镁铁质的角闪石，石英黑云母和片岩片岩，正片麻岩以及可能化学沉积成因的带状石英磁铁矿-闪石/辉石。相对于IRMM-014，据称的准沉积物富含Fe的重同位素，含量约为0.3 / 1000 / amu。它们还具有高的Fe / Ti比，是相关的角闪石单元的100倍。这些特征表明，Nuvvuagittuq的石英-磁铁矿-斜闪石/辉石岩是通过海洋环境中溶解的二价铁沉淀而形成的化学沉积物（例如带状铁形成的BIF）。所有单元都变质为上层闪石相，部分均质了Fe同位素。散装石英-磁铁矿岩石的可变铁同位素组成被解释为反映了初级氧化物和碳酸盐之间的二元混合。使用与主要元素化学成分（Ca / Fe，Mg / Fe和Mn / Fe）的混合关系来估算主要Fe-氧化物相的Fe同位素组成（0.3至0.4千分之千/ amu）和该元素的化学成分碳酸盐（菱铁矿和铁矿石）。因此，铁同位素可用于在变质之前限制富铁化学沉积沉淀的主要矿物学。主要矿物组合中可能存在菱铁矿，这有助于在高PCO2下沉积。我们开发了一种同位素蒸馏模型，该模型包括两种可能的非生物氧化途径，均相和异相。 BIF中磁铁矿前体相中Fe的同位素组成可以通过水热源中Fe的氧合或氧合光合作用进行部分氧化来解释。 （c）2006 Elsevier B.V.保留所有权利。

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