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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 >Direct evidence of late Archean to early Proterozoic anoxic atmosphere from a product of 2.5 Ga old weathering
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Direct evidence of late Archean to early Proterozoic anoxic atmosphere from a product of 2.5 Ga old weathering

机译：从2.5 Ga的旧风化产物可以得出太古宙晚期到元古代早期缺氧大气的直接证据

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摘要

Because Precambrian paleosols (ancient soils formed by weathering) are usually subjected to later alteration, the evidence gleaned from chemical studies has provided inconclusive evidence on the atmospheric O_2 evolution. In a 2.6-2.45 Ga paleosol developed on Archean granite near Pronto mine, Canada, we found that Ce-rich rhabdophane formed directly during weathering, replaced primary apatite, and has survived for about 2.5 Ga because of its low solubility and high resistance to heat. Our data show that La, Ce, and Nd behaved similarly in both rocks and rhabdophane, i.e., most Ce existed as Ce~(3+) in the weathering solution, unlike the younger weathering profiles where Ce~(3+) oxidizes and forms cerianite, CeO_2. The presence of rhabdophane with Ce~(3+) throughout the Pronto paleosol provides compelling evidence of an anoxic atmosphere 2.6-2.45 Ga ago. Because apatite is a common accessory mineral in granitic rocks, Ce content of the replaced rhabdophane can be a useful indicator for tracing O_2 evolution in the Precambrian.
机译：由于前寒武纪古土壤（由风化作用形成的古老土壤）通常会在以后发生变化，因此从化学研究中收集到的证据为大气中O_2的演化提供了不确定的证据。在加拿大Pronto矿附近的Archean花岗岩上开发的2.6-2.45 Ga古土壤中，我们发现，富Ce的横纹烷在风化过程中直接形成，代替了初级磷灰石，并且由于其低溶解度和高耐热性而能够存活约2.5 Ga。 。我们的数据表明，La，Ce和Nd在岩石和大黄石中的行为相似，即，大多数Ce在风化溶液中以Ce〜（3+）的形式存在，这与年轻的风化剖面中Ce〜（3+）的氧化和形成不同。陶粒，CeO_2。整个Pronto古土壤中均存在带有Ce〜（3+）的大黄烷，这为2.6-2.45 Ga以前的缺氧气氛提供了令人信服的证据。由于磷灰石是花岗岩岩石中常见的辅助矿物，因此，取代的大黄烷中的Ce含量可以作为追踪前寒武纪O_2演化的有用指标。

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