Abstract It has long been recognized that the stable oxygen isotope 18O/16O ratios of chemical sediments show a systematic decrease with increasing age. This continuous, 3.8 Ga long secular trend has been attributed to 80 °C hot early Earth oceans, a ~15‰ lower 18O/16O ratio of Archean seawater, or diagenetic obliteration of the original isotope signal. We demonstrate that high-precision triple oxygen isotope measurements including the rare third stable oxygen isotope 17O on silica rocks (cherts) can be used to shed light on this major problem in geochemistry. Our triple oxygen isotope data do not support 80 °C hot oceans in the Archean. The data also exclude that the 18O/16O of seawater was much lower in the Archean. Also, a simple freshwater-origin of cherts is not supported by the new data. We discuss the effects of diagenetic alteration on the triple oxygen isotope compositions of cherts and show that the Archean and Proterozoic cherts could have equilibrated with fluids with higher 18O/16O than today's oceans. For the Archean cherts, the high 18O/16O fluids required to explain the observations could reflect the composition of ambient seawater or of modified hydrothermal fluids. Oceans with higher 18O/16O ratio would be expected for an Archean “water world” without large continents. High 18O/16O fluids, however, could also have formed locally by reactions between seawater and the oceanic crust. Our study shows that high-precision triple oxygen isotope data provide new understandings of processes deep in time.

中文翻译：

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随着时间的推移，燧石的三氧同位素

摘要 人们早就认识到，化学沉积物的稳定氧同位素18O/16O 比值随着年龄的增长呈现系统性下降。这种持续 3.8 Ga 长的长期趋势归因于 80 °C 的早期地球热海洋、太古代海水的 18O/16O 比率降低约 15‰，或原始同位素信号的成岩作用消失。我们证明，包括硅石（燧石）上罕见的第三稳定氧同位素 17O 在内的高精度三氧同位素测量可用于阐明地球化学中的这一主要问题。我们的三重氧同位素数据不支持太古代 80 °C 的热海洋。数据还排除了太古宙中海水的 18O/16O 低得多。此外，新数据不支持简单的淡水来源的燧石。我们讨论了成岩蚀变对燧石三氧同位素组成的影响，并表明太古代和元古代燧石可以与比今天的海洋具有更高 18O/16O 的流体平衡。对于太古代硅质岩，解释观测结果所需的高 18O/16O 流体可以反映周围海水或改性热液流体的成分。对于没有大大陆的太古代“水世界”，预计会有更高的 18O/16O 比率的海洋。然而，高 18O/16O 流体也可能是由海水和洋壳之间的反应在局部形成的。我们的研究表明，高精度三氧同位素数据提供了对时间深处过程的新理解。