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首页> 外文期刊>Precambrian Research >Unusual, basin-scale, fluid-rock interaction in the Palaeoproterozoic Onega basin from Fennoscandia: Preservation in calcite delta O-18 of an ancient high geothermal gradient
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Unusual, basin-scale, fluid-rock interaction in the Palaeoproterozoic Onega basin from Fennoscandia: Preservation in calcite delta O-18 of an ancient high geothermal gradient

机译：芬诺斯堪迪亚的古元古代奥涅加盆地异常，盆地尺度的流体-岩石相互作用：保存在古代高地热梯度的O-18方解石三角洲中

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摘要

A variety of carbonates of different geneses, as indicated by petrography and geochemistry, are found throughout 400 m of the volcano-sedimentary rocks of the Zaonega Formation of Palaeoproterozoic age in the Onega basin of Fennoscandia. Following intensive sampling and analysis of varied calcites from drillcore recovered during the ICDP FAR-DEEP program, we report a highly unusual depth distribution of calcite oxygen isotope values (delta O-18(cal)). Unprecedentedly for such rocks, the delta O-18(cal) values over the full depth interval of 400 mare strongly linearly correlated with depth (r(2) = 0.9015, n = 178). We propose that this is the result of major oxygen isotope resetting through water-rock interaction with a fluid of relatively constant oxygen isotopic composition (delta O-18(w)). In this model, the observed linear delta O-18(cal)-depth relationship is then a consequence of the increase in temperature with depth because of the background geothermal gradient. Minor deviations from the overall linear trend are likely due to bed-scale geological factors including locally high impermeability, and oxygen isotope modification of delta O-18(w) by comparatively intense water-rock interaction.
机译：岩石学和地球化学表明，在Fennoscandia的Onega盆地古元古代的Zaonega组的火山沉积岩的整个400 m中发现了各种不同成因的碳酸盐。在对ICDP FAR-DEEP计划期间从钻芯中提取的方解石进行深入采样和分析之后，我们报告了方解石氧同位素值（δO-18（cal））的深度分布非常不寻常。对于此类岩石，史无前例的是，在400个母马的整个深度范围内，δO-18（cal）值与深度高度线性相关（r（2）= 0.9015，n = 178）。我们认为这是通过水岩与氧同位素组成相对恒定的流体（δO-18（w））相互作用而使主要氧同位素复位的结果。在该模型中，观测到的线性δO-18（cal）-深度关系是背景地热梯度导致温度随深度增加的结果。与整体线性趋势的微小偏差可能是由于床尺度的地质因素（包括局部高抗渗性）和三角洲O-18（w）的氧同位素通过相对强烈的水-岩相互作用而引起的。

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