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首页> 外文期刊>The American mineralogist >Clay minerals as geo-thermometer: A comparative study based on high spatial resolution analyses of illite and chlorite in Gulf Coast sandstones (Texas, U.S.A.)
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Clay minerals as geo-thermometer: A comparative study based on high spatial resolution analyses of illite and chlorite in Gulf Coast sandstones (Texas, U.S.A.)

机译：黏土矿物作为地热仪：一项基于墨西哥湾沿岸砂岩中伊利石和绿泥石的高空间分辨率分析的对比研究（美国德克萨斯州）

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摘要

Phyllosilicates are among the most important stable minerals within the Earth's crust. Their use as geo-thermometer bears great potential for application to the thermal history of rocks within the stability range of layered silicates and was tested here. A high-resolution analytical technique combining focused ion beam (FIB) milling and analytical electron microscopy (AEM) analysis has been applied to a series of sandstone core samples from the Gulf Coast (Texas, U.S.A.). The nanoscale compositional variations of K-deficient mica and chlorite flakes show that rim compositions are the most likely to approach equilibrium compositions, whereas core compositions may be relict, especially for illite-like phases. These rim analyses were used to test existing empirical or thermodynamically formulated thermo(baro)meters against maximum temperatures, which are perfectly constrained for the selected samples as they were measured in situ during drilling (100-230 °C and 300-1200 bars). The results show that most of the empirical models overestimate the temperature, while thermodynamic models yields reasonable estimates for diagenetic to anchizonal conditions, especially if the Fe3+ content is taken into account. This study clearly shows that phyllosilicates thermometry is reliable when combined with an analytical technique giving access to the fine-scale compositional variations that may represent local equilibration, whereas using micrometric compositional analysis precludes trustworthy application of such thermometers.
机译：苯硅酸盐是地壳内最重要的稳定矿物之一。它们用作地热仪具有巨大的潜力，可用于层状硅酸盐稳定范围内的岩石热历史，并在此处进行了测试。将聚焦离子束（FIB）铣削与分析电子显微镜（AEM）分析相结合的高分辨率分析技术已应用于来自墨西哥湾沿岸（美国德克萨斯州）的一系列砂岩岩心样品。缺钾云母和亚氯酸盐薄片的纳米级成分变化表明，轮辋成分最有可能接近平衡成分，而核成分可能残留，尤其是对于伊利石样相。这些边缘分析用于针对最高温度测试现有的由经验或热力学制定的温度计（气压计），因为在钻孔过程中对它们进行了现场测量（100-230°C和300-1200 bar），因此这些温度对选定的样品具有完美的约束。结果表明，大多数经验模型都高估了温度，而热力学模型则对成岩至chi附条件产生了合理的估计，特别是如果考虑了Fe3 +的含量。这项研究清楚地表明，与一种分析技术相结合时，页硅酸盐温度测量法是可靠的，该分析技术可以提供代表局部平衡的精细尺度组成变化，而使用微米级组成分析则无法可靠地使用此类温度计。

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