SUMMARY Evaporites occur in various geological environments: sedimentary basins, orogenic belts, where they often act as tectonic decoupling layers, and as top-seals in hydrocarbon fields. In all cases, they affect the temperature distribution in the upper crust, as their thermal conductivity is relatively higher with respect to other sedimentary rocks. High heat conduction through evaporites enhances the geothermal gradient above the evaporitic layer and decreases it below, with potential consequences for surface heat flow, depth of the brittle–ductile transition and low-enthalpy geothermal exploitation. An accurate determination of their thermal conductivity is therefore necessary. We estimate the thermal conductivity of evaporitic rocks with a two-pronged method. First, an exhaustive review of the literature allows the determination of the conductivity for the main evaporitic minerals and of their variation with temperature. Secondly, in order to assess the effects of compositional variability, we select six samples of Triassic evaporites from the Apennines (from both outcrops and boreholes) and measure their mineralogical composition and thermal conductivity. The composition has a strong effect on conductivity, which goes from 5 W m–1 K–1 when anhydrite or dolomite are volumetrically predominant, to 2 W m–1 K–1 when gypsum is predominant. We also use various mixing models (where the rock conductivity is estimated from the mineralogical composition) and find sufficient agreement between measured and predicted values to justify the use of such models when direct measurements are not available. Finally, as an illustrative example of the thermal consequences of evaporites in the upper crust, we model the variations of temperature and surface heat flow caused by the occurrence of evaporitic layers of different thickness. The results show that the effects on crustal geotherms and the distribution of seismicity can be significant.

中文翻译：

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三叠纪蒸发岩的热导率

小结 蒸发岩存在于各种地质环境中：沉积盆地、造山带，它们通常在这些环境中充当构造脱钩层，并在油气田中充当顶盖。在所有情况下，它们都会影响上地壳的温度分布，因为它们的热导率相对于其他沉积岩更高。通过蒸发岩的高热传导增强了蒸发层上方的地温梯度并降低了蒸发层下方的地温梯度，对地表热流、脆韧转变深度和低焓地热开采具有潜在影响。因此，需要准确测定它们的热导率。我们用两管齐下的方法估计蒸发岩的热导率。第一的，对文献的详尽回顾可以确定主要蒸发矿物的电导率及其随温度的变化。其次，为了评估成分变化的影响，我们从亚平宁山脉（来自露头和钻孔）中选择了六个三叠纪蒸发岩样品，并测量了它们的矿物成分和热导率。该成分对电导率有很强的影响，当硬石膏或白云石体积占优势时，电导率从 5 W m-1 K-1 到石膏占优势时的 2 W m-1 K-1。我们还使用各种混合模型（其中岩石电导率是根据矿物成分估算的），并在测量值和预测值之间找到足够的一致性，以证明在无法进行直接测量时使用此类模型的合理性。最后，作为上地壳蒸发岩热影响的一个说明性示例，我们模拟了由不同厚度的蒸发层的出现引起的温度和地表热流变化。结果表明，对地壳地热和地震活动分布的影响可能是显着的。