Epidote is a potential water carrier in subducting oceanic crust, and it is involved in temperature records from blueschist and eclogite exhumed from subduction zones. Thermal conductivity (κ) and thermal diffusivity (D) of epidote were measured at 303–1,473 K and 0.5–3.0 GPa using the transient plane-source method. κ and D values decreased with temperature before dehydration, but increase anomalously with temperature after dehydration, and finally decreased with crystallization of the decomposition products. Thermal conductivity and thermal diffusivity of epidote exhibited a positive pressure dependence. The obtained κ and D values of epidote were significantly smaller than those of nominally anhydrous minerals and other hydrous minerals. X-ray computed tomography analysis revealed that the pores inside the recovered samples were partially connected. κ and D values were dominated by conductive heat transport before dehydration, while the anomalous increase in the thermal parameters after dehydration may have been caused by the fluid inside the connected pores. Using variable thermal conductivity obtained in this study, the thermal structures of warm subducting slabs associated with epidote-blueschist and epidote-eclogite facies were modeled. Our estimations revealed that the temperatures of warm slabs below the forearc with the epidote-blueschist and epidote-eclogite facies may be lower 7–10 and ∼40–50 K compared to those determined using a constant thermal conductivity value. This implies that the presence of epidote-blueschist and epidote-eclogite could reduce the temperature of the slab, which may alter the dehydration depth of the slab.

中文翻译：

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绿帘石的低导热性及其对海洋地壳的冷却作用


绿帘石是俯冲海洋地壳的潜在水载体，它与从俯冲带挖掘的蓝片岩和榴辉岩的温度记录有关。使用瞬态平面源法在 303–1,473 K 和 0.5–3.0 GPa 下测量绿帘石的热导率 （κ） 和热扩散率 （D）。脱水前κ和D值随温度升高，脱水后随温度异常升高，最后随着分解产物的结晶而降低。绿帘石的热导率和热扩散率表现出正压依赖性。获得的绿帘石的 κ 和 D 值显著小于标称无水矿物和其他含水矿物。X 射线计算机断层扫描分析显示，回收样品内部的孔隙部分相连。κ 和 D 值以脱水前的传导热传递为主，而脱水后热参数的异常增加可能是由连接孔内的流体引起的。利用本研究中获得的可变热导率，对与绿帘石-蓝片岩和绿帘石-榴辉岩相相关的暖俯冲板块的热结构进行了建模。我们的估计表明，与使用恒定热导率值确定的温度相比，具有绿帘石-蓝片岩和绿帘石-榴辉岩相的前弧以下暖板的温度可能低于 7-10 和 ∼40-50 K。这意味着绿帘石-蓝片岩和绿帘石-榴辉岩的存在可以降低板坯的温度，这可能会改变板坯的脱水深度。