SUMMARY A thermal conductivity profile through the upper crustal column is an essential ingredient in any thermal modelling. Granitoid is one of the major constituents of the upper crust in the Archaean cratons. Although granitoids have a wide range in composition, yet data on their thermal conductivity at elevated temperatures are very limited. At present, a single value is commonly used to characterize the decrease in thermal conductivity with temperature for the upper crust. We are reporting thermal conductivity measured at 25 °C, 50 °C and thereafter at 50 °C intervals up to 300 °C on 34 granitoid samples of four compositionally different types. The samples are alkali granite, biotite granite, granodiorite and metasomatised granodiorite from one of the Archaean cratons of the Indian shield, known as Bundelkhand Craton. Before studying the samples at elevated temperatures, these have been studied for their physical, petrological and geochemical characteristics. By 300 °C, the thermal conductivity decreases on the average by 28–31 per cent for metasomatised granodiorite, alkali granite and biotite granite, and in stark contrast by 16 per cent for granodiorite. Expressing the thermal conductivity variation with temperature as λT = λRT (1 + bT)–1, two distinct temperature coefficient (b) values have been found, 1.1 × 10–3 to 2.2 × 10–3 K–1 for alkali feldspar granite to monzogranite and 0.4 × 10–3 to 1.2 × 10–3 K–1 for granodiorite to tonalite to quartz diorite. One of the implications of this outcome is illustrated by applying these two distinct temperature coefficients for the upper crust for a 1-D generic model with a surface heat flow and appropriate radiogenic heat production of the crustal column in arriving at crustal temperature–depth profiles. The temperature differences at the base of a 40-km crust vary as much as 90 °C. Further, the temperature coefficient can be expressed as b = 0.71 × λRT– 0.63 for the alkali feldspar granite to monzogranite, whereas b = 0.83 × λRT– 1.26 for the granodiorite to tonalite to quartz diorite, which will be useful in determining the temperature coefficient of various types of granitoid from thermal conductivity at room temperature (λRT).

中文翻译：

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高达 300 °C 的不同成分的花岗岩的热导率及其对地壳热模型的影响

小结 通过上地壳柱的热导率剖面是任何热建模的重要组成部分。花岗岩是太古代克拉通上地壳的主要成分之一。尽管花岗岩的成分范围很广，但关于它们在高温下的导热率的数据却非常有限。目前，通常使用单一值来表征上地壳热导率随温度的降低。我们报告了在 25°C、50°C 和此后以 50°C 的间隔测量到 300°C 的热导率，对四种成分不同类型的 34 个花岗岩样品进行测量。这些样品是来自印度地盾的太古代克拉通之一的碱金属花岗岩、黑云母花岗岩、花岗闪长岩和交代花岗闪长岩，称为本德尔坎德克拉通。在研究高温下的样品之前，已经对其物理、岩石学和地球化学特征进行了研究。到 300 °C 时，交代花岗闪长岩、碱金属花岗岩和黑云母花岗岩的热导率平均降低 28% 至 31%，而花岗闪长岩则形成鲜明对比的是 16%。将热导率随温度的变化表示为 λT = λRT (1 + bT)–1，发现了两个不同的温度系数 (b) 值，碱性长石花岗岩的 1.1 × 10-3 到 2.2 × 10-3 K-1 monzogranite 和 0.4 × 10-3 到 1.2 × 10-3 K-1 花岗闪长岩到 tonalite 到石英闪长岩。通过将上地壳的这两个不同的温度系数应用于具有表面热流和适当的地壳柱产生的地壳温度-深度剖面的一维通用模型，说明了这一结果的影响之一。40公里地壳底部的温差变化高达90°C。此外，对于碱长石花岗岩到二长花岗岩，温度系数可以表示为 b = 0.71 × λRT- 0.63，而对于花岗闪长岩到英云闪长岩到石英闪长岩，b = 0.83 × λRT- 1.26，这将有助于确定温度系数从室温下的热导率 (λRT) 分析各种类型的花岗岩。40公里地壳底部的温差变化高达90°C。此外，对于碱长石花岗岩到二长花岗岩，温度系数可以表示为 b = 0.71 × λRT- 0.63，而对于花岗闪长岩到英云闪长岩到石英闪长岩，b = 0.83 × λRT- 1.26，这将有助于确定温度系数从室温下的热导率 (λRT) 分析各种类型的花岗岩。40公里地壳底部的温差变化高达90°C。此外，对于碱长石花岗岩到二长花岗岩，温度系数可以表示为 b = 0.71 × λRT- 0.63，而对于花岗闪长岩到英云闪长岩到石英闪长岩，b = 0.83 × λRT- 1.26，这将有助于确定温度系数从室温下的热导率 (λRT) 分析各种类型的花岗岩。