Thermal transport properties of major Archean rock types to high temperature and implications for cratonic geotherms
Thermal transport properties of major Archean rock types to high temperature and implications for cratonic geotherms
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DOI：
10.1016/j.precamres.2013.05.009
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发表时间：
2013-08
影响因子：
3.8
通讯作者：
J. Merriman;A. Whittington;A. Hofmeister;P. Nabelek;K. Benn
中科院分区：
文献类型：
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作者：
J. Merriman;A. Whittington;A. Hofmeister;P. Nabelek;K. Benn
太古代地体的热结构在一定程度上取决于其独特岩石类型的热传输特性。我们用激光闪光仪测定了一套14种绿岩、镁铁质麻粒岩和英云闪长岩-奥长花岗闪长岩(TTG)岩石在大气压下的热扩散率(D)，其温度高达1000°C，这与传统接触技术没有系统误差。在室温下，对于条状铁的形成，D值从∼3.8mm2s−1到∼0.8mm2s−1，对于贫石英的奥长石来说。对于所有样品，热扩散率随着温度的升高而降低，因此该套岩石的D在∼700C时在−0.7m±0.1mm2s∼1附近收敛。将这些结果与根据模式矿物学计算的测量密度和热容相结合，提供了每一套岩石的热导率作为温度的函数。根据岩石类型的不同，近地表热导率在2.7W/m−1K−1之间变化，而下地壳的热导率为∼2W/m−1K−1，并且仅弱依赖于岩性，岩性比最上地幔(∼3.5W/m−1K−1)具有更强的热阻。在数值模型中使用随温度变化的热输运特性表明，地表地热对地壳热产生相对不敏感，因为高产热TTg岩石通常在低温下具有高的热扩散率和导电性，因此是它们产生的热的更有效的导体。这一发现意味着，根据地表钻孔测量计算地壳产热量可能会带来很大的不确定性。
The thermal structure of Archean terranes depends in part on the thermal transport properties of their distinctive rock types. We determined thermal diffusivity (D) of a suite of 14 greenstone, mafic granulite and tonalite–trondhjemite–granodiorite (TTG) rocks at temperatures up to 1000 °C at atmospheric pressure using laser flash analysis, which lacks systematic errors associated with conventional contact techniques. At room temperature,Dranges from ∼3.8 mm2s−1for banded iron formation to ∼0.8 mm2s−1for a quartz-poor trondjhemite. For all samples thermal diffusivity decreases with increasing temperature, such thatDfor the suite converges around ∼0.7 ± 0.1 mm2s−1at ∼700 °C. Combining these results with measured density and heat capacity calculated from modal mineralogy provides thermal conductivity as a function of temperature for each rock suite. Whereas near-surface thermal conductivity varies from 2.7 to 4.2 W m−1K−1depending on rock type, thermal conductivity of the lower crust is ∼2 W m−1K−1and only weakly dependent on lithology, which is more thermally resistive than the uppermost mantle (∼3.5 W m−1K−1).Use of temperature-dependent thermal transport properties in numerical models reveals that surface geotherms can be relatively insensitive to crustal heat production, because high heat-producing TTG rocks typically have high thermal diffusivity and conductivity at low temperatures and, consequently, are more efficient conductors of the heat they produce. This finding implies that calculations of crustal heat production from surface borehole measurements may entail significant uncertainties.