The current status of thermobarometry in metamorphic rocks
The current status of thermobarometry in metamorphic rocks
复制标题
DOI：
10.1144/gsl.sp.1989.043.01.02
复制
发表时间：
1989
期刊：
影响因子：
--
通讯作者：
E. Essene
中科院分区：
文献类型：
--
作者：
E. Essene
关于压力（P）和温度（T）的概要信息是变质岩地区研究的一个基本方面。不幸的是，许多研究人员使用的热压力计未经实验校准，对P - T变化不敏感或过于敏感，依赖于水压的先验假设（如大多数岩石成因格子），或者在冷却时会迅速重置。许多体系基于不准确的热力学数据，涉及结构状态特征不充分的固体，忽略热膨胀和压缩性的影响，或者需要在P - T - X空间进行长距离外推。例如，广泛使用的石榴石 - 单斜辉石KD温度计的应用可能需要外推到当前辉石和石榴石的热力学模型仍不确定的温度。用于黑云母 - 石榴石的Mg/Fe交换温度计的当前版本在许多应用中涉及大量的成分外推，并且黑云母在从较高温度冷却时很容易重置。最广泛使用的压力计基于钙铝榴石 + 蓝晶石 + 石英 = 钙长石这一反应的稀释，但如果不针对P - T - X校正摩尔体积，对于地壳变质岩的压力测定可能会产生1 - 2千巴的系统误差。鉴于在这些温度下石榴石和斜长石的a - X关系未知，目前将这种压力计应用于在T < 600 - 650°C达到平衡的岩石是不合理的。然而，通过精心选择，如果可以应用多种不同的平衡，在许多变质岩地区热压力测定可能精确到±50°C和±1千巴。对于T≥600 - 650°C有用的经过良好校准的压力计依赖于基于诸如铁铝榴石 + 金红石 = 钛铁矿 + 夕线石 + 石英、石榴石 + 石英 = 铁辉石 + 斜长石、石榴石 + 金红石 = 钛铁矿 + 钙长石 + 石英以及铁铝榴石 + 夕线石 = 尖晶石 + 石英等平衡的连续反应。对近期关于各个变质相热压力测定的文献进行的广泛调查揭示了每个相中遇到的P - T范围。温度估计与特纳（1968）的推论非常吻合。压力测定表明，在12 - 16千巴的压力范围内，蓝片岩相、角闪岩相和麻粒岩相转变为榴辉岩相。
Summary Information on pressure (P) and temperature (T) is a fundamental aspect of research on metamorphic terrains. Unfortunately, many workers employ thermobarometers that are not experimentally calibrated, are insensitive or too sensitive to P-T changes, depend on a priori assumptions of water pressure (such as most petrogenetic grids), or are rapidly reset on cooling. Many systems are based on inaccurate thermodynamic data, involve solids with inadequately characterized structural states, neglect effects of thermal expansion and compressibility, or require long extrapolations in P-T-X space. For instance, application of the widely used garnet-clinopyroxene KD thermometer may require extrapolation to temperatures where current thermodynamic models of pyroxenes and garnets remain uncertain. Current versions of the Mg/Fe exchange thermometer for biotite-garnet involve substantial compositional extrapolations for many applications and the biotite is easily reset while cooling from higher T. The most widely employed barometer is based on dilution of the reaction grossular + kyanite + quartz = anorthite, but failure to correct molar volumes for P-T-X may yield systematic errors of 1–2 kbar for barometry of crustal metamorphites. Application of this barometer to rocks equilibrated at T < 600–650°C is presently unwarranted in view of unknown a-X relations of garnets and plagioclases at these T. However, by careful selections, thermobarometry may be accurate to ±50°C and ±1 kbar in many metamorphic terrains if a variety of different equilibria can be applied. Well-calibrated barometers that are useful for T τ 600–650°C rely on continuous reactions based on equilibria such as almandine + rutile = ilmenite + sillimanite + quartz, garnet + quartz = ferrosilite + plagioclase, garnet + rutile = ilmenite + anorthite + quartz, and almandine + sillimanite = hercynite + quartz. An extensive survey of the recent literature on thermobarometry of individual metamorphic facies reveals the range of P-T encountered in each facies. Temperature estimates are in good agreement with the inferences of Turner (1968). Barometry reveals that the blueschist, amphibolite and granulite facies give way to the eclogite facies over the pressure range of 12–16 kbar.