变质相平衡在研究深熔岩石中的应用

Application of metamorphic phase equilibrium to study anatectic rocks

下地壳岩石的深熔作用不仅与麻粒岩和花岗岩的形成具有紧密关联,而且在某些构造环境下会对地球动力学演化过程造成影响,因此,对深熔岩石的变质P-T条件的准确估算及对其熔融机制的限定具有重要意义。基于内洽性热力学数据库、THERMOCALC/Perple_X等程序以及适当的固溶体活度模型,变质相平衡模拟已逐渐成为变质岩石学的常规研究方法,广泛应用于推断天然岩石的矿物共生序列、估算岩石的变质P-T条件等。不仅如此,如果有适当的熔体活度模型,变质相平衡模拟还能估算深熔岩石的熔融温度、压力及熔体比例,以及限定其涉及的熔融反应,并计算熔体、转熔矿物及残余矿物的成分等。针对不同成分岩石,包括花岗质岩石、变泥质岩、变基性岩及橄榄岩在不同压力下产生的熔体,前人陆续提出了对应的活度模型,并且其有效性得到了相关实验数据的验证。随着近年来熔体活度模型的不断更新和完善,变质相平衡模拟有望成为研究自然界深熔岩石的常规方法,为相关的麻粒岩和花岗岩成因研究、相关地球动力学演化研究提供新的思路。

Anatexis of lower crustal rocks is not only closely associated with the formation of granulite and granite, but also can affect the geodynamic evolution processes in some tectonic environments. Based on internally consistent thermodynamic database, programs like THERMOCALC/Perple_X and appropriate activity-composition models for solid solutions, metamorphic phase equilibria modeling has gradually become a common research method in metamorphic petrology, and is widely used for the deduction of mineral paragenesis, estimation of the metamorphic P-T conditions of natural rocks, etc. Moreover, if proper activity-composition models for melt exist, metamorphic phase equilibria modeling can be used to estimate melting temperatures, pressures and the proportion of melt, to confirm involved melting reactions, and to calculate compositions of melts, peritectic minerals and residual minerals. For melts derived from rocks of different compositions, including granitic rocks, meta-pelites, meta-basic rocks and peridotites under different pressures, previous researches have successively raised associated activity-composition models, which have been confirmed to be valid according to related experimental data. Along with the successive updates and improvement of activity-composition models for melts in recent years, metamorphic phase equilibria modeling is anticipated to become a common method to study natural anatectic rocks, and provide new research avenues to discuss granulite and granite formation, and associated geodynamic evolutions.