变质地质学中的扩散:原理、前沿应用和问题

Diffusion in metamorphic geology:Principles,applications,and problems

变质地质学的研究离不开变质反应动力学。元素扩散具有完备的数理基础和丰富的实验数据,相对成熟地应用于变质地质学,是目前变质反应动力学的研究热点。本文从变质岩石学的视角,对扩散的基本数理原理、矿物元素扩散系数及其影响因素、扩散在变质地质学中的应用及其存在的问题做了系统的介绍和总结。本文强调,元素扩散是变质岩中普遍存在的动力学过程,一方面会改造矿物原始的生长环带,给传统温压计和相平衡模拟确定温压条件造成困恼,另一方面也给变质作用的研究带来动力学视角,为限定变质-构造热事件的时间尺度和速率提供精准的标尺,比如扩散速率计或者扩散年代学。扩散这种动力学方法在变质地质学中的应用和进一步发展仍需未来工作。

Kinetics is an indispensable part in the study of metamorphic geology.With the developing solid theoretical foundation and abundant experimental data in recent years,diffusion is becoming a hotspot of kinetics research in decoding metamorphic-tectonic processes.This study systematically summarizes basic mathematical principles of diffusion,diffusion coefficients and their influence factors,and introduces application of diffusion in metamorphic geology and its relevant problems.We highlight that intracrystalline diffusion is a ubiquitous process in metamorphic rocks.On the one hand,diffusion modifies minerals’growth zonation,and thus brings unexpected challenges to conventional geothermobarometers and phase equilibria modeling in the aspects of P-T condition calculations and interpretation of mineral chemical zonation.On the other hand,diffusion modification provides a unique perspective to analyze durations and rates of metamorphic processes,known as geospeedometry or diffusion chronology.At the end,we state that the further development and application of diffusion in metamorphic geology need more future work.