岩浆系统橄榄石Fe-Mg互扩散的理论基础及其地质应用

Theoretical Basis and Geological Application of Fe-Mg Interdiffusion of Olivine in Magmatic System

了解岩浆在演化过程中的时间尺度具有重要的岩石学意义。橄榄石作为岩浆岩中主要的造岩矿物之一,为研究扩散年代学在岩浆系统中的应用提供了理想窗口。通过实验测定的不同条件下的橄榄石Fe-Mg互扩散系数,以及相关扩散模型的进一步完善,极大地推动了矿物内元素扩散年代学的发展。本文介绍了扩散年代学的基本原理和数学模型,并回顾和总结了以往实验岩石学的工作,提出温度、压力、氧逸度、水活度、橄榄石的成分和晶体的各向异性都会对橄榄石Fe-Mg互扩散产生影响。最后介绍了橄榄石Fe-Mg扩散模型在地质中的具体应用,其可以约束包括岩浆上升、演化、混合等不同地质过程的时间尺度。

It is of great petrological significance to unravel the time scale of a large range of magma residence times in different magmatic processes.Olivine as one of the major rock-forming minerals in igneous rock provides an ideal window for studying the application of diffusion chronometry in magmatic system.Improvement of Fe-Mg inter diffusion coefficient and diffusion model by advances in analytical and experimental approaches further provided new opportunities for diffusion chronometry in minerals.In this paper,we use olivine as a“reference case”to illustrate the theory and mathematical model of diffusion chronometry.On the basis of previous petrological experiments,we suggest that temperature,pressure,oxygen fugacity,water fugacity,chemical composition,and crystal anisotropy can inhibit or enhance Fe-Mg interdiffusion in olivine.We demonstrated the possible implications of olivine Fe-Mg diffusion model in natural systems and suggested that the zoning of different igneous minerals can be used to restrict the time scales of different magmatic processes from magma rising to magma transport,magma mixing and magma fractionation.