月球岩浆洋演化的实验岩石学研究进展

Advances in experimental petrology study on the evolutionof the lunar magma ocean

由于缺少直接来自月球深部的岩石样品,实验和计算模拟是认识早期月球演化过程的有效方法和手段。20世纪70年代以来,陆续开展了大量的实验岩石学和实验地球化学工作对月球岩浆洋(lunar magma ocean,LMO)演化模型进行验证和修正。但是,学界对LMO模型中的两个关键性参数,即初始物质组成和熔融深度,仍然存在不同的认识。根据月震和重力探测数据推测的平均月壳厚度的差异、月球样品含水量的研究以及新的遥感数据解译发现月表广泛分布富镁铝尖晶石(Cr#<5)等等,直接影响我们对月球初始物质组成和LMO深度以及月球深部高压矿物相的评估。本文通过整理高温高压实验岩石学和实验地球化学在研究LMO演化方面的一系列研究成果,主要聚焦以下几个科学问题:(1)月球初始物质组成中的难熔元素和挥发分含量,以及LMO深度对月壳厚度、结晶矿物的种类及含量有着决定性的影响;(2)高压矿物相石榴子石在月球深部稳定存在的可能性及其对残余岩浆中微量元素的分配行为的制约;(3)特殊类型的月球样品(包括火山玻璃、镁质岩套等)的成因机制对月球深部物质组成具有指示意义;(4)月核的不同物质组成对LMO模型的初始成分含量,特别是微量元素的限定作用。我们以最新的观测数据和月球样品的分析结果为依据,对已有的LMO演化模型进行重新评估,提出月球深部含有石榴子石的LMO演化模型的可能性,并对该方向亟需开展的工作进行探讨。

Due to the lack of rock samples directly from the deep part of the Moon,experiments and numerical simulation are effective methods to understand the early evolution of the Moon.Since the 1970s,the Lunar Magma Ocean(LMO)evolution model has been verified and modified by a large number of experimental petrology and geochemical work.However,the original composition of the Moon and the depth of its magma ocean,which are the two most critical parameters of LMO models remain controversial.The different lunar crust thickness estimated from lunar seismic data compared to that estimated from gravity data,the volatile content of lunar samples,and the widespread of Mg and Al-rich spinel(Cr#<5)discovered from interpreting the new remote sensing data affect our assessment on the starting composition and the depth of LMO,and the fractional crystallization process thereafter.In this paper,we review a series of high temperature and high pressure experimental petrology and experimental geochemistry results on the Moon s early evolution by focusing on:(1)The influence of refractory elements and volatile content of LMO s composition and its depth on the thickness of lunar crust and the Moon s mineral constitution formed through early differentiation.(2)The rationality of stability of high pressure mineral garnet deep inside lunar mantle and it effect on the distribution of trace elements during the evolution of lunar.(3)The petrogenesis of the Moon s special components,including volcanic glasses and Mg-suite,and their indication on the composition of the Moon s deep interior.(4)The constraint of lunar core composition on the Moon s material source,especially the abundance of trace elements.Based on the latest observation and the new analysis results of lunar samples,we evaluate the existing LMO evolution models and propose a LMO model with garnet as an important constituent mineral inside the Moon.We also discuss the necessary work need to be done to improve the“new”LMO model.