存在初始“传导盖层”的月球岩浆洋演化与月壳成因  

Evolution of lunar magma ocean and crust formation under initial conductive lid

作　　者：许英奎[1] 李雄耀[1] 朱丹[2] 王世杰[1,3] 

机构地区：[1]中国科学院地球化学研究所月球与行星科学研究中心,贵阳550081 [2]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵阳550081 [3]中国科学院地球化学研究所环境地球化学国家重点实验室,贵阳550081

出　　处：《岩石学报》2016年第1期1-9,共9页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41490634;41490635;41373068;41503065)资助

摘　　要：月球早期经历了岩浆洋阶段,岩浆洋的研究对认识月球内部构造有着重要意义。月球岩浆洋演化主导模型认为:岩浆洋结晶到80%左右,斜长石开始结晶,并上浮形成斜长岩月壳。该模型与观察事实存在两点矛盾:1)基于该模型计算结晶的斜长石An牌号比高地样品斜长石An牌号测试结果低;2)该模型散热速率计算指示岩浆洋在几个百万年时间内固化,而同位素体系对月球岩石样品定年结果表明月壳的结晶年龄十分古老,并且结晶区间跨越了270Myr,这与主导模型之间存在矛盾。以解决以上两点矛盾为目的,本文论证岩浆洋在演化之初硕部存在冷却"盖层",并将硅酸盐熔体在温度梯度下的热扩散效应引入岩浆洋演化模型。热扩散效应指均一的物质在温度梯度下发生分异的过程。本文工作模型是:由于月球的重力常数小,不能有效的保持大气,因此月球的岩浆洋表面温度很低。此时岩浆洋自上而下存在一个过渡的瞬态固化"盖层"(淬火层),岩浆洋自上而下存在温度梯度,岩浆洋在该梯度下发生热扩散效应(Soret效应),Soret效应导致上部结晶斜长石的熔体富Ca和贫Na,因此结晶的斜长石An牌号高。The early state of the Moon is thought to be Lunar Magma Ocean （LMO）. Studies of LMO not only have significant meaning for recognizing the internal structure of the Moon, but also can be indicative for the origin of the Moon and planets. The dominated model of the LMO suggests that after 80% of the LMO solidified, plagioclase starts to crystallize and floats to the surface to form anorthositic crust and the whole solidifying time for the LMO is only several million years. The dominated model has discrepancy with the Apollo observations that crystallization age of anorthosites span 270Myr. To solve this problem, we focus on the temperature gradient in the LMO and apply mass transport under thermal gradient to its evolution. Chemical heterogeneity can occur in the initially homogenous silicate melt under thermal gradient, which is named thermal diffusion. Our working model is： the LMO is stratified in composition, and the lunar crust is formed from the upper part-the partially crystallizing zone. Calculations of An of plagioclase and the speed of diapirs also support this crust-forming model.

关 键 词：月球 岩浆洋 斜长岩月壳 热扩散 

分 类 号：P691[天文地球—地质学]