下地幔CaSiO_(3)钙钛矿的稳定性及其对LLSVPs的启示  

The stability of calcium silicate perovskite in the lower mantle and its implications for LLSVPs

作　　者：肖婷婷 张飞武[1] XIAO Ting-ting;ZHANG Fei-wu(State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,China;University of the Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]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,贵州贵阳550081 [2]中国科学院大学,北京100049

出　　处：《矿物学报》2022年第1期121-128,共8页Acta Mineralogica Sinica

基　　金：国家自然科学基金项目(编号:41773057,42050410319)。

摘　　要：LLSVPs的成因是当前固体地球科学研究的前沿热点,对这一成因的认识仍然存在很大的争议。认识LLSVPs的成因,对了解全球地幔对流性质、下地幔热结构以及化学物质的运输和演化等具有重要的科学意义。CaSiO_(3)钙钛矿(Ca-Pv)作为下地幔最丰富的矿物之一,也是近年来学术界关注的热点。Ca-Pv在下地幔条件下的晶体结构仍然是目前研究的主要问题之一,Ca-Pv能否与其结构和化学式都相近的含铁布里奇曼石形成固溶体?本文通过第一性原理地球化学计算,研究了Ca-Pv及固溶体的基态稳定性,弹性性质和地震波波速特性。研究结果表明,在20~120 GPa压力下,Ca-Pv最稳定的基态结构为四方结构。基态下Ca-Pv的弹性波速值低于Mg-Pv约5%。与非互溶体系相比,x(Fe)为0%~10%的固溶体体系,引起了-2%~0%的剪切波波速负异常;-1.2%~0%的纵波波速负异常;-0.45~0.15%的体波速异常。因此,推测固溶体Mg_(1-x-y)Ca_(x)Fe_(y)SiO_(3)可能作为下地幔LLSVPs的候选矿物组分之一。The origin and composition of LLSVPs is a currently frontier focus in the solid earth scientific research,but there is still no definitive answer as a lot of controversies remain.Studying the origin of LLSVPs is of essential scientific significance for understanding the properties of global mantle convection,the thermal structure of the lower mantle,and the transportation and evolution of chemical substances.As one of the main minerals in the lower mantle,Calcium silicate perovskite(Ca-Pv)is also the focus of academic attention in recent years.The crystal structure of the Ca-Pv in the lower mantle is still one of the main problems should be currently researched.One current unknown is whether the Ca-Pv and Fe-bearing Mg-Pv could form a solid solution as they have similar structures and chemical formulas.In this paper,the ground state stability,elastic properties and seismic velocity characteristics of the Ca-Pv and the solid solution have been calculated by using the first-principle theoretical geochemical calculation.The results show that the tetragonal structure is the most stable ground state of the Ca-Pv at pressures ranging from 20 GPa to 120 GPa.The elastic wave velocity of the Ca-Pv in the ground state is about 5%lower than that of the Mg-Pv.Compared with the non-miscible system,solid solutions with x(Fe)values varying from 0%to 10%could cause a drop in shear wave velocity(v_(s))of-2%-0%,a drop in P wave velocity(v_(p))of-1.2%-0%,and a change in body wave velocity(v_(o))of-0.45%-0.15%.Therefore,it is inferred that the solid solution of Mg_(1-x-y)Ca_(x)Fe_(y)SiO_(3) may be used as one of the candidate mineral components of LLSVPs in the lower mantle.

关 键 词：下地幔 CaSiO_(3)钙钛矿 固溶体 LLSVPs 

分 类 号：P57[天文地球—矿物学]