高温高压条件下镁铝-铁铝-钙铝三端元石榴子石热弹性性质研究

Garnet is an important mineral of the upper mantle and ultra high pressure metamorphic rocks. A lot of studies have revealed that most of the garnets from upper mantle (mantle xenoliths) and ultra high pressure metamorphic rocks are pyrope-almandine-grossular ternary garnet. However, up to date, there are no a systemic study about the PVT equation of state of pyrope-almandine-grossular ternary garnet. Large deviations will be caused by using the thermoelastic properties of unitary or binary garnet instead of ternary garnet to discuss the properties of the pyrolite and eclogite, which will result in misunderstanding the geodynamic processes of upper mantle and subduction zone. In this project, the PVT equation of state of pyrope-almandine-grossular ternary garnets which have different components will be investigated at high temperature and high pressure by using the resistance heating and laser heating diamond anvil cell. The effect of composition variance on the thermoelastic parameters of pyrope-almandine-grossular ternary garnets will be discussed, and then the quantitative density and thermoelasticity model (bulk modulus and its temperature and pressure derivatives, coefficient of thermal expansion, etc) of the eclogite and garnet-lherzolite shall be established. Finally, we will provide a key data to more accurately understand the thermoelastic behavior of mantle xenoliths and eclogite, which will give the basis for further understanding the geodynamical processes of the upper mantle and subduction zone.

石榴子石是上地幔以及超高压变质岩中的重要组成矿物。大量研究表明，上地幔以及超高压变质岩中的石榴子石绝大部分为镁铝-铁铝-钙铝三端元石榴子石。但目前未有关于镁铝-铁铝-钙铝三端元石榴子石PVT状态方程的系统研究报道。若以单端元或者二端元石榴子石代替三端元石榴子石的热弹性性质来约束地幔岩和榴辉岩的热弹性性质无疑将带来较大的偏差，这进一步影响到对上地幔和俯冲带的状态及其地球动力学过程的正确认识。本项目拟利用同步辐射X射线衍射技术结合电阻外加温以及激光加温金刚石压腔实验技术，在高温高压条件下对不同组分含量的镁铝-铁铝-钙铝三端元石榴子石进行PVT状态方程研究。讨论组分变化对镁铝-铁铝-钙铝三端元石榴子石热弹性参数值的影响，进而获得榴辉岩以及石榴子石二辉橄榄岩的定量密度和热弹性性质（比如体弹模量及其温压导数、热膨胀系数等）模型，为更准确地认识上地幔及俯冲带的热弹性行为和动力学过程提供关键的实验约束。

本项目以天然三端元石榴子石矿物为主要矿物样品，并结合部分人工合成三端元石榴子石样品，利用金刚石压腔外加温和同步辐射 X 射线衍射技术，在高温高压条件下，对三端元石榴子石样品进行 PVT状态方程研究。结合前人研究成果，探讨含水以及组分变化对三端元石榴子石矿物热弹性参数值的影响。项目执行期间，进行了数十次的高温高压同步辐射X射线衍射实验，获得了不同含水量及不同组分三端元石榴子石矿物的热弹性参数值，有效确定了含水和组分变化对三端元石榴子石矿物的稳定性及热弹性性质的影响。进而获得了榴辉岩的定量密度和热弹性性质模型，为更准确地认识上地幔及俯冲带的热弹性行为和动力学过程提供关键的实验约束。受本项目支持，已经发表各类学术论文24篇，其中SCI论文19篇，EI论文2篇，会议论文3篇。项目执行期间，共培养硕士生1名，博士生3名（获国家研究生奖学金1人次，中国科学院院长优秀奖1人次，中国科学院优秀博士论文奖1人次）。