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Density measurements of basaltic magma at high-pressure and high-temperature using X-ray absorption method

X射线吸收法测量高压高温玄武岩浆的密度

基本信息

批准号：
16340170
负责人：
URAKAWA Satoru
金额：
$ 10.5万
依托单位：
OKYAMA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-16340170/
关键词：
magma density equation of state synchrotron radiation high-pressure

项目摘要

Density of magma is one of the important physical properties to control the transportation of magma in the Earth and planetary interiors. We have established the new technique to measure the density of magma under pressure by using large volume high-pressure apparatus and synchrotron radiation, on which X-ray absorption is based. We have measured the density of mid-ocean ridge basalt (MORB) magma up to about 5 GPa and 2000K by suing high-pressure X-ray absorption technique, which is the most abundant magma on the Earth and the Earth-like planets. Experiments were carried out using the cubic press, SMAP1, installed at BL22XU of SPring-8, where a highly brilliant monochromatic X-ray is available. The basaltic magma was confined in the single crystal diamond capsule that is X-ray transparent rather than silicate, the hardest material, which is uniformly deformed under pressure, and chemically inert with magma. Absorption of X-ray from the basaltic magma was measured up to 4.6 GPa and 1900 K, and density was calculated from Lambert-Beer law, I = I_0exp(-μpt). X-ray absorption measurements give the density of basaltic magma along its melting curve. Fitting the Birch-Murnaghan equation of state to density data yields anomalous negative pressure derivative of the bulk modulus of the basaltic magma. This means the basaltic magma becomes more compressible at higher pressure, opposite to the normal crystalline solid. This result strongly indicates that the structure of basaltic magma is changing with increasing pressure, including the shrinkage of networks of SiO_4 and AIO_4 tetrahedra and the increase of the coordination number of aluminum ions.

岩浆密度是控制岩浆在地球和行星内部运移的重要物理性质之一。我们建立了用大体积高压装置和同步辐射测量压力下岩浆密度的新技术，它是X射线吸收的基础。利用高压X射线吸收技术测量了地球和类地行星上最丰富的大洋中脊玄武岩(MORB)岩浆的密度，最高可达5 Gpa和2000K。实验是使用安装在Spring-8的BL22XU上的SMAP1立方压力机进行的，在那里可以获得高亮度的单色X射线。玄武岩岩浆被限制在单晶金刚石胶囊中，该胶囊是X射线透明的，而不是硅酸盐，硅酸盐是最坚硬的材料，在压力下均匀变形，与岩浆具有化学惰性。测得玄武岩岩浆对X射线的吸收达到4.6GPa1900K，密度由朗伯-比尔定律i=I0exp(-μpt)计算。X射线吸收测量给出了玄武岩岩浆沿其熔融曲线的密度。将Birch-Murnaghan状态方程与密度数据进行拟合，得到玄武岩岩浆体模的反常负压导数。这意味着玄武岩岩浆在较高的压力下变得更具可压缩性，与正常的结晶固体相反。这一结果有力地表明，玄武岩岩浆的结构随着压力的增加而发生变化，包括SiO_4和AlO_4四面体网络的收缩和铝离子配位数的增加。