摘要
在中国大陆科学钻探主孔榴辉岩中发现了重晶石。重晶石以包裹体形式保存在石榴子石中,多为浑圆状,表面积平均约250μm2。通过电子探针测试,重晶石中SrO含量大多超过20%,为锶重晶石,其化学分子式为(Ba0.4836~0.6180Sr0.3787~0.4722Ca0.0064~0.0889)S0.9688~0.9963O4。同时还发现榴辉岩中的石榴子石有柯石英假象,温压条件计算表明该榴辉岩的峰期温压条件为696~730℃,2.9~3.2GPa。电子探针成分测定包裹这些重晶石的石榴子石为峰期变质矿物,这进一步说明重晶石也经历过超高压变质。重晶石通常形成于强氧化和高盐度流体作用的条件下,本文的研究表明超高压变质过程中至少出现了一定范围内的强氧化环境和高盐度流体作用,但其地球动力学意义有待进一步研究。
Barite was found as inclusions in garnet of eclogite from the main borehole core of the Chinese Continental Scientific Drilling. The barite is nearly round in shape, and the little round only has the area of about 250 μm~2 in average. The electron-microprobe(EMP) data indicates that the content of SrO is more than 20% in the barite, and it can be callded strontium barite. Its chemical formula is (Ba_ 0.4836~0.6180 Sr_ 0.3787~0.4722 Ca_ 0.0064~0.0889 )S_ 0.9688~0.9963 O_4. The quartz pseudomorph after coesite has been found in garnet, and the calculated peak metamorphic P-T conditions are 2.9~3.2GPa , 696~730℃ respectively. Synchronously, The EMP data indicates that the garnet which includes the barite was formed during the peak metamorphic progress, it is proved again that the barite underwent the UHP metamorphism. Barite is generally formed in the fluid process of high salinity and heavy oxidation. This study reflects that heavy-oxidation condition and high-salinity fulid process happened at least to a certain extent of rock during the UHP metamorphism, and its geodynamical significance needs further study.