Characteristics and genesis of fluid inclusions from rocks of the early Precambrian khondalite series at Xinghe-Zhuozi district, Inner Mongolia.

According to morphology, occurrence, data of homogenization temperature and composition, various fluid inclusions from rocks of the khondalite series may be divided into three major groups. 1) The carbonic liquid inclusions w ith negative crystal form in sillimanite and quartz of peak metamorphism. T hey are the earliest ones and characterized by low X-H2O(0 similar to 17) a nd high carbonic material (XCO2+CH4 approximate to 70 similar to 90) with d ensity 1. 00 similar to 1. 05g/cm(3) corresponding to P approximate to 0. 7 GPa. Such inclusions may originally contain slightly higher water content t han the present one during their entrapment, but had experienced leakage of H2O in subsequent stage under a further dry and decompression environment. 2) Aqueous two-phase inclusions with X-H2O>80 similar to 85 and very low C O2 +CH4. They are most abundant in quartz of pegmatitic leucosomes and gran itic rocks, and represent the fluid appearing in their cooling stage. The D -L(H2O) of such fluid is 0. 93 similar to 0. 96g/cm(3) corresponding to P a pproximate to 0. 6GPa which is compatible with condition when the rapid dec ompression in this region was ended. 3) CO2-H2O two or three phases inclusi ons. They are the most widespread, and more frequently in clusters and in i ntragranular tails in quartz. The relative content of CO2+CH4 and H2O is co nsiderably variable. They are also characterized with lower density (0. 6 s imilar to 0. 8g/cm(3)) and low pressure about 0. 3 similar to 0. 4GPa, and may be originated by mixture of carbonic liquid from breaking of most inclu sions of peak stage and aqueous liquid of magmatic source. After entrapment , the further decrease of temperature to lower than 330 degrees C made such fluid separated to two or three phases.