黑龙江省上古生界伊利石的成因标志及其地质意义

Genetic Chariciterics of the Illite from the Upper Paleozoic Group in Heilongjiang Province and Its Geological Significance

采用XRD技术,对黑龙江省上古生界泥质岩石中伊利石结晶度、多型和b值进行了测定,以揭示该区晚古生代极低级变质作用特征。测定结果表明,伊利石结晶度(Kübler指数)主要变化于0.31～0.77°Δ2θ,伊利石(白云母)b值主要变化于8.983～9.011,伊利石(白云母)多型为1Md型、1Md+2M1混合型和2M1型。上述伊利石矿物学参数揭示出,该区上古生界泥质岩石主体属于中—低压相晚期成岩带-低级近变质带范畴。进一步的研究表明,伊利石b值和伊利石结晶度存在明显的负相关关系,即随伊利石b值的逐渐增大(压力升高),伊利石结晶度逐渐减小(温度升高),暗示伊利石形成于一种正常的与埋深有关的成岩-变质环境,继而揭示出该区上古生界的成岩作用与变质作用是一个统一的连续过程而不是两个相互无关的地质事件。结合区域地质背景和内蒙、吉林等地伊利石的研究成果可以认为,东北地区上古生界并未遭受大规模的绿片岩相区域变质作用,局部出现的某些绿片岩相(或更高级别)的变质岩应是动力变质作用或接触变质作用的产物。

In order to investigate the very low-grade metamorphism of the Upper Paleozoic group in Heilongjiang Province,the crystallinity,polytype and b dimension of illites from the argillaceous rocks have been measured by XRD technique.The results showed that the illite crystallinity（Kübler index） ranged mainly from 0.31 to 0.77 °Δ2θ,while the illite（muscovite） b dimension ranged mainly from 8.983 to 9.011,and the illite（muscovite） polytype presented three types of 1Md,1Md＋2M1 and 2M1.The mineralogical parameters of illites in above indicated that the argillaceous rock from the upper Paleozoic Group in the area belongs to the category from late diagenesis to very low-grade metamorphism.Moreover,there is a negative correlation between crystallinity and b dimension of illites,which shows crystallinity decreases（temperature increases） with the b dimension increases（pressure increases）.It is suggested that the illites formed in the normal geological background from diagenesis to metamorphism related to burial depth,which reveals that both diagenesis and metamorphism of the Upper Paleozoic Group in the area belong to an unitary and continuous process in stead of two independent and unrelated geological event.Combining the regional geological background and achievements in research of illites in Inner Mongolia and Jilin Province,it can be included that the main part of the Upper Paleozoic Group in Northeast China did not undergo a massive greenschist facies regional metamorphism.Some greenschist facies（or higher degree） metamorphic rocks in parts of the area should be resulted from dynamic or contact metamorphism.