青海省河南县三叠系伊利石结晶度与极低级变质作用

在开展“青海省河南县托叶玛地区I47E007023、I47E008023、I47E009023、1I47E009024四幅1∶5万区域地质矿产调查”时,为验证该地区三叠系变质情况,针对三叠系中泥岩(页岩)的伊利石结晶度做了分析测试。30件样品的实验结果表明北部宗务隆—泽库地层分区三叠系泥岩(页岩)伊利石Kübler结晶度指数为0.312~0.537,晶胞参数b0为0.8980~0.9032 nm,判断其变质温度小于350℃,具葡萄石-绿纤石和沸石相;南部西倾山地层分区三叠系泥岩(页岩)的伊利石Kübler结晶度指数为0.21~0.318,b0为0.8981~0.9014 nm,变质温度主要分布在200~350℃,局部>350℃,具葡萄石-绿纤石和绿片岩相。研究认为青海省河南县地区区域变质程度较低,为极低级变质作用或者未发生区域变质作用,且南部西倾山地层分区的变质程度略高于北部宗务隆—泽库地层分区变质程度。这一变质相带研究结论与前人认为的“区域低温动力变质作用及低绿片岩相变质带”不一致,变质程度相对更低。该研究证实了在青海省河南县地区三叠系地层中不存在大面积区域变质作用,仅存在极低级区域变质作用。

Crystallinity and metamorphism of illite from Triassic strata in Henan County of Qinghai Province

In order to verify the Triassic stratum metamorphism in this area, the crystallinity of illite in mudstone (shale) of Triassic stratum was analyzed and tested during the 1:50 000 regional mineral geological survey (I47E007023, I47E008023, I47E009023,1I47E009024)in Tuoyema area of Henan Mongolian Autonomous County in Qinghai Province. According to the experimental results of 30 samples, the crystallinity index of Triassic mudstone (shale) illite Kübler in Zongwulong-Zeku stratigraphic division in the north is 0.312-0.537, and the cell parameter b₀ is 0.898-0.903 2 nm. The metamorphic temperature is less than 350 ℃, with the grape-chlorite and zeolite facies. The crystallinity index of Triassic mudstone (shale) illite Kübler in the western inclined mountain stratigraphic division in the south is 0.21-0.318, and the b₀ value is 0.898 1-0.901 4 nm. The metamorphic temperature is mainly between 200 and 350 ℃, with the local temperature above 350 ℃ and grape-chlorite and greenschist facies. It is considered that the regional metamorphism grade in this area is very low or has no regional metamorphism. The metamorphism degree of the western dipping mountain stratum in the south is slightly higher than that of Zongwulong-Zeku stratum in the north. The measured metamorphic facies belts are not consistent with the previous thought, that is "regional low temperature dynamic metamorphism and low greenschist facies metamorphic belts", and the degree of metamorphism is relatively lower. It is confirmed that there is no large area regional metamorphism in the Triassic strata of Henan County in Qinghai Province, but only very low-level regional metamorphism.