湘西晚前寒武纪层状硅质岩硅氧同位素组成及成因分析

SILICON AND OXYGEN ISOTOPIC COMPOSITIONS AND ORIGIN ANALYSIS OF LATE PRECAMBRIAN BEDDED CHERTS IN WESTERN HUNAN

湘西晚前寒武纪层状硅质岩硅氧同位素组成δ^(30)Si为0.0‰—0.7‰,δ^(18)O为20.2‰—23.6‰。利用δ^(30)Si和δ^(18)O分析硅质岩成,认为硅质岩为原生沉积,二氧化硅来源于热水,沉积在下斜坡边缘到棚缘盆地的环境中。根据燧石-海水间氧同位素平衡分馏方程计算岩石的形成温度为66.0—89.7℃,沉积温度低于66.0℃。

This paper reports the silicon and oxygen isotopic compositions of Late Precambrian bedded cherts for the first time. Their δ30Si values are 0. 0‰-0. 7‰ and δ18O 20. 2‰-23. 6‰. It is found that the δ30Si values in the section sequence roughly have a trend 'of change from values; By comparing δ30Si and δ18O values of the cherts with those of quartz and cherts of various origins, it is believed that the silica forming quartz was derived frorn hot water and the cherts are of primary sedimentary origin .δ30Si values show that the sedimentary environment was a transition zone between bathyal and abyssal zones. Calculation with the oxygen isotopic equilibration fractionation equation of chert - sea water shows formation temperatures of 66. 0 - 89. 7℃ and deposition temperatures below 66. 0℃.