浙江煤山二叠系—三叠系界线附近黄铁矿及其硫同位素组成研究

Pyrites and Sulfur Isotopic Composition near the Permian-Triassic Boundary in Meishan, Zhejiang

运用地质学、矿物学、岩石学和地球化学等理论和方法,系统地研究了中国浙江长兴煤山二叠系—三叠系(P/T)界线附近黄铁矿的含量变化、矿物学特征、硫同位素组成及其垂向变化规律等,指出P/T界线附近黄铁矿高含量层位的成因与火山作用有关。研究发现,在浙江煤山长兴组顶部,紧靠P/T界线的第24e2分层石灰岩中,黄铁矿骤然增多,含量高达1.84%,比远离P/T界线的第22至24d分层石灰岩中的黄铁矿含量高出90多倍;硫同位素组成发生突变,δ34S值陡然上升为+2.2‰;其特征与火山气体总硫的同位素组成平均值极为相似,而与细菌还原黄铁矿的硫同位素组成完全不同。而且,在第24e2分层黄铁矿高含量层位中,还共生有较多β-石英等火山碎屑物质;岩石和黄铁矿中微量元素含量异常富集。因此认为,陆地和海底火山活动曾喷出大量的富含H2S的气体,造成古海洋局部最上层海水中富集大量硫化氢,为形成黄铁矿创造了条件。二叠纪、三叠纪之交,强烈的火山作用,使海洋生存环境急剧恶化,是造成海洋生物相继灭绝的主要原因。

The content and crystal form of pyrites, and sulfur isotopic composition of pyritic sulfur as well as its vertical distribution in the strata near the Permian-Triassic boundary in Meishan, Changxing County, Zhejiang Province, China were studied using theories and methods of geology, petrology, mineralogy and isotopic geochemistry. It is pointed out that the genesis of mass pyrites in the top Permian limestone bed may be correlated with volcanism. Research result indicates that the limestone bed （bed 24es, closely adjacent to the P/ T boundary） has the highest pyritic content （1.84%）, which is 90 times the content of other beds （bed 22 to bed 24d） far away from the P/T boundary. It has an abnormally high δ 34^S value of ＋2.2‰, which is very similar to the average value of volcanic gas, but is completely different from the value of bacteria reduced pyrites. Furthermore, there are many volcanic products such as β-quartz and siliceous cylinder and siliceous spherules in bed 24e2, and the contents of trace elements in pyrites and limestone are anomalously high in bed 24e2 and bed 24f. So, the geological event causing volcanic eruption with mass H2S gas production led end-Permian. the massive extinction may be volcanism, to the enrichment of mass H2S at the ocean and submarine surface in the end-Permian.