龟山岛附近海底热液自然硫烟囱体的硫同位素研究

SULFUR ISOTOPE OF SUBMARINE SULFUR CHMNEYS NEAR KUEISHAN ISLAND

利用稳定同位素质谱仪对龟山岛附近海底热液自然硫烟囱体分层取样的硫同位素分析,获得了自然硫烟囱体的硫同位素特征。结果表明,龟山岛附近海底热液自然硫烟囱体的δ34S值变化不大,幅宽只有0.913,说明自然硫的来源较为单一,受控因素相对较少。根据硫同位素值的特征,划分出三种类型的烟囱体,它们是由热液流体中的硫同位素值和海水与烟囱体外壁的反应来控制,Ⅰ型烟囱体、Ⅱ型烟囱体的外壁与海水发生化学反应,形成一定量的自然硫沉淀,烟囱体的生长是向内、向外两个角度同时生长;Ⅲ型烟囱体则主要是向内一个角度生长。热液流体中的δ34S值(H2S)随时间的变化是由于海水端元和玄武岩端元不同比例的混合所致。

Composition and distribution of isotopic sulfur were studied for samples taken in situ （24°50＇N/ 121°57＇E） between 10-20 m underwater from different layers of submarine sulfur chimney near Kueishan Island, a live volcano in an active tectonic background northeast of Taiwan Island. Six sets of three samples were collected in horizontal direction from outside to inside of the chimney （built up by native sulfur underwater） in 3 corresponding color layers named A, B, and C. Stable isotope of native sulfur samples were measured. The results show that the δ^34S values of the samples varied slightly at ±0.913, indicating a single and common source and less impacted by environmental factors. In terms of the isotopic feature, three types （Ⅰ, Ⅱ and Ⅲ） were classified. Hydrothermal fluid inside the chimney and the reaction between seawater and the outer-layer of chimney may have affected the ± value. The outer-layer of Ⅰ - and Ⅱ -typed chimneys reacted with seawater and produced native sulfur bearing sediments that accumulated from both outside and inside, whereas Ⅲ-typed chimney from inside. In addition, various δ^34S values in H2S from hydrothermal fluid in different layers were believed to be resulted from the mixing between end compositions of seawater and basalt in different proportions.