(Table 1) Sulphur concentration and isotopic composition of ODP Leg 126 igneous rocks

Sulfur isotope ratios have been determined in 19 selected igneous rocks from Leg 126. The d34S of the analyzed rocks ranges from -0.1 â to +19.60 â. The overall variation in sulfur isotope composition of the rocks is caused by varying degrees of seawater alteration. Most of the samples are altered by seawater and only five of them are considered to have maintained their magmatic sulfur isotope composition. These samples are all from the backarc sites and have d34S values varying from +0.2 â to +1.6 â, of which the high d34S values suggest that the earliest magmas in the rift are more arc-like in their sulfur isotope composition than the later magmas. The d34S values from the forearc sites are similar to or heavier than the sulfur isotope composition of the present arc.本研究对大洋钻探126航次采集的19块选定火成岩开展了硫同位素比值测试。所分析岩石的δ34S值范围为-0.1‰至+19.60‰。该批岩石的硫同位素组成整体分异，其主控因素为海水蚀变程度的差异。多数样品均遭受海水蚀变，仅5块样品保留了原始岩浆硫同位素组成。上述保留原始组成的样品均采自弧后站位，其δ34S值介于+0.2‰至+1.6‰之间；其中较高的δ34S值表明，裂谷带早期岩浆的硫同位素组成较后期岩浆更趋近于弧岩浆特征。弧前站位样品的δ34S值与现今弧岩浆的硫同位素组成相近或偏重。