西南印度洋中脊热液区烃类有机质组成及其成因意义

Composition and genesis implications of hydrocarbons in 49.6°E hydrothermal area,Southwest Indian Ocean Ridge

利用气相色谱（GC）、气相色谱-质谱联用仪（GC-MS）测定了西南印度洋中脊49.6°E热液区热液产物中的可溶有机质,结合生物标志物和单体同位素分析,对烃类有机质的组成、来源及成因意义进行了探讨。硫化物烟囱体以正构烷烃（3.437~3.962μg/g）为主要烃类,L/H〈1,C22以上烷烃具有轻微奇碳数优势（CPI=1.140~1.209）,NAR接近0;生物标志物类型丰富（Sq、IS40、烷基环己烷）,C31藿烷22S/（R＋S）高达0.77,且缺少17β（H）,21β（H）构型藿烷;低碳数饱和脂肪酸为主要脂肪酸类型,异构/反异构脂肪酸含量显著,缺少单不饱和脂肪酸。热液蚀变岩以异构烷烃（2.094μg/g）为主要烃类,正构烷烃以低碳数（L/H=1.33）、偶碳优势（CPI=0.377）为特征;脂肪酸以单不饱和脂肪酸为主。结果表明,海洋原生生物体是49.6°E热液区主要的烃类有机质输入源,热液流体温度及化学条件是控制热液喷口区原生生物群落分布及热液产物中烃类有机质组成的主要因素。生物标志物类型显示硫化物烟囱体中具有产甲烷古菌与硫酸盐还原菌共存的现象,反映出热液流体中富含H2,表明49.6°E热液区具有非生物合成烃类的可能。

Molecular composition of extractable and detectable organic matter in hypothermal product from49.6°E hydrothermal vent field were analyzed by GC and GC-MS.Combined with the analysis of biomarkers and individual isotopic composition,we discussed the composition,origin and genetic implication of hydrocarbons.N-alkanes（3.437-3.962μg/g）are the main hydrocarbon of sulfide chimney,with low L/H ratio（1）and slight odd carbon number predominance inC22alkanes（CPI=1.140-1.209）;NAR is close to 0.Sulfide chimney has a variety of biomarkers（Sq,IS40,cyclohexylalkanes）;22S/（R＋S）of C31 hopanes achieved 0.77;17β（H）and 21β（H）-hopanes were absent.The fatty acid of sulfide chimney is comprised of short chain saturated fatty acid and iso/anti-iso fatty acid,and lacks monounsaturated fatty acids.Iso-alkanes（2.094μg/g）are the main hydrocarbon of hydrothermal altered rock;n-alkanes are characterized by more low carbon（L/H=1.33）and even carbon number predominance（CPI=0.377）;monounsaturated fatty acids are the most abundant fatty acid.These results suggested that the autochthonous organisms were the major source of hydrocarbons in 49.6°E hydrothermal area,and that the temperature and chemical condition of hydrothermal fluid constrained the distribution of hydrothermal community and the composition of hydrocarbon of hydrothermal product.The molecular evidence for the abiogenic synthesis of organic compounds was rare,however,the coexistence of methanogens and sulfate reducing bacteria indicated that H2 were rich in hydrothermal fluids of 49.6°E vent and the abiogenic synthesis approach could not be neglected.