地幔流体化学组成与成烃

THE CHEMICAL COMPOSITIONS OF VOLATILES IN UPPER MANTLE AND THEIR IMPLICATION FOR HYDROCARBON GENERATION

采用分步加热质谱法测定了中国东部和美国西部的二辉橄榄岩捕虏体的流体组成,探讨了上地幔流体化学组成特征及对成烃的作用。指出:超临界态的地幔流体具有很强的溶解和扩散能力,是地球内部能量与物质向外传输的重要载体,其化学组成随地幔演化过程的不同而具有明显的差异;可划分出上地幔原始流体和交代作用流体等,上地幔原始流体组成与地幔源区密切相关,似原始地幔源区以CO为主,其次为CO2、H2,亏损地幔源区以CO2为主,其次为CO、H2,富集地幔源区含有较高的H2;中国东部上地幔交代作用过程中存在以CO2为主的再循环地壳交代流体;地幔流体自身含有一定数量的CH4和C2H6等烷烃组分及重烃组分,包括一定数量的原始烷烃组分;地幔流体含有较高的H2和热量,可为有机质生烃作用提供充足的氢源、热源及运移源动力。

Mantle fluids in supercritical state possess high dissolving and diffusing capacity, which are the important transporting carrier of energy in earth interior, their chemical compositions vary in a large range with the evolution processes of mantle, and can be distinguished as the primitive fluid in upper mantle, the fluid of mantle metasomatism and etc. The chemical composition of primitive fluid in upper mantle are related to the mantle reservoir, the primitive fluid in upper mantle with a primitive mantle-like reservoir is dominated by CO with secondary amounts of CO2 and H2; a depleted mantle reservoir shows a dominant CO2 with minor amounts of CO and H2 in primitive fluid in upper mantle, and an enriched mantle reservoir is enriched in H2. Meanwhile the fluids of mantle metasomatism were mixed by the recycled crustal fluid components beneath eastern China. Mantle fluids have preserved a certain amount light hydrocarbon, such as CH4, C2H6 etc. and high weight hydrocarbon, including an amount of primordial hydrocarbon, moreover, mantle fluid enriched in H2 and heat can provide the ample hydrogen and heat sources in hydrocarbon generation of kerogen and promote source rocks to expel hydrocarbons and migration.