硅酸盐岩浆的Fe^(3+)—Fe^(2+)平衡与氧逸度

FERRIC-FERROUS EQUILIBRIUM AND OXYGEN FUGACITY IN SILICATE MAGMAS

铁是硅酸盐岩浆中唯一呈两种价态存在的主要元素.岩浆中Fe^(3+)——Fe^(2+)的平街不仅显著地影响岩浆结晶作用的趋势,而且由于Fe^(3+)和Fe^(2+)在熔体相中具有不同的结构作用,从而影响熔体的性质,如密度和粘度等.氧是岩浆中具有相当化学活动性的组分.岩浆演化过程中氧逸度的变化明显地影响岩浆的结构、流变学性质和化学成分.对岩浆中Fe^(3+)——Fe^(2+)平衡的研究,可以获得有关氧逸度变化的信息,因而具有重要的岩石学意义.

This paper deals with the iron oxidation reaction in silicate magmas. Various approaches to this subject,especially those in the last decade,have been reviewed,with focus on both the thermody-namical model of the iron redox reaction in silicate liquids and the dependence of oxygen fugacity on pressure in magmas. It is concluded that,according to the partial molar volumes of oxides in silicate liquids (Lange et al. ,1987)and the stoichiometric model of the iron oxidation reaction in silicate melts (Kress et al. , 1988) .oxygen fugacity may have much smaller dependence on the pressure of petrologi-cal interest,compared with the model of Sack et al. (1980).