南极陨石研究的启示Ι:早期太阳星云连续化学分馏作用的岩石化学证据

球粒陨石金属相的 Ir、Os、Co等亲铁元素的浓度随氧化程度的升高而显著增大 ,其浓度以及铁纹石 Co含量和橄榄石 Fa值均反映了球粒陨石的氧化 -还原程度具有连续变化的特征。根据铁纹石 Co含量、橄榄石 Fa值、低 Ca辉石 Fs值、金属相的 Ir、Os、Co浓度以及其他球粒陨石分类参数 ,可能存在介于 E与 H、H与 L、L与 L L以及 L L与 C之间的球粒陨石过渡型 ,即E/H、H/L、L/L L和 LL/C化学群 ,从而将原有的 9个球粒陨石化学群增加到 1 3个。球粒陨石氧化 -还原程度的变化特征以及球粒陨石过渡型的发现都表明早期太阳星云的化学分馏作用具有连续变化的特点。

INSPIRATION FROM STUDY OF ANTARCTIC METEORITES I: PETROLOGIC AND COMPOSITIONAL EVIDENCES FOR EARLY CONTINUOUS CHEMICAL FRACTIONATION OF THE SOLAR NEBULA

Bulk concentrations of Ir,Os,Co and the other siderophile elements of metal phase in chondrites increase significantly with degree of oxidation,Which,together with Co-Content of kamacite and Fa-content of olivine,reveal a continuous trend of variation of redox among chondrites.Intermediate groups of E/H,H/L,L/LL,and LL/C,lying between E and H,H and L,L and LL,LL and C,respectively,are proposed based on Co-content of kamacite,Fa-content of olivine,Fs-content of low Ca pyroxene,bulk concentrations of Ir,Os and Co of the metal phase and other criteria of classification.The discovery of intermediate groups increases the number of groups of chondrites from 9 to 13.Both the variation of redox among chondrites and the existence of intermediate groups of chondrites suggest a continuous chemical fractionation in the primordial solar nebula.