Chemical fractionation in iron meteorites and its interpretation
Chemical fractionation in iron meteorites and its interpretation
复制标题
铁陨石的化学分馏及其解释
DOI：
10.1016/0016-7037(72)90046-4
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发表时间：
1972
影响因子：
5
通讯作者：
E. Scott
中科院分区：
文献类型：
--
作者：
E. Scott
已发表的对铁陨石中痕量和微量元素的分析已汇编完成，并用瓦森定义的化学基团解释了分布。当在对数刻度上绘制每个元素与镍的关系图时，通常可以清楚地分解成组，一组中的所有成员都落在直线上的采样和分析误差范围内。IIia、b和IVa组的直线一般与IIa、b平行，绘制在更陡峭的坡度上。与Ga和QE不同的是，许多元素在一个群内表现出变化，可能接近所有铁陨石所显示的变化。第一组成员具有相当均匀的元素浓度，而这些元素在其他主要组中存在严重的分馏。第I族元素之间的相关性也较小，因此增加了更多可用于定义族的参数，从而加强了化学分类的遗传学意义。确认了LIA和LIB组之间以及ILIA和I11B组之间的关系。更重要的是元素分馏提供的铁陨石形成过程中的事件记录。发生了两次分馏，一次初级事件确定了每一群的主体成分，另一次次生事件使每一群中的元素发生了分馏。第I组似乎逃脱了二次分馏。对可能的分馏机制的研究表明，二次过程发生在母体铁芯凝固期间。As、Au、Co、Mo、P、Pd、Sb等元素在早期贫镍固体中富集，与Ni呈正相关。这些趋势在很大程度上是从铁的二元相图中预测的，尽管铬和锗的表现不同。根据元素在固体和液态Fe-Ni之间的分配系数，可以预测分馏的大小。不幸的是，这些只能是猜测，还有待实验来证实它们的大小。在缩合过程中，可能发生了初级分馏，这种分馏建立了基团之间的化学差异。
Published analyses of trace and minor elements in iron meteorites have been compiled and the distributions interpreted with the chemical groups defined by Wasson. When each element is plotted against Ni on log scales, groups are often clearly resolved with all the members of a group falling within the limits of sampling and analytical error on a straight line. The lines for groups IIIa,b and IVa are generally parallel with IIa,b plotting on a steeper gradient. In contrast to Ga and Qe, many elements show variations within a group which may approach that shown by all the iron meteorites. Group I members have a fairly uniform concentration of elements which are severely fractionated in the other major groups. There are also fewer correlations of elements in group I.Thus the genetic significance of the chemical classification is strengthened by the addition of more parameters which may be used in the definition of the groups. Relationships between groups lia and lib and between Ilia and Illb are confirmed. More important is the record of events during the formation of iron meteorites that the fractionations of elements provide.Two fractionations have occurred, a primary event which established the bulk composition of each group and a secondary event which fractionated the elements within each group. Group I appears to have escaped the secondary fractionation. An examination of possible fractionation mechanisms suggests that the secondary process took place during solidification of iron cores in the parent bodies. The elements It, Os, Pt, Bu and Rh would be enriched in the early Ni-poor solid whilst As, Au, Co, Mo, P, Pd and Sb would concentrate in later solid and produce the observed positive correlations with Ni. These trends are largely those predicted from the binary phase diagrams of Fe, although Cr and Ge behave otherwise. The magnitude of the fractionations could be predicted from the distribution coefficients of elements between solid and liquid Fe-Ni. Unfortunately these can only be guessed and confirmation awaits experiments to indicate their magnitude. The primary fractionation which established the chemical differences between the groups might have occurred during condensation.