Unlocking the zinc isotope systematics of iron meteorites
Unlocking the zinc isotope systematics of iron meteorites
复制标题
DOI：
10.1016/j.epsl.2014.05.029
复制
发表时间：
2014-08-15
影响因子：
5.3
通讯作者：
Schoenbaechler, M.
中科院分区：
文献类型：
--
作者：
Bridgestock, L. J.;Williams, H.;Schoenbaechler, M.
对IAB、IIAB和IIIAB群15个铁陨石的金属样品进行了锌同位素组成(增量锌-66)和浓度的测定。还分析了来自IAB铁托卢卡的硫铁矿和其他包裹体。此外，还给出了在1.5 Gpa和1650K下进行的金属-硅酸盐分配实验的第一批锌同位素数据。三个运行时间在10-60min之间的分配实验得到了一致的锌-硅酸盐分配系数，接近0.7，表明熔融金属和硅酸盐之间的锌同位素分馏很小(小于+/-0.2‰)或不存在。不同铁陨石组的金属锌含量范围不同，IIABS的浓度为0.08-0.24微克/克，IIIABS的浓度为0.8-2.5微克/克，IABS的浓度为12-40微克/克。相比之下，所有三个组的增量锌-66值(相对于JMC里昂锌)的范围都相似，从+0.5ppm到+3.0ppm，组间没有明显的系统差异。然而，在三角洲锌-66与1/锌的样地中，来自每一组的样本确定了明显的线性趋势，并且这些相关性得到了文献数据的支持。基于Toluca富铬矿包裹体的高锌含量和锌-66增量接近于0，模拟结果表明，锌的变化趋势可以用铬铁矿从金属相中的偏析来解释。这一过程可以解释所观察到的铁陨石金属的锌-三角洲-锌-66-铬体系，如果锌在铬铁矿中高度相容，并且锌的分配伴随着同位素分馏，其增量锌-66(CHR-MET)约为-1.5ppm。根据这些发现，IAB杂岩、IIAB和IIIAB铁陨石的母体很可能具有大约-1.0-+0.5ppm的增量锌-66值，这与对块体硅酸盐地球的锌同位素组成和球粒陨石的结果相似。综上所述，这意味着尽管锌含量有很大差异，但大多数太阳系天体都形成了相似的块状锌同位素组成。(C)爱思唯尔出版的2014年。
Zinc isotope compositions (delta Zn-66) and concentrations were determined for metal samples of 15 iron meteorites across groups IAB, IIAB, and IIIAB. Also analyzed were troilite and other inclusions from the IAB iron Toluca. Furthermore, the first Zn isotope data are presented for metal-silicate partitioning experiments that were conducted at 1.5 GPa and 1650 K. Three partitioning experiments with run durations of between 10 and 60 min provide consistent Zn metal-silicate partition coefficients of similar to 0.7 and indicate that Zn isotope fractionation between molten metal and silicate is either small (at less than about +/- 0.2 parts per thousand) or absent. Metals from the different iron meteorite groups display distinct ranges in Zn contents, with concentrations of 0.08-0.24 mu g/g for IIABs, 0.8-2.5 mu g/g for IIIABs, and 12-40 mu g/g for IABs. In contrast, all three groups show a similar range of delta Zn-66 values (reported relative to 'JMC Lyon Zn') from +0.5 parts per thousand to +3.0 parts per thousand, with no clear systematic differences between groups. However, distinct linear trends are defined by samples from each group in plots of delta Zn-66 vs. 1/Zn, and these correlations are supported by literature data. Based on the high Zn concentration and delta Zn-66 approximate to 0 determined for a chromite-rich inclusion of Toluca, modeling is employed to demonstrate that the Zn trends are best explained by segregation of chromite from the metal phase. This process can account for the observed Zn-delta Zn-66-Cr systematics of iron meteorite metals, if Zn is highly compatible in chromite and Zn partitioning is accompanied by isotope fractionation with Delta Zn-66(chr-met) approximate to -1.5 parts per thousand. Based on these findings, it is likely that the parent bodies of the IAB complex, IIAB and IIIAB iron meteorites featured delta Zn-66 values of about -1.0 to +0.5 parts per thousand, similar to the Zn isotope composition inferred for the bulk silicate Earth and results obtained for chondritic meteorites. Together, this implies that most solar system bodies formed with similar bulk Zn isotope compositions despite large differences in Zn contents. (C) 2014 Published by Elsevier B.V.