Brearley A J, Bajt S, Sutton S R
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque 87131, USA.
Geochim Cosmochim Acta. 1995 Oct;59(20):4307-16. doi: 10.1016/0016-7037(95)00249-y.
The concentrations of Ni, Cu, Zn, Ga, Ge, and Se in five, fine-grained chondrule rims in the highly unequilibrated CO3 chondrite ALH A77307 (3.0) have been determined for the first time by synchrotron X-ray fluorescence (SXRF) microprobe at Brookhaven National Laboratory. These elements are especially useful for tracing the role of condensation and evaporation processes which occurred at moderate temperatures in the solar nebula. Understanding the distribution of moderately volatile elements between matrix and chondrules is extremely important for evaluating the different models for the volatile depletions in chondritic meteorites. The data show that the trace element chemistry of rims on different chondrules is remarkably similar, consistent with data obtained for the major and minor elements by electron microprobe. These results support the idea that rims are not genetically related to individual chondrules, but all sampled the same reservoir of homogeneously mixed dust. Of the trace elements analyzed, Zn and Ga show depletions relative to CI chondrite values, but in comparison with bulk CO chondrites all the elements are enriched by approximately 1.5 to 3.5 x CO. The abundance patterns for moderately volatile elements in ALH A77307 chondrule rims closely mimic those observed in the bulk chondrite, indicating that matrix is the major reservoir for these elements. The close matching of the patterns for the volatile depleted bulk chondrite and enriched matrix is especially striking for Na, which is anomalously depleted in ALH A77307 in comparison with average CO chondrite abundances. The depletion in Na is probably attributable to the effects of leaching in Antarctica. With the exception of Na, the volatile elements show a relatively smooth decrease in abundance as a function of condensation temperature, indicating that their behavior is largely controlled by their volatility.
布鲁克海文国家实验室利用同步加速器X射线荧光（SXRF）微探针首次测定了高度不平衡的CO3球粒陨石ALH A77307（3.0）中五个细粒球粒边缘的镍、铜、锌、镓、锗和硒的浓度。这些元素对于追踪在太阳星云中等温度下发生的凝聚和蒸发过程的作用特别有用。了解中等挥发性元素在基质和球粒之间的分布对于评估球粒陨石挥发性亏损的不同模型极为重要。数据表明，不同球粒边缘的微量元素化学非常相似，这与电子微探针获得的主量和次量元素数据一致。这些结果支持这样一种观点，即边缘与单个球粒没有成因关系，而是都从同一均匀混合尘埃库中取样。在所分析的微量元素中，锌和镓相对于CI球粒陨石的值显示出亏损，但与整体CO球粒陨石相比，所有元素都富集了约1.5至3.5倍的CO。ALH A77307球粒边缘中中等挥发性元素的丰度模式与整体球粒陨石中观察到的模式非常相似，表明基质是这些元素的主要储存库。对于钠来说，挥发性亏损的整体球粒陨石和富集基质的模式紧密匹配尤为显著，与平均CO球粒陨石丰度相比，ALH A77307中的钠异常亏损。钠的亏损可能归因于在南极洲的淋滤作用。除了钠之外，挥发性元素的丰度随凝聚温度呈现相对平滑的下降，表明它们的行为在很大程度上受其挥发性控制。
