Partitioning of Ca and Al between forsterite and silicate melt in dynamic systems with implications for the origin of Ca, Al‐rich forsterites in primitive meteorites
Partitioning of Ca and Al between forsterite and silicate melt in dynamic systems with implications for the origin of Ca, Al‐rich forsterites in primitive meteorites
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动态系统中镁橄榄石和硅酸盐熔体之间 Ca 和 Al 的分配对原始陨石中富含 Ca、Al 的镁橄榄石起源的影响
DOI：
10.1111/j.1945-5100.2003.tb00312.x
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发表时间：
2003
影响因子：
2.2
通讯作者：
H. Palme
中科院分区：
文献类型：
--
作者：
A. Pack;H. Palme
本文报道了为研究快冷钙铝熔体中钙铝在镁橄榄石与熔体之间分配关系而设计的动态晶化实验结果。钙在橄榄石和硅酸盐熔体之间的分配在1.5℃/小时到1000℃/小时的范围内与冷却速度无关，在CaO含量高达25wt%的范围内。在分析不确定的情况下，我们的数据绘制在Libourel(1999)获得的平衡分配曲线上。Al在高冷却速率下的分配行为更为复杂。铝在橄榄石和共生熔体中的分布比钙更不均匀。但Al分配系数随冷却速度的变化没有系统的变化趋势。我们将实验结果应用于钙、铝含量较高的陨石橄榄岩的形成。虽然这些橄榄岩经常存在于球粒陨石中，但其寄主球粒体内的钙含量太低，不足以结晶这些高钙橄榄岩。球粒陨石熔体的快速冷却也是如此。这些橄榄岩的母质熔体要求CaO含量在20wt%以上。
Abstract— We report the results of dynamic crystallization experiments that were specifically designed to study the dependence of Ca and Al partitioning between forsterite and melt in rapidly cooling Caand Al‐rich melts. The partitioning of Ca between olivine and silicate melt is found to be independent of the cooling rate within the range of 1.5 to 1000°C/hr and at CaO contents of up to 25 wt%. Within analytical uncertainty, our data plot on the equilibrium partitioning curve obtained by Libourel (1999). The partitioning behavior of Al at high cooling rates is more complex. Aluminum is much more heterogenously distributed in the olivine and the co‐existing melt than Ca. But, no systematic trend of Al partition coefficient with cooling rate is observed. We apply the results of the experiments to the formation of meteoritic forsterites with relatively high contents of Ca and Al. Although these forsterites are found frequently inside chondrules, the Ca contents of their host chondrules are far too low to crystallize these high Ca‐forsterites. This is also true for very rapid cooling of chondrule melts. The parental melt of these forsterites requires CaO contents above 20 wt%.