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Re-examining the role of chondrules in producing the elemental fractionations in chondrites

机译:重新审查球粒状元素在球粒状元素产生中的作用

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The matrices of all primitive chondrites contain presolar materials (circumstellar grains and interstellar organics) in roughly CI abundances, suggesting that all chondrites accreted matrix that is dominated by a CI-like component. The matrix-normalized abundances of the more volatile elements (condensation temperatures < 750-800 K) in carbonaceous and ordinary chondrites are also at or slightly above CI levels. The modest excesses may be due to low levels of these elements in chondrules and associated metal. Subtraction of a CI-like matrix component from a bulk ordinary chondrite composition closely matches the average composition of chondrules determined by instrumental neutron activation analysis (INAA) if some Fe-metal is added to the chondrule composition. Measured matrix compositions are not CI-like. Sampling bias and secondary redistribution Of elements may have played a role, but the best explanation is that similar to 10-30% of refractory-rich, volatile depleted material was added to matrix. If most of the more volatile elements are in a CI-dominated matrix, the major and volatile element fractionations must be largely carried by chondrules. There is both direct and indirect evidence for evaporation during chondrule formation. Type IIA a
机译:所有原始球粒陨石的基质都含有大致CI丰度的前太阳物质(星际颗粒和星际有机物),这表明所有球粒陨石都分泌出以CI样成分为主的基质。碳质球粒陨石和普通球粒陨石中较易挥发的元素(冷凝温度<750-800 K)的基质归一化丰度也等于或略高于CI水平。适度的过量可能是由于这些元素在软骨和相关金属中含量较低。如果将一些铁金属添加到球状晶组成中,则从块状普通球状晶组成中减去CI样基体成分与通过仪器中子活化分析(INAA)确定的球状晶的平均组成非常匹配。测得的基质组成不像CI。元素的采样偏差和二次分布可能起了作用,但最好的解释是向基质中添加了约10-30%的难熔,易挥发的贫化材料。如果大多数较易挥发的元素都位于CI占主导地位的基质中,则主要和易挥发元素的分馏必须主要由软骨组成。软骨形成过程中有直接和间接的蒸发证据。 IIA型

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