Chemical fractionations in meteorites—III. Major element fractionations in chondrites
Chemical fractionations in meteorites—III. Major element fractionations in chondrites
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DOI：
10.1016/0016-7037(70)90112-2
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发表时间：
1970-03
影响因子：
5
通讯作者：
J. Larimer;E. Anders
中科院分区：
文献类型：
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作者：
J. Larimer;E. Anders
大约20种元素，包括球粒陨石物质的主要成分，在几个球粒陨石类中分离。我们试图解释这些分馏的假设，它们发生在太阳星云，从碳质球粒陨石组成的材料开始。1. (1)亲石元素（Al、Ca、Cr、Hf、Mg、Sc、Si、Th、Ti、U、Y、Zr和镧系元素）可能在1300-1350° K时通过早期凝析物的部分损失而分馏，由矿物如MgAl 2 O2、Mg 2SiO 4、CaTiO 3、Ca 2Al 2SiO 7等组成。(2)亲铁元素（Fe、Co、Ni等）在680 ~ 1050° K之间，金属和硅酸盐的部分分离使其分馏。这一阶段的氧化还原条件似乎因类而异，如分馏过程中硅酸盐中的Fe 2+ Mg 2+比值所示：普通硅酸盐为0.14±0.02，顽火辉石为0.00±0.07，碳质方解石为0.14±0.08或0.08±0.07。这种分馏可能是基于金属的铁磁性质，因为它显然发生在居里点以下。3. (3)软骨球的形成似乎与这些分离没有因果关系。它可能发生在约700° K的金属硅酸盐分馏过程中或之后，推测是由于尘埃的部分重熔。随后是挥发分的进一步冷凝和吸积。
Some 20 elements, including the major constituents of chondritic matter, are fractionated among the several chondrite classes. We have tried to explain these fractionations on the assumption that they occurred in the solar nebula, starting from material of carbonaceous chondrite composition. 1.(1) Lithophile elements (Al, Ca, Cr, Hf, Mg, Sc, Si, Th, Ti, U, Y, Zr, and lanthanides) may have been fractionated at 1300–1350° K by partial loss of an early condensate, consisting of minerals such as MgAl 2 O 2, Mg 2 SiO 4, CaTiO 3, Ca 2 Al 2 SiO 7, etc. 2.(2) Siderophile elements (Fe, Co, Ni, etc.) apparently were fractionated between 680 and 1050° K, by partial separation of metal and silicate. Redox conditions at this stage seem to have varied from class to class, as indicated by the Fe 2+ Mg 2+ ratio in the silicates during fractionation: 0.14±0.02 for ordinary, 0.00±0.07 for enstatite, and 0.14±0.08 or 0.08±0.07 for carbonaceous chondrites. This fractionation may have been based on the ferromagnetic properties of the metal, since it apparently took place below the Curie point. 3.(3) Chondrule formation does not seem to have been causally related to either of these fractionations. It may have occurred at~ 700° K during or after metal-silicate fractionation, presumably by partial remelting of the dust. It was followed by further condensation of volatiles and accretion.