Differentiation history of the mesosiderite parent body: constraints from trace elements and manganese-chromium isotope systematics in Vaca Muerta silicate clasts
Differentiation history of the mesosiderite parent body: constraints from trace elements and manganese-chromium isotope systematics in Vaca Muerta silicate clasts
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中菱铁矿母体的分化历史：Vaca Muerta 硅酸盐碎屑中微量元素和锰铬同位素系统学的限制
DOI：
10.1016/j.gca.2003.08.005
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发表时间：
2003
影响因子：
5
通讯作者：
D. Mittlefehldt
中科院分区：
文献类型：
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作者：
M. Wadhwa;A. Shukolyukov;A. Davis;G. Lugmair;D. Mittlefehldt
本文报道了Vaca Muerta中陨铁岩中几个玄武质和斜方辉石质碎屑的微量元素显微分布和53 Mn-53 Cr系统学研究结果。离子探针分析选定的微量元素和微量元素丰度矿物的硅酸盐碎屑表明，火成结晶后，这些碎屑经历了广泛的变质平衡，导致在内部和晶粒间的元素再分配。在元素的微观分布中也有证据表明，这些碎屑随后受到了不同程度的蚀变的影响，蚀变是在金属-硅酸盐混合时由涉及本地硅酸盐和外部来源的还原剂（如磷，来源于中陨铁金属）的氧化还原反应引起的。此外，我们的研究结果表明，在不同的碎屑记录的氧化还原反应的不同程度的蚀变最有可能促进不同程度的加热诱导的重熔过程中的金属硅酸盐混合事件。在考虑这些岩浆后次生作用的影响后，通过对玄武质和斜方辉石质碎屑矿物中微量元素含量和分布分别与非堆晶钙长岩和闪长岩矿物中微量元素含量和分布的比较，表明原生岩浆成因，包括母岩浆和源区成分，的Vaca Muerta硅酸盐类似于Howardite-Eucrite-Diogenite（HED）协会的无球粒陨石。两个玄武岩（卵石16和4679）和两个斜方辉石（4659和4670）碎屑的内部53 Mn-53 Cr等时线表明，铬同位素平衡在每个碎屑。然而，正如非堆积的钙长岩和闪长岩一样，玄武质碎屑岩全岩样品中的53 Cr过量值（卵石16中为1.01 ε; 4679中为1.07 ε）显著高于富斜方辉石碎屑岩（4659中为0.62 ε; 4670中为0.53 ε）。在HED母体的情况下，这表明，锰/铬分馏的Vaca Muerta硅酸盐碎屑的母体发生在太阳系的历史非常早，当53 Mn仍然存在。然而，Vaca Muerta碎屑的全岩样品所确定的53 Mn-53 Cr等时线的斜率（对应于3.3 ± 0.6 × 10−6的53 Mn/55 Mn比值）明显低于HED全岩样品所定义的值（对应于4.7 ± 0.5 × 10 - 6的53 Mn/55 Mn比率），表明全球Mn/在HED上发生了类似的事件之后，在Vaca Muerta硅酸盐碎屑的母体上建立了地幔源储层的Cr分馏事件发生了2.2Ma母体
We report here the results of a study of trace element microdistributions and53Mn-53Cr systematics in several basaltic and orthopyroxenitic clasts from the Vaca Muerta mesosiderite. Ion microprobe analyses of selected trace and minor element abundances in minerals of the silicate clasts indicate that, following igneous crystallization, these clasts underwent extensive metamorphic equilibration that resulted in intra- and inter-grain redistribution of elements. There is also evidence in the elemental microdistributions that these clasts were subsequently affected to varying degrees by alteration resulting from redox reactions involving the indigenous silicates and externally derived reducing agents (such as phosphorus, derived from the mesosiderite metal) at the time of metal-silicate mixing. Furthermore, our results suggest that the varying degrees of alteration by redox reactions recorded in the different clasts were most likely facilitated by different degrees of remelting induced by heating during the metal-silicate mixing event. After taking into account the effects of these postmagmatic secondary processes, comparison of the trace and minor element concentrations and distributions in minerals of basaltic and orthopyroxenitic clasts with those of noncumulate eucrites and diogenites, respectively, suggests that the primary igneous petrogenesis, including parent magma and source compositions, of Vaca Muerta silicates were similar to those of achondritic meteorites of the Howardite-Eucrite-Diogenite (HED) association. Internal53Mn-53Cr isochrons obtained for two basaltic (pebble 16 and 4679) and two orthopyroxenitic (4659 and 4670) clasts show that chromium isotopes are equilibrated within each clast. Nevertheless, just as for noncumulate eucrites and diogenites,53Cr excesses in whole-rock samples of the basaltic clasts (∼1.01 ε in pebble 16; ∼1.07 ε in 4679) are significantly higher than in the orthopyroxene-rich clasts (∼0.62 ε in 4659; ∼0.53 ε in 4670). As in the case of the HED parent body, this suggests that Mn/Cr fractionation in the parent body of the Vaca Muerta silicate clasts occurred very early in the history of the solar system, when53Mn was still extant. However, the slope of the53Mn-53Cr isochron defined by the whole-rock samples of Vaca Muerta clasts (corresponding to a53Mn/55Mn ratio of 3.3 ± 0.6 × 10−6) is distinctly lower than that defined by the HED whole-rock samples (corresponding to a53Mn/55Mn ratio of 4.7 ± 0.5 × 10−6), indicating that the global Mn/Cr fractionation event that established mantle source reservoirs on the parent body of the Vaca Muerta silicate clasts occurred ∼2 Ma after a similar event on the HED parent body.
影响因子：
64.8
作者：
Kleine, T;Münker, C;Palme, H
通讯作者：
Palme, H
K. Tomeoka：“Yamamoto-791717 CO 碳质球粒陨石中富含 Na 的 Ca-Al 包裹体”陨石学。
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