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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Aqueous alteration of opaque assemblages in the Ningqiang carbonaceous chondrite: Evidence from oxygen isotopes
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Aqueous alteration of opaque assemblages in the Ningqiang carbonaceous chondrite: Evidence from oxygen isotopes

机译：宁强碳质球粒陨石中不透明集合体的水蚀变化：氧同位素证据

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摘要

Chondrules and matrix of the Ningqiang carbonaceous chondrite contain numerous opaque assemblages (OAs). These OAs are mainly composed of Ni-rich metal, magnetite, sulfides, phosphates with minor amounts of silicates and trace amounts of Pt-metal grains. Their mineral assemblage is very similar to that of OAs found in Allende refractory inclusions. In this study, we performed in situ analyses of O-isotopic compositions of magnetite and whitlockite in OAs and of olivine adjacent to OAs from Ningqiang. O-isotopic compositions of magnetite vary by 16 parts per thousand in 618 0 and fall on a regression line with a slope of 0.51 and a mean Delta 17O of - 2.9 +/- 0.3 (1 sigma)parts per thousand in the three-O-isotope diagram. Magnetite grains have consistently higher Delta O-17 values than their adjacent olivine grains. The mineral chemistry and O-isotopic compositions of OAs in Ningqiang chondrules and matrix are most consistent with the formation of magnetites and whitlockite by aqueous alteration of preexisting metal alloys within a planetary body. Formation of magnetites and phosphates in OAs thus do not constrain processes in the early solar nebula, but rather provide information on metamorphism in a planetary environment. (c) 2006 Elsevier B.V. All rights reserved.
机译：宁强碳质球粒陨石的球状体和基质含有许多不透明的集合体（OAs）。这些OA主要由富镍金属，磁铁矿，硫化物，磷酸盐，少量的硅酸盐和痕量的Pt金属晶粒组成。它们的矿物组成与阿连德耐火夹杂物中发现的OA非常相似。在这项研究中，我们对宁强地区的OAs和与OAs相邻的橄榄石中的磁铁矿和菱镁矿O同位素组成进行了原位分析。磁铁矿的O同位素组成在618 0中变化为千分之十六，并落在回归线上，斜率为0.51，而在三个O中，平均Delta 17O为千分之2.9-+/- 0.3（1 sigma）。 -同位素图。磁铁矿晶粒始终比相邻的橄榄石晶粒具有更高的Delta O-17值。宁强软骨和基体中OAs的矿物化学和O同位素组成与行星体内先有金属合金的水蚀改变最符合磁铁矿和辉锰矿的形成。因此，OAs中磁铁矿和磷酸盐的形成并不限制早期太阳星云的过程，而是提供有关行星环境中变质作用的信息。 （c）2006 Elsevier B.V.保留所有权利。

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