Aqueous alteration in the Kaba CV3 carbonaceous chondrite
Aqueous alteration in the Kaba CV3 carbonaceous chondrite
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Kaba CV3 碳质球粒陨石中的水蚀变
DOI：
10.1016/0016-7037(90)90274-o
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发表时间：
1989
影响因子：
5
通讯作者：
P. Buseck
中科院分区：
文献类型：
--
作者：
L. Keller;P. Buseck
卡巴CV3碳质球粒陨石经历了普遍的水蚀变作用，形成了球粒和基质中的含铁皂石。球粒陨石中的皂石颗粒粗大，呈晶体取向关系，使皂石的c∗与顽辉石的∗平行。基质皂石表现出各种结构，包括粗粒和细粒簇，孤立的包体，以及稀疏的富铁橄榄石的片层置换。粗粒团簇可能来自风化层园艺过程中破碎的蚀变球粒。在基质硅酸盐部分溶解过程中释放的物质形成的细粒团簇和孤立的分组。许多皂石与亚微米级Fe-Ni硫化物共生，表明水蚀变过程中没有发生氧化作用。我们认为，由于皂石在整个样品中都存在，因此蚀变发生在卡巴母体之后。通过与陆地赋存状态的类比，卡巴的皂石可能形成于低温(<；100°C)。卡巴地区皂石的分布是由局部块体成分决定的，球粒陨石中的顽辉石比基质中的细粒橄榄石变化范围更大。卡巴的蚀变产物类似于其他水蚀变的碳质球粒陨石，如Mokoia CV3球粒陨石和某些CI球粒陨石。然而，两者之间存在着显著的差异。Kaba缺乏来自莫科亚的球粒陨石和Cais中丰富的高铝层状硅酸盐；Kaba也缺乏在Orgueil发现的蛇纹石和铁水石。卡巴基质中的蚀变产物与CO3球粒陨石中的蚀变产物不同，尽管它们的蚀变前矿物组成相似，这一观察结果可能反映了蚀变过程中不同的温度。
The Kaba CV3 carbonaceous chondrite has undergone pervasive aqueous alteration that produced Fe-bearing saponite in chondrules and matrix. Saponite in chondrules is coarse grained and shows a crystallographic orientation relationship such that c∗ of saponite parallels a∗ of enstatite. Matrix saponite exhibits a variety of textures including coarse-and fine-grained clusters, isolated packets, and sparse, lamellar replacements of Fe-rich olivine. The coarse-grained clusters were probably derived from altered chondrules that were fragmented during regolith gardening. The fine-grained clusters and isolated packets formed from material released during the partial dissolution of matrix silicates. Much saponite is associated with submicron Fe-Ni sulfides, suggesting that conditions were not oxidizing during aqueous alteration. We believe that the alteration occurred after accretion and on the Kaba parent body because saponite is present throughout the sample. By analogy to terrestrial occurrences, the saponite in Kaba probably formed at low temperatures (< 100° C). The distribution of saponite in Kaba is determined by local bulk compositions; enstatite in chondrules has been altered more extensively than the fine-grained olivine in matrix. The alteration products in Kaba resemble those in other aqueously altered carbonaceous chondrites such as the Mokoia CV3 chondrite and in certain CI chondrites. There are, however, significant differences. Kaba lacks the abundant high-Al phyllosilicates in chondrules and in CAIs reported from Mokoia; also lacking in Kaba is the serpentine and ferrihydrite found in Orgueil. Alteration products in Kaba matrix are dissimilar from those in CO3 chondrites even though their prealteration mineralogies were similar, an observation that probably reflects different temperatures during alteration.