Replacement of glass in the Nakhla meteorite by berthierine: Implications for understanding the origins of aluminum-rich phyllosilicates on Mars
Replacement of glass in the Nakhla meteorite by berthierine: Implications for understanding the origins of aluminum-rich phyllosilicates on Mars
复制标题
DOI：
10.1111/maps.12687
复制
发表时间：
2016-09-01
影响因子：
2.2
通讯作者：
Chatzitheodoridis, Elias
中科院分区：
文献类型：
--
作者：
Lee, Martin R.;Chatzitheodoridis, Elias
通过扫描和透射电子显微镜对来自火星陨石Nakhla的熔融包裹体中的铝硅酸盐玻璃进行研究，发现它们已被berthierine（一种铝铁蛇形矿物）所取代。这种蚀变反应是由液态水介导的，液态水沿着封闭的奥辉石和橄榄石颗粒的裂缝进入玻璃。水岩比较低，水溶液呈环中性和还原性。他们引进了从橄榄石的溶解中提取的镁和铁，并出口了碱。用x射线显微分析和电子衍射鉴定了柏硫莲。它的出现局限于熔体包裹体中原来是玻璃的部分，这表明在环境物理化学条件下，铝和硅的迁移率很低。蛇纹岩的发现增加了纳赫拉岩浆期后含水硅酸盐的种类，包括皂石和蛋白石a。次生硅酸盐的多样性表明，在水蚀变过程中，亚毫米尺度上发育了不同成分的微环境。Nakhla的berthierine的稀缺性与火星地壳的轨道遥感结果一致，显示富铝层状硅酸盐的丰度非常低。
A scanning and transmission electron microscope study of aluminosilicate glasses within melt inclusions from the Martian meteorite Nakhla shows that they have been replaced by berthierine, an aluminum-iron serpentine mineral. This alteration reaction was mediated by liquid water that gained access to the glasses along fractures within enclosing augite and olivine grains. Water/rock ratios were low, and the aqueous solutions were circumneutral and reducing. They introduced magnesium and iron that were sourced from the dissolution of olivine, and exported alkalis. Berthierine was identified using X-ray microanalysis and electron diffraction. It is restricted in its occurrence to parts of the melt inclusions that were formerly glass, thus showing that under the ambient physico-chemical conditions, the mobility of aluminum and silicon were low. This discovery of serpentine adds to the suite of postmagmatic hydrous silicates in Nakhla that include saponite and opal-A. Such a variety of secondary silicates indicates that during aqueous alteration compositionally distinct microenvironments developed on sub-millimeter length scales. The scarcity of berthierine in Nakhla is consistent with results from orbital remote sensing of the Martian crust showing very low abundances of aluminum-rich phyllosilicates.