Formation and Processing of Amorphous Silicates in Primitive Carbonaceous Chondrites and Cometary Dust
Formation and Processing of Amorphous Silicates in Primitive Carbonaceous Chondrites and Cometary Dust
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原始碳质球粒陨石和彗星尘中非晶硅酸盐的形成和加工
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发表时间：
2012
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影响因子：
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通讯作者：
S. Messenger
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文献类型：
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作者：
L. Keller;S. Messenger
球粒陨石-多孔星际尘埃颗粒(CP IDP)在亚微米尺度上表现出强烈的非均质性和不平衡的矿物学特征，富含碳、氮和挥发性微量元素，并含有丰富的极前物质[1-4]。这些观察表明，CP IDPs在很大程度上逃脱了严重改变或破坏原始陨石原始矿物学的热加工和水-岩相互作用。CP IDPs被认为代表了太阳系组成部分的直接样本--一种星云和太阳系前物质的复杂混合物，基本上不受二次加工的干扰。Cp IDPs的化学和同位素性质及其进入大气的速度也与彗星的起源相一致。宝石(嵌有金属和硫化物的玻璃)颗粒是CP IDPs的主要硅酸盐成分。宝石颗粒是直径0.5微米的物体，由许多10到50纳米大小的铁镍金属和分散在镁硅铝铁非晶态硅酸盐基质中的铁镍硫化物颗粒组成[2，5]。根据它们的化学和同位素组成，大多数宝石似乎是早期太阳星云的非平衡凝聚物[2]。如果宝石颗粒是一种常见的星云产物，那么它们也应该在物理上最原始的球粒陨石的基质中大量存在。尽管无定形硅酸盐在最原始的陨石中很常见[6-9]，但它们与宝石颗粒的关系以及它们的成分和微结构受到母体处理(氧化和水蚀变)影响的程度很少受到限制。在这里，我们比较和对比了原始碳质球粒陨石中的无定形硅酸盐和国内流离失所者中的宝石颗粒的化学、显微结构和同位素性质。
Chondritic-porous interplanetary dust particles (CP IDPs) exhibit strongly heterogeneous and unequilibrated mineralogy at sub-micron scales, are enriched in carbon, nitrogen and volatile trace elements, and contain abundant presolar materials [1-4]. These observations suggest that CP IDPs have largely escaped the thermal processing and water-rock interactions that have severely modified or destroyed the original mineralogy of primitive meteorites. CP IDPs are believed to represent direct samples of the building blocks of the Solar System - a complex mixture of nebular and presolar materials largely unperturbed by secondary processing. The chemical and isotopic properties of CP IDPs and their atmospheric entry velocities are also consistent with cometary origins. GEMS (glass with embedded metal and sulfides) grains are a major silicate component of CP IDPs. GEMS grains are < 0.5 microns in diameter objects that consist of numerous 10 to 50 nm-sized Fe-Ni metal and Fe-Ni sulfide grains dispersed in a Mg-Si-Al-Fe amorphous silicate matrix [2, 5]. Based on their chemistry and isotopic compositions, most GEMS appear to be non-equilibrium condensates from the early solar nebula [2]. If GEMS grains are a common nebular product, then they should also be abundant in the matrices of the most physically primitive chondritic meteorites. Although amorphous silicates are common in the most primitive meteorites [6-9], their relationship to GEMS grains and the extent to which their compositions and microstructure have been affected by parent body processing (oxidation and aqueous alteration) is poorly constrained. Here we compare and contrast the chemical, microstructural and isotopic properties of amorphous silicates in primitive carbonaceous chondrites to GEMS grains in IDPs.