Mechanisms of weathering of meteorites recovered from hot and cold deserts and the formation of phyllosilicates
Mechanisms of weathering of meteorites recovered from hot and cold deserts and the formation of phyllosilicates
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DOI：
10.1016/s0016-7037(03)00486-1
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发表时间：
2004-02-01
影响因子：
5
通讯作者：
Bland, PA
中科院分区：
文献类型：
--
作者：
Lee, MR;Bland, PA
从“热”沙漠和南极洲收集的自然风化平衡的普通方解石的岩相学、矿物学和化学分析揭示了两种环境之间风化的惊人相似性和显著差异。在所有研究的陨石中，陆地风化主要是由Fe，Ni金属的氧化和水化作用，产生Fe氧化物和氢氧化物，这些氧化物和氢氧化物部分取代了金属颗粒，并堵塞了原生粒间孔隙，形成矿脉。陨硫铁在“炎热”的沙漠环境中很容易风化，但在南极条件下几乎不发生变化。在这两种环境中，到大约15 - 25%的初始Fe-0和Fe 2+被氧化成Fe 3+时，普通方解石的大部分原生孔隙已被封闭。模拟原生矿物蚀变到一系列风化产物后的体积变化的结果表明，大多数陨石的原生孔隙度足以容纳风化产物。原生孔隙的扩张和角砾化，这已经在一些陨石的部分观察到，只会发生在陨石是特别富含金属，或具有低的原生孔隙度。这些风化产物是缺席最近的福尔斯，但已形成在一个秋天后，类似于100年的博物馆storage. Cl-轴承akaganeite和hibbingite是常见的风化产物在南极发现，但出现在丰富的只有一个'热'沙漠陨石，Daraj 014。大多数富铁陨石风化产物从这两种环境中含有低，但可变浓度的硅，镁和钙。在大多数陨石中，这些元素的一部分被推断为存在于一种非常精细的晶体矿物中，具有类似于1.0 nm的晶格条纹间距;在粒内裂隙中，这种矿物与橄榄石和斜方辉石有拓扑关系。在南极发现的严重风化的ALHA 78045和77002中，硅集中在一种富含铁的层状硅酸盐中。一种未鉴定的含水Si-Fe-Ni-Mg矿物或凝胶也部分取代了ALHA 78045中的Taenite。除了富含铁的风化产物外，“热”沙漠陨石还含有硫酸盐、碳酸钙和二氧化硅，而这些矿物在南极发现中基本上不存在。南极陨石中硅酸盐风化产物的丰度是出乎意料的，表明橄榄石和辉石在这些环境中经历了显着的化学风化。由于在CM 2碳质陨石中含有丰富的地前钙钛矿，南极环境可能是原始陨石小行星母体中水蚀变的有力模拟。版权所有（C）2004 Elsevier Ltd.
Petrographic, mineralogical and chemical analysis of naturally weathered equilibrated ordinary chondrites collected from 'hot' deserts and Antarctica has revealed striking similarities and also pronounced differences in weathering between the two environments. Terrestrial weathering in all meteorites studied is dominated by oxidation and hydration of Fe,Ni metal, producing Fe-oxides and oxyhydroxides that have partially replaced the metal grains and have also occluded primary intergranular pores to form veins. Troilite weathers readily in 'hot' desert environments but undergoes very little alteration under Antarctic conditions. Most of the primary porosity of ordinary chondrites has been occluded by the time that similar to15 to 25% of the initial Fe-0 and Fe2+ has been oxidised to Fe3+ in both environments. Results from modelling the volume changes upon alteration of primary minerals to a range of weathering products demonstrates that the primary porosity of most meteorites is sufficient to accommodate weathering products. Dilation of primary pores and brecciation, which has been observed in parts of some meteorites, will only occur if the meteorite is especially metal-rich, or has a low primary porosity. These weathering products are absent from recent falls but have formed in a fall after similar to100 yr of museum storage.Cl-bearing akaganeite and hibbingite are common weathering products in Antarctic finds but occur in abundance in only one 'hot' desert meteorite, Daraj 014. The majority of Fe-rich weathering products in meteorites from both environments contain low, but variable concentrations of Si, Mg and Ca. In most meteorites a proportion of these elements are inferred to be present as a very finely crystalline mineral with a similar to1.0-nm lattice fringe spacing; where seen within intragranular fractures this mineral has a topotactic relationship with olivine and orthopyroxene. In the heavily-weathered Antarctic finds ALHA 78045 and 77002, Si is concentrated in cronstedtite, a Fe-rich phyllosilicate. An unidentified hydrous Si-Fe-Ni-Mg mineral or gel has also partially replaced taenite in ALHA 78045. In addition to Fe-rich weathering products, 'hot' desert meteorites contain sulphates, Ca-carbonate and silica, whereas such minerals are largely absent from Antarctic finds. The abundance of silicate weathering products in Antarctic meteorites is unexpected and indicates that olivine and pyroxene undergo significant chemical weathering in these environments. As preterrestrial cronstedtite is abundant in CM2 carbonaceous chondrites, the Antarctic environment may be a powerful analog for aqueous alteration in the asteroidal parent bodies of primitive meteorites. Copyright (C) 2004 Elsevier Ltd.