Clay-mineraloid weathering products in Antarctic meteorites
Clay-mineraloid weathering products in Antarctic meteorites
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南极陨石中的粘土矿物风化产物
DOI：
10.1016/0016-7037(86)90076-1
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发表时间：
1986
影响因子：
5
通讯作者：
J. Gooding
中科院分区：
文献类型：
--
作者：
J. Gooding
粘土类矿物与石膏、钾铁硫酸盐（可能是黄钾铁矾）、隐晶质铁锈有关，也可能与沸石和/或（次生）碱长石有关，作为来自南极洲维多利亚地艾伦山 (ALH) 和象冰碛 (EET) 收集区的石陨石中的陆地风化产物。风化在锂辉石 EETA79004 和 EETA79005、闪长岩 ALHA77256 和 EETA79002、镁橄榄石 EETA79001 和 H5-球粒陨石 ALH82102 的熔壳中以及无球粒陨石内部样品中玻璃和斜长石的分解产物中形成裂缝充填物。粘土类矿物表现出块状到早期蠕虫状的形式，其元素组成表明类似蒙皂石和云母相。尽管大块样品的 X 射线衍射法和差示扫描量热法表明粘土矿物没有很好地结晶，但沉积物太小，无法产生用于相鉴定的纯材料。以蒙皂石为基础计算的典型结构式如下： (K0.26,Ca0.04(Al0.97,Ti0.02,Fe3+0.77,Mg0.03)Si4.00O10(OH)2·n2O 净电荷：-0.28；过量：0.58 Si、0.02 Cl、0.09 SO4、0.02 PO4。 “氢低温” 即使液态水供应有限，成岩作用也能在 104-106 年的时间尺度上启动粘土矿物的形成。宇宙化学家必须注意不要将南极陨石样本中可能由风化引起的元素和同位素分馏与地球前“宇宙”过程的特征相混淆。然而，如果进行适当的样品选择和测试，粘土矿物和其他物质的出现 风化产物可能不会阻碍南极陨石研究的进展。
Clay mineraloids are associated with gypsum, K-Fe-sulfates (possibly jarosite), cryptocrystalline rust, and possibly with zeolites and/or (secondary) alkali feldspars as terrestrial weathering products in stony meteorites from the Allan Hills (ALH) and Elephant Moraine (EET) collection areas in Victoria Land, Antarctica. Weathering formed fracture fillings in fusion crusts of eucrites EETA79004 and EETA79005, diogenites ALHA77256 and EETA79002, shergottite EETA79001 and H5-chondrite ALH82102 and decomposition products of glass and plagioclase in interior samples of achondrites. Clay mineraloids displayed massive to incipient-vermicular forms with elemental compositions that suggest smectite- and mica-like phases. Deposits were too small to yield pure material for phase identification although x-ray diffractometry and differential scanning calorimetry of bulk samples suggested that the clay mineraloids were not well crystallized. A typical structural formula, calculated on a smectite basis, follows: (K0.26,Ca0.04(Al0.97,Ti0.02,Fe3+0.77,Mg0.03)Si4.00O10(OH)2·n2O Net charge:-0.28; Excessions: 0.58 Si, 0.02 Cl, 0.09 SO4,0.02 PO4. “Hydrocryogenic” diagenesis can initiate clay-mineral formation on timescales of 104-106y even with only limited supplies of liquid water.Cosmochemists must take care not to confuse possible weathering-induced elemental and isotopic fractionations in Antarctic meteorite samples with signatures of pre-terrestrial “cosmic” processes. Given proper sample selection and testing, though, occurrence of clay-mineraloid and other weathering products should probably not impede progress in studies of Antarctic meteorites.