Illite-smectite structural changes during metamorphism in black Cambrian Alum shales from the Baltic area
-
Holger Lindgreen
,
Victor A. Drits
Abstract
Illite-smectite (I-S) from Cambrian black shale of both early diagenetic and anchimetamorphic grade was investigated to determine the mechanism of the clay transformation. The layer sequences, the distribution of thicknesses of coherent scattering domains (CSDs), and the three-dimensional ordering were determined by X-ray diffraction (XRD). The proportions of cis-vacant (cv) and transvacant (tv) 2:1 layers were determined by thermal analysis and the proportion and distribution of interlayer ammonium by XRD and by infared spectroscopy (IR). The structural formulae were determined from total chemical analysis, and Mössbauer and 27Al NMR spectroscopies, and the particle shape and size investigated by atomic force microscopy (AFM). In the early diagenetic samples, the I-S is composed of two phases, one of which contains 0.05 and the other 0.25 smectite (S) interlayers. The first phase does not change during metamorphism. In the second phase, 0.20 S are converted to tobelite (T) layers through fixation of NH4+, but the I layers are not changed. Simultaneously, the proportion of cv layers changes from 0.18 to 0.02, and the tetrahedral substitution of Al for Si is parallel to the increase in T layers. All I interlayers contain 0.75K per O10(OH)2. Furthermore, the metamorphism results in increasing mean thickness of CSDs from 5.1-6.8 nm for the lowdiagenetic samples to 6.7-8.4 nm for the anchimetamorphic samples. We conclude that the tobelitization was accompanied by transformation of cv to tv 2:1 layers adjacent to the smectite interlayers, and formation of tv layers adjacent to the newformed tobelite interlayers in otherwise intact crystallites. This mechanism only partly resembles the tobelitization previously observed in the Upper Jurassic North Sea oil source rocks. I-S in these rocks contained tv 2:1 layers and T interlayers formed through solid-state Al for Si substitution in the tetrahedral sheet and by ammonium fixation in the corresponding interlayers. These different mechanisms are probably because the North Sea I-S originated from weathered illite, like the Cambrian high-illitic phase, whereas the Cambrian low-illitic phase undergoing the transformation originated from cv smectite of volcanic origin. The results indicate that the illitization in oil source rocks is linked to oil generation, and that it deviates from the illitization in other rocks because of the supply of ammonium formed during oil generation and the fixation of this ammonium in the former smectite interlayers.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Measurement of crystal size distributions
- Pressure dependence of the solubility of Ar and Kr in melts of the system SiO2-NaAlSi2O6
- Solubility behavior of water in haploandesitic melts at high pressure and high temperature
- Proton-containing defects at forsterite {010} tilt grain boundaries and stepped surfaces
- Incorporation of Fe3+ into forsterite and wadsleyite
- Molecular dynamics simulation of Al/Si-ordered plagioclase feldspar
- Cation ordering and structural variations with temperature in MgAl2O4 spinel: An X-ray single-crystal study
- Aluminium coordination in tektites: A XANES study
- Crystal structure of Cr-mullite
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- New insights into the mechanism for chloritization of biotite using polytype analysis
- The dissolution of hectorite: In-situ, real-time observations using atomic force microscopy
- Quantification of minor phases in growth kinetics experiments with powder X-ray diffraction
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- The tremolite-actinolite-ferro–actinolite series: Systematic relationships among cell parameters, composition, optical properties, and habit, and evidence of discontinuities
- Cordierite I: The coordination of Fe2+
- Cordierite II: The role of CO2 and H2O
- Crystal chemical variations in Li- and Fe-rich micas from Pikes Peak batholith (central Colorado)
- The crystal structure of TlAlSiO4: The role of inert pairs in exclusion of Tl from silicate minerals
- The structure of agrinierite: a Sr-containing uranyl oxide hydrate mineral
- The crystal structure of namibite, Cu(BiO)2VO4(OH), and revision of its symmetry
- The crystal structure of pararobertsite and its relationship to mitridatite
- Description and crystal structure of cabalzarite Ca(Mg,Al,Fe)2(AsO4)2(H2O,OH)2, a new mineral of the tsumcorite group
- Tegengrenite, a new, rhombohedral spinel-related Sb mineral from the Jakobsberg Fe-Mn deposit, Värmland, Sweden
