Sur La Cristallinité De l'ILLITE Dans La Diagenèse Et l'ANCHIMÉTAMORPHISME

Segonzac, G; Ferrero, J.; Kübler, Bernard

doi:10.1111/j.1365-3091.1968.tb01105.x

Cited by 38 publications

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“…Mite crystallinity is a parameter sufficiently sensitive to give evidence of metamorphic recrystallizations well before classical petrographic analysis, as shown by WEAVER (1960, 1961). This technique was applied to the Jurassic "terres noires" of the Alps ( DUNOVER DE SEGONZAC et al, 1966; DUNOVER DE SEGONZAC, 1969), the northern Pyrenees (KUBLER, 1966) and the Paleozoic of northern France (DUNOYER DE SECONZAC et al, 1968). The use of statistical Crystallinity measurements is thus a certain index of the zone of thermal influence of metamorphism.…”

Section: Closing Of the Layers: Illite Crystallinitymentioning

confidence: 99%

The Transformation of Clay Minerals During Diagenesis and Low‐grade Metamorphism: A Review

Segonzac¹

1970

Sedimentology

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339

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Summary The results obtained by the author in the study of clay‐minerals diagenesis are compared critically with the principal publications in this field, giving a general picture of the transformation of sheet silicates. Kaolinite minerals are related to the surficial zones of the earth's crust where they are formed. They are characterized by the hexacoordination of aluminium. They furnish paleogeographic indications in ancient sediments. During diagenesis they are very sensitive to the geochemical environment, stable in acid conditions, unstable in alkaline conditions. However, the increase in temperature by burial causes their destruction sooner or later. In the transitional zone to metamorphism (anchizone), kaolinite is not present. Only dickite and nacrite can be observed, provided that the environment is acid. Montmorillonites are hydrated minerals. The rise in temperature and above all in pressure during burial expels water from the interlayers. Concentrated interstitial solutions of diagenesis provide cations which replace molecules of water between the layers. It is an irreversible reaction which produces 14‐Å minerals (chlorites) or 10‐Å minerals (illites), passing generally through mixed‐layer structures. The lack of montmorillonite is normal in formations which have undergone a marked burial. Mixed‐layers are intermediate stages which occur during degradation by weathering and during aggradation by deep diagenesis. This aggradation is the result of an incorporation of certain cations taken up from interstitial solutions, and of a rearrangement within the lattice. There are two major pathways: a potassium and sodium pathway, which produces the illites, then the micas, passing possibly by regular mixed‐layering of the allevardite‐rectorite type; and a magnesium pathway, which produces the chlorites, passing possibly by a regular mixed‐layering of the corrensite type. These mixed‐layers can remain stable until the border of meta‐morphism (anchizone). Micaceous clay minerals or illites form a very heterogenous group in the sediments which have been hardly diagenetized. Particles of diverse origin are found. They become more regular during burial. In deep diagenesis and the anchizone, crystallo‐graphic parameters of the illite are sufficiently well defined to serve as a scale of recrystallization, a zoneographic index. The morphology of the particles changes. Polymorphic types 1Md and 1M are replaced by the 2M‐type. The sharpness of the 10‐Å peak, conventionally called “crystallinity”, is an interesting quantitative criterium, together with the intensity ratio of the 5‐Å and 10‐Å peaks, which is related to the chemical composition of the octahedral layer. Micas in low‐grade metamorphism, called sericites by petrographers, replace the illites discussed above. They are different from the true micas by a weaker layer charge, less than 0.9 by half‐cell. They often contain sodium (paragonitic muscovites and paragonites). The octahedral charge (zero for the muscovite) is generally high, due to the replacement of...

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Section: Closing Of the Layers: Illite Crystallinitymentioning

confidence: 99%

The Transformation of Clay Minerals During Diagenesis and Low‐grade Metamorphism: A Review

Segonzac¹

1970

Sedimentology

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339

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“…The 187 (001) reflection of sedimentary illite is considered a sensitive indicator of the relative severity of incipient metamorphism, provided the magnesium/aluminum ratio of the illite is not too high (Esquevin, 1969). A relatively broad (001) peak for illite may indicate poor "crystallinity', small crystal size, interlayer hydration, variation in the nature of the interlayer cations, and interstratification with other clay minerals such as montmorillonite or montmorillonite + chlorite (Weaver, 1961;Kubler, 1968;De Segonzac et al, 1968;McKirdy, 1974;Brown, 1961;Grim, 1968). Sharpening of the (001) peak with the onset of metamorphism is presumably caused by dehydration and collapse of expanded layers as well as crystal growth and improved "crystallinity" (Weaver, 1961).…”

Section: Introductionmentioning

confidence: 99%

“…Attention was focused on illite, because a number of workers have observed that within the zone of incipient metamorphism, or "anchimetamorphism", (the transition zone between diagenesis and metamorphism) the breadth of the (001) diffraction peak of this mineral decreases progressively as the degree of metamorphism increases (Weaver, 1961;Kubler, 1968;De Segonzac et al, 1968;McKirdy, 1974). The 187 (001) reflection of sedimentary illite is considered a sensitive indicator of the relative severity of incipient metamorphism, provided the magnesium/aluminum ratio of the illite is not too high (Esquevin, 1969).…”

Section: Introductionmentioning

confidence: 99%

A Relationship Between Crystallographic Properties of Illite and Chemical Properties of Extractable Organic Matter in Pre-Phanerozoic and Phanerozoic Sediments

Jackson¹

1977

Clays and clay miner.

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Abstrael~Crystallographic properties of illite and chemical properties of organic matter in various mudstones ranging in age from Archean to Miocene were investigated. The breadth of the (001) X-ray powder diffraction peak of illite correlates significantly with the ratio of aliphatic to condensed.-aromatic components and the degree of condensation of aromatic rings of the polar ("humic') fraction of extractable bituminous organic matter. The broader the diffraction peak, the less highly condensed and aromatic (i.e. less highly humified) is the organic matter associated with the illite. Breadth of illite diffraction peak and degree of humification of polar organic matter vary in a complex and apparently systematic way through geologic time. All of the three different suites of mudstones investigated ("calcareous," "non-calcareous," and "glacial" mudstones) gave similar patterns of secular variation. In addition, the ratio of diffraction intensities for the (002) and (001) reflections (loo2/lool) of illite in calcareous mudstones and limestones showed a strong negative correlation with geologic age, indicating that the illites in the older rocks are enriched in magnesium with respect to aluminum.The correlation between crystal structure of illite and degree of humification of its associated organic matter could, by itself, be interpreted as an effect of post-depositional maturation processes, whereby "crystallinity" and degree of humification both increased as functions of heat and pressure. However, the patterns of secular variation suggest that the observed variations are primary, or were pre-determined by primary characteristics of the sample materials. The possibility that the original structure and composition of the organic matter influenced post-depositional changes in the crystallographic properties of sedimentary clay minerals, or post-depositional genesis of clay, would seem to merit consideration. The demonstrated relationship between crystallographic properties of iUite and the nature of the "humic" matter constitutes evidence that most of the extractable organic matter is truly indigenous to the rock in which it occurs. The results also imply that molecular structure of extractable organic matter can be used in place of the breadth of the (001) diffraction peak of illite as an index of incipient metamorphism within a single formation or stratigraphic sequence, provided the primary characteristics of the organic matter are nearly the same in all samples. This method would have the advantage of being applicable to all sediments, not just those containing illite (specifically, aluminum-rich illite).The secular variation of the Ioo2/Iool ratio of illite in calcareous sediments is provisionally ascribed to diagenetic processes whereby magnesium is abstracted from pore water and groundwater and is gradually assimilated into the crystal structure.

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Diagenetic Reactions in Clays

Velde

1983

Sediment Diagenesis

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Sur La Cristallinité De l'ILLITE Dans La Diagenèse Et l'ANCHIMÉTAMORPHISME

Cited by 38 publications

References 1 publication

The Transformation of Clay Minerals During Diagenesis and Low‐grade Metamorphism: A Review

The Transformation of Clay Minerals During Diagenesis and Low‐grade Metamorphism: A Review

A Relationship Between Crystallographic Properties of Illite and Chemical Properties of Extractable Organic Matter in Pre-Phanerozoic and Phanerozoic Sediments

Diagenetic Reactions in Clays

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