Illite ‘crystallinity’, maturation of organic matter and microstructural development associated with lowest-grade metamorphism of Neoproterozoic sediments in the Teplá-Barrandian unit, Czech Republic
| Autor: | J. Filip, K. Melka, V. Suchý, Ivana Sýkorová, Vladimír Machovič |
|---|---|
| Rok vydání: | 2007 |
| Předmět: |
Proterozoic
Metamorphic rock Geochemistry Metamorphism 020101 civil engineering 02 engineering and technology engineering.material 010502 geochemistry & geophysics 01 natural sciences 0201 civil engineering Illite crystallinity Geochemistry and Petrology Illite Alpine orogeny engineering Cleavage (geology) Paragenesis Geology 0105 earth and related environmental sciences |
| Zdroj: | Clay Minerals. 42:503-526 |
| ISSN: | 1471-8030 0009-8558 |
| DOI: | 10.1180/claymin.2007.042.4.08 |
| Popis: | Metamorphic grade, palaeothermal history and the influence of tectonic strain on clay minerals and organic matter transformation were studied in the eastern part of the Teplá-Barrandian unit in the Czech Republic. The metamorphic grade of pelitic sediments ranges from the lower anchizone (IC ~0.30–0.36Δº2θ) to the lowermost epizone (IC ~0.24–0.26Δº2θ). Increase in metamorphic grade is paralleled by the development of anastomosing cleavage and lenticular quartz grains in the anchizone which give way to slaty cleavage and dynamically recrystallized ribbon quartz grains in the lower epizone. White mica in highly strained rocks generally has greater IC values whereas chlorite displays reduced values in deformed and cleaved samples. The organic matter dispersed in the sediments represents a complex assemblage of highly matured particles of uncertain origin, pyrobitumen and ‘transitional matter’. The reflectance of organic fragments generally varies from 3.1% to 7.7% ofRmaxwhich suggests anthracite to meta-anthracite rank progrades to semigraphite in higher-grade samples, although the overall link betweenRmaxand IC values is weak, if present at all. Newly formed shear-induced graphite appears abruptly near the anchizone-epizone boundary and correlates with the onset of plastic deformation and dynamic recrystallization of quartz grains in the host sediments.Maximum metamorphic temperatures within the Neoproterozoic sequence in the range of 250–350ºC were attained during the Cadomian (Pan-African) orogeny at 540–550 Ma. Apatite fission-track analysis reveals a subsequent decrease in rock temperature over the period 340–350 Ma that persisted throughout the late Palaeozoic. The most recent episode of accelerated cooling occurred between 20 and 40 Ma, corresponding with the regional uplift of the Bohemian Massif due to the Alpine orogeny. |
| Databáze: | OpenAIRE |
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