Naslov
Illite crystallinity as indicator of geological processes - three examples

Autori
Uhlík, Peter ; Pelech, Ondrej ; Topalović, Ena ; Tibljaš, Darko & Puškelova, L'ubica

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Environmental, Structural and Stratigraphical Evolution of the Western Carpathians: 12th ESSEWECA Conference, Abstract book / Hudáčkova, Natália, Ruman, Andrej & Šujan, Michal - Bratislava : Comenius University Bratislava, 2022, 154-155

ISBN
978-80-223-5519-3

Skup
12th Conference: Environmental, Structural and Stratigraphical Evolution of the Western Carpathians (ESSEWECA)

Mjesto i datum
Bratislava, Slovačka, 08.12.2022. - 09.12.2022

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
illite, Kübler index, diagenesis, very-low grade metamorphism

Sažetak
The most widely used method of determining grade of transformation in metapelitic sequences is the XRD-based illite crystallinity technique, introduced by Kübler. Kübler index (KI) of illite crystallinity was used to define the anchizone and also defined the prograde limit of diagenesis and the initiation of the epizone. The illite crystallinity technique measures the width of the first basal reflection of dioctahedral illite- muscovite at a spacing of the 10 Å, at half-height above the background (in Δ°2θ ; review in Merriman & Peacor 1999). The contribution will present examples of KI use in three different geological environments. The first set of samples is from NW Croatia, previously considered to be non-metamorphosed. The analyses were performed on the Late Paleozoic black shales belonging to the northwesternmost part of the Internal Dinarides sampled in the Samobor-Žumberak Mountains and the Marija Gorica Hills, and on the Triassic (Upper Ladinian) carbonaceous dolomites belonging to the post- Variscan Alpine overstep sequences of the Tisia Mega-Unit found in the western part of the Papuk Mountain. A total of 7 rock samples, including 3 dolomite samples (two of them rich in organic carbon), were used to measure KI values. XRD analysis of the Late Paleozoic black shales shows a dominance of illite, accompanied by chlorite. The KI values obtained range from 0.33 to 0.36 Δ°2θ, indicating that the black shales underwent anchizonal thermal alteration. The clay minerals in carbonaceous dolomites are illite and kaolinite. The KI values of 0.79 and 0.84 Δ°2θ indicate a diagenetic alteration. The second set of samples from the eastern part of the Strážovské vrchy Mts. represents a more or less typical region of the core mountains of the Western Carpathians. Four siltstoneclaystones and one limestone sample with admixture of siliciclastic compounds are from the cover sequences of Tatricum (from the Triassic to the Cretaceous age). Three of them, with major components of illite and chlorite in clay fraction, identified a high anchizone. Two of them contain mixed-layered illite-smectite that shows only late diagenetic thermal alteration. Lower thermal transformation could be caused by less affected of buried zones by younger tectonics. This set of samples was supplemented by a sample from overlying Fatricum. This sample was also identified as late diagenetic. The third example is located in the Central Slovakia Volcanic Field on the inner side of the Carpathian arc. The samples are from the intermediate-sulphidation precious and base metal deposit Banská Hodruša at the Rozália mine that is hosted by the central zone of a Miocene andesite Štiavnica stratovolcano (Kubač et al. 2018 ; Koděra et al. 2019). The significant presence of illite has been used for determination of temperature conditions and character of fluid that formed wall-rock alterations. KI was used for the calculation of crystallisation temperatures using the data from the recent geothermal area in Taupo, New Zealand (Ji and Browne 2000). At least 50 measurements of KI were done. They show a temperature range from 255 to 315°C, which is in agreement with the data from the study of fluid inclusions within the Banská Hodruša epithermal deposit (Koděra et al. 2019).

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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