Topaz-bearing Lower Ordovician orthogneiss within the Ostrong Nappe System – The Laimbach Orthogneiss (Bohemian Massif, Lower Austria)

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F67985831%3A_____%2F24%3A00586148" target="_blank" >RIV/67985831:_____/24:00586148 - isvavai.cz</a>

Výsledek na webu

<a href="https://link.springer.com/article/10.1007/s00531-024-02412-y" target="_blank" >https://link.springer.com/article/10.1007/s00531-024-02412-y</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.17738/ajes.2024.0003" target="_blank" >10.17738/ajes.2024.0003</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Topaz-bearing Lower Ordovician orthogneiss within the Ostrong Nappe System – The Laimbach Orthogneiss (Bohemian Massif, Lower Austria)

Popis výsledku v původním jazyce

In the 1980s, large parts of the Bohemian Massif in Austria were explored for the occurrence of raw materials (Göd, 1988), and a trace content of topaz was discovered in channels draining the eastern slope of the Ostrong (Lower Austria). Orthogneiss bodies in the Ostrong Nappe System are shown to be the source of these topaz occurrences, and Raman spectroscopy indicates that topaz is fluorine rich. So far, this is the only occurrence of topaz-bearing orthogneiss within the entire Moldanubian Superunit. The orthogneiss shows a tectonic overprint and exhibits a weak to well-developed foliation, as well as local folding. Samples taken near the tectonic boundary of the Ostrong to the Drosendorf Nappe Systems show stronger shear deformation with a pronounced mylonitic foliation and stretching lineation. Detailed geo-chemical investigations of the major and trace elements indicate a classification as S-type granite with a high degree of differentiation and a peraluminous character. The orthogneiss has a high SiO2 content of 72.8–77.3 wt%, as well as a noteworthy high fluorine content of up to 2760 ppm. Mineral compositions show zoned plagioclase with an albite component of about 87–99 mol%, increasing towards the grain margin. Garnet occurs rarely, but consistently in those samples near the tectonic boundary of the Ostrong- to the Drosendorf Nappe Systems. Garnet is almandine-dominated, shows no zoning and is single-phased. Sillimanite is common and samples near the tectonic boundary also contain kyanite. To determine the previously unknown protolith age of the orthogneiss, U-Pb zircon dating was applied. Three zircon fractions from two samples yield concordia ages of 475.3 ± 1.0 Ma, 474.8 ± 2.9 Ma, and 473.5 ± 1.5 Ma, identical in assigned uncertainties, reflecting magmatic zircon growth. Furthermore, the short prismatic habit of zircon grains indicates a plutonic rather than volcanic origin of the protolith. Dating results also provide a minimum sedimentation age for the rocks of the Ostrong Nappe System within Austria. In comparison with other metagranitoids and orthogneisses of the Moldanubian Nappes, the investigated orthogneiss shows strong similarities with the Gföhl Gneiss and the Moldanubian Granulite. The orthogneiss therefore is considered as a more fractionated equivalent of the Gföhl Gneiss. In conclusion we suggest to name the studied orthogneiss Laimbach Orthogneiss in the rank of a lithodeme (NACSN, 2005), after the locality Laimbach am Ostrong (48°19′01″N, 15°07′19″E), which is located centrally with respect to the occurrences of this gneiss.n

Název v anglickém jazyce

Topaz-bearing Lower Ordovician orthogneiss within the Ostrong Nappe System – The Laimbach Orthogneiss (Bohemian Massif, Lower Austria)

Popis výsledku anglicky

In the 1980s, large parts of the Bohemian Massif in Austria were explored for the occurrence of raw materials (Göd, 1988), and a trace content of topaz was discovered in channels draining the eastern slope of the Ostrong (Lower Austria). Orthogneiss bodies in the Ostrong Nappe System are shown to be the source of these topaz occurrences, and Raman spectroscopy indicates that topaz is fluorine rich. So far, this is the only occurrence of topaz-bearing orthogneiss within the entire Moldanubian Superunit. The orthogneiss shows a tectonic overprint and exhibits a weak to well-developed foliation, as well as local folding. Samples taken near the tectonic boundary of the Ostrong to the Drosendorf Nappe Systems show stronger shear deformation with a pronounced mylonitic foliation and stretching lineation. Detailed geo-chemical investigations of the major and trace elements indicate a classification as S-type granite with a high degree of differentiation and a peraluminous character. The orthogneiss has a high SiO2 content of 72.8–77.3 wt%, as well as a noteworthy high fluorine content of up to 2760 ppm. Mineral compositions show zoned plagioclase with an albite component of about 87–99 mol%, increasing towards the grain margin. Garnet occurs rarely, but consistently in those samples near the tectonic boundary of the Ostrong- to the Drosendorf Nappe Systems. Garnet is almandine-dominated, shows no zoning and is single-phased. Sillimanite is common and samples near the tectonic boundary also contain kyanite. To determine the previously unknown protolith age of the orthogneiss, U-Pb zircon dating was applied. Three zircon fractions from two samples yield concordia ages of 475.3 ± 1.0 Ma, 474.8 ± 2.9 Ma, and 473.5 ± 1.5 Ma, identical in assigned uncertainties, reflecting magmatic zircon growth. Furthermore, the short prismatic habit of zircon grains indicates a plutonic rather than volcanic origin of the protolith. Dating results also provide a minimum sedimentation age for the rocks of the Ostrong Nappe System within Austria. In comparison with other metagranitoids and orthogneisses of the Moldanubian Nappes, the investigated orthogneiss shows strong similarities with the Gföhl Gneiss and the Moldanubian Granulite. The orthogneiss therefore is considered as a more fractionated equivalent of the Gföhl Gneiss. In conclusion we suggest to name the studied orthogneiss Laimbach Orthogneiss in the rank of a lithodeme (NACSN, 2005), after the locality Laimbach am Ostrong (48°19′01″N, 15°07′19″E), which is located centrally with respect to the occurrences of this gneiss.n

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10504 - Mineralogy

Projekt

—

Návaznosti

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Rok uplatnění

2024

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Název periodika

Austrian Journal of Earth Sciences

ISSN

2072-7151

e-ISSN

2072-7151

Svazek periodika

117

Číslo periodika v rámci svazku

1

Stát vydavatele periodika

PL - Polská republika

Počet stran výsledku

20

Strana od-do

25-44

Kód UT WoS článku

001175228900001

EID výsledku v databázi Scopus

2-s2.0-85188999586