Amphibole and pyroxene as indicators of alkaline conditions in banded carbonatite-like marbles from Bližná, Český Krumlov Unit, Moldanubian Zone

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00094862%3A_____%2F21%3AN0000064" target="_blank" >RIV/00094862:_____/21:N0000064 - isvavai.cz</a>

Nalezeny alternativní kódy

RIV/00216224:14310/21:00119494

Výsledek na webu

<a href="http://www.jgeosci.org/detail/jgeosci.336" target="_blank" >http://www.jgeosci.org/detail/jgeosci.336</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.3190/jgeosci.336" target="_blank" >10.3190/jgeosci.336</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Amphibole and pyroxene as indicators of alkaline conditions in banded carbonatite-like marbles from Bližná, Český Krumlov Unit, Moldanubian Zone

Popis výsledku v původním jazyce

Amphiboles and diopside occur in several distinct mineral assemblages in banded carbonatite-like marbles from the Bližná graphite mine, Český Krumlov Unit, Moldanubian Zone. The carbonatite-like marble is interlayered with dominant ordinary metacarbonates as a single continuous stratabound layer, up to 3-4 m thick. It is enriched in elements typical for carbonatites (REE, Y, Th, Sr, Nb, Zr, and Mo) and contains accessory betafite-pyrochlore and uranothorite along with molybdenite, sulfides (e.g., pyrite, pyrrhotite) and oxides (e.g., magnetite, ilmenite). Detailed study of thin sections in optical microscope and BSE images as well as results of EMPA revealed three distinct mineral assemblages - richterite + forsterite (RF) assemblage (Rht + Fo + Cal ˃ Dol ˃ Phl + Di), Na rich actinolite + diopside (AD) assemblage (Di + Act + Rht + Cal ˃ Phl) and magnesio-hastingsite + diopside (HD) assemblage (Mhst + Di + Cal ˃ Ab + Phl). The distinct amphibole species found within the individual assemblages exhibit complex textural relations and crystallized in several prograde and retrograde stages. The following amphibole species were recognized in the individual assemblages: RF - (richterite > ferri-winchite > tremolite, edenite), AD - (actinolite > ferri-winchite; richterite > ferri-katophorite; magnesio-riebeckite), HD - (magnesio-hastingsite; ferri-winchite, actinolite). They differ especially in Mg/(Mg + Fetot) ratio and concentrations of F. Diopside contains up to 17 mol. % of the aegirine component and albite is Fe, Ba-enriched (≥ 0.69 wt. % BaO and ≥ 0.50 wt. % Fe2O3tot). The composition of amphiboles and pyroxenes indicates the alkaline environment of their formation; unusually high Fe2O3 contents in albite plagioclase have known counterparts in alkaline pegmatites and some carbonatite dykes. The following options of potential origin of the carbonatite-like marble from Bližná are discussed: (i) metacarbonates potentially with Na- and Na,Ca-carbonates and sulfate admixture; (ii) admixture of alkaline volcanodetritic component during carbonate sedimentation; (iii) metamorphosed carbonatites enclosed in ordinary sedimentary metacarbonate; (iv) Na-rich metasomatites characterized by mineral assemblages with Na,Fe,F-enriched amphiboles, diopside with high aegirine component and albite. With regard to the observed mineral assemblages, textures and composition of minerals, we can exclude (i) marine evaporates, whereas the other options (ii), (iii) and (iv) are, in general, possible. The amphiboles observed in the Bližná carbonatite-like marble are unique within the Bohemian Massif and distinctly different from amphiboles found in metacarbonates with evaporite component.

Název v anglickém jazyce

Amphibole and pyroxene as indicators of alkaline conditions in banded carbonatite-like marbles from Bližná, Český Krumlov Unit, Moldanubian Zone

Popis výsledku anglicky

Amphiboles and diopside occur in several distinct mineral assemblages in banded carbonatite-like marbles from the Bližná graphite mine, Český Krumlov Unit, Moldanubian Zone. The carbonatite-like marble is interlayered with dominant ordinary metacarbonates as a single continuous stratabound layer, up to 3-4 m thick. It is enriched in elements typical for carbonatites (REE, Y, Th, Sr, Nb, Zr, and Mo) and contains accessory betafite-pyrochlore and uranothorite along with molybdenite, sulfides (e.g., pyrite, pyrrhotite) and oxides (e.g., magnetite, ilmenite). Detailed study of thin sections in optical microscope and BSE images as well as results of EMPA revealed three distinct mineral assemblages - richterite + forsterite (RF) assemblage (Rht + Fo + Cal ˃ Dol ˃ Phl + Di), Na rich actinolite + diopside (AD) assemblage (Di + Act + Rht + Cal ˃ Phl) and magnesio-hastingsite + diopside (HD) assemblage (Mhst + Di + Cal ˃ Ab + Phl). The distinct amphibole species found within the individual assemblages exhibit complex textural relations and crystallized in several prograde and retrograde stages. The following amphibole species were recognized in the individual assemblages: RF - (richterite > ferri-winchite > tremolite, edenite), AD - (actinolite > ferri-winchite; richterite > ferri-katophorite; magnesio-riebeckite), HD - (magnesio-hastingsite; ferri-winchite, actinolite). They differ especially in Mg/(Mg + Fetot) ratio and concentrations of F. Diopside contains up to 17 mol. % of the aegirine component and albite is Fe, Ba-enriched (≥ 0.69 wt. % BaO and ≥ 0.50 wt. % Fe2O3tot). The composition of amphiboles and pyroxenes indicates the alkaline environment of their formation; unusually high Fe2O3 contents in albite plagioclase have known counterparts in alkaline pegmatites and some carbonatite dykes. The following options of potential origin of the carbonatite-like marble from Bližná are discussed: (i) metacarbonates potentially with Na- and Na,Ca-carbonates and sulfate admixture; (ii) admixture of alkaline volcanodetritic component during carbonate sedimentation; (iii) metamorphosed carbonatites enclosed in ordinary sedimentary metacarbonate; (iv) Na-rich metasomatites characterized by mineral assemblages with Na,Fe,F-enriched amphiboles, diopside with high aegirine component and albite. With regard to the observed mineral assemblages, textures and composition of minerals, we can exclude (i) marine evaporates, whereas the other options (ii), (iii) and (iv) are, in general, possible. The amphiboles observed in the Bližná carbonatite-like marble are unique within the Bohemian Massif and distinctly different from amphiboles found in metacarbonates with evaporite component.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10504 - Mineralogy

Projekt

<a href="/cs/project/GA19-05198S" target="_blank" >GA19-05198S: Greisenizace a albitizace - geologické procesy s potenciálem koncentrovat některé kritické suroviny pro moderní technologie</a><br>

Návaznosti

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Rok uplatnění

2021

Kód důvěrnosti údajů

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

Název periodika

Journal of Geosciences

ISSN

1802-6222

e-ISSN

1803-1943

Svazek periodika

66

Číslo periodika v rámci svazku

4

Stát vydavatele periodika

CZ - Česká republika

Počet stran výsledku

20

Strana od-do

243-262

Kód UT WoS článku

000738385300008

EID výsledku v databázi Scopus

—