A detailed and comprehensive TEM, EPMA and Raman characterization of high-metamorphic grade monazites and their U-Th-Pb systematics (the Góry Sowie Block, SW Poland)

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F67985831%3A_____%2F22%3A00559644" target="_blank" >RIV/67985831:_____/22:00559644 - isvavai.cz</a>

Výsledek na webu

<a href="https://www.sciencedirect.com/science/article/pii/S0009254122003096" target="_blank" >https://www.sciencedirect.com/science/article/pii/S0009254122003096</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1016/j.chemgeo.2022.121015" target="_blank" >10.1016/j.chemgeo.2022.121015</a>

Jazyk výsledku

angličtina

Název v původním jazyce

A detailed and comprehensive TEM, EPMA and Raman characterization of high-metamorphic grade monazites and their U-Th-Pb systematics (the Góry Sowie Block, SW Poland)

Popis výsledku v původním jazyce

Eleven monazite grains, two from a migmatitic gneiss and nine from two felsic granulites from the Gory Sowie Block (SW Poland) were studied with transmission electron microscopy (TEM), electron probe microanalysis (EPMA), Raman microspectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) U-Th-Pb analysis in order to assess processes affecting U-Th-Pb age record. Two monazite grains from the migmatitic gneiss are patchy zoned in BSE imaging and overgrown by allanite, whereas Raman results indicate moderate radiation damage. Monazite in the corresponding TEM foils shows twins and nanoinclusions of fluorapatite, thorianite, goethite, titanite, chlorite and CaSO4. Furthermore, monazite is partially replaced by secondary monazite, forming ca. 100 nm-thick layers, and calcite along grain boundaries. The submicron alterations had little or no effect on the Pb/U and Pb/Th dates, when compared to earlier age constraints on the metamorphism in the studied region. In contrast, monazite from both granulites is homogeneous in eight investigated TEM foils, contains no solid or fluid nanoinclusions or any signs of fluid-induced alterations, with only one exception of a ca. 140 nm-thick crack filled with monazite. The 206Pb/238U and marginally older 208Pb/232Th mean dates pulled for all data show good coherence. However, the 207Pb/235U isotopic record is disturbed due the presence of common Pb within the entire monazite grain in one granulite and in the cores of two monazite grains in the second granulite, where the U-Pb data of the rims are not compromised and concordant. Due to lack of TEM evidence for fluid-mediated alterations, the age discordance has to be related to addition of common Pb in the monazite lattice or in the micro-cracks. To summarize, the 208Pb/232Th data reveal the most accurate ages, which are consistent with previous geochronological studies in the region. Therefore, the Pb/Th chronometer, which is less compromised by age disturbance compared to Pb/U ages, is recommended for monazite geochronology. Application of the submicron scale investigations using TEM is recommended to evaluate potential presence of the submicron inclusions of Pb-bearing phases or compositional alterations of monazite that can remain unnoticed by using standard microanalytical instruments.

Název v anglickém jazyce

A detailed and comprehensive TEM, EPMA and Raman characterization of high-metamorphic grade monazites and their U-Th-Pb systematics (the Góry Sowie Block, SW Poland)

Popis výsledku anglicky

Eleven monazite grains, two from a migmatitic gneiss and nine from two felsic granulites from the Gory Sowie Block (SW Poland) were studied with transmission electron microscopy (TEM), electron probe microanalysis (EPMA), Raman microspectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) U-Th-Pb analysis in order to assess processes affecting U-Th-Pb age record. Two monazite grains from the migmatitic gneiss are patchy zoned in BSE imaging and overgrown by allanite, whereas Raman results indicate moderate radiation damage. Monazite in the corresponding TEM foils shows twins and nanoinclusions of fluorapatite, thorianite, goethite, titanite, chlorite and CaSO4. Furthermore, monazite is partially replaced by secondary monazite, forming ca. 100 nm-thick layers, and calcite along grain boundaries. The submicron alterations had little or no effect on the Pb/U and Pb/Th dates, when compared to earlier age constraints on the metamorphism in the studied region. In contrast, monazite from both granulites is homogeneous in eight investigated TEM foils, contains no solid or fluid nanoinclusions or any signs of fluid-induced alterations, with only one exception of a ca. 140 nm-thick crack filled with monazite. The 206Pb/238U and marginally older 208Pb/232Th mean dates pulled for all data show good coherence. However, the 207Pb/235U isotopic record is disturbed due the presence of common Pb within the entire monazite grain in one granulite and in the cores of two monazite grains in the second granulite, where the U-Pb data of the rims are not compromised and concordant. Due to lack of TEM evidence for fluid-mediated alterations, the age discordance has to be related to addition of common Pb in the monazite lattice or in the micro-cracks. To summarize, the 208Pb/232Th data reveal the most accurate ages, which are consistent with previous geochronological studies in the region. Therefore, the Pb/Th chronometer, which is less compromised by age disturbance compared to Pb/U ages, is recommended for monazite geochronology. Application of the submicron scale investigations using TEM is recommended to evaluate potential presence of the submicron inclusions of Pb-bearing phases or compositional alterations of monazite that can remain unnoticed by using standard microanalytical instruments.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10505 - Geology

Projekt

—

Návaznosti

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Rok uplatnění

2022

Kód důvěrnosti údajů

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

Název periodika

Chemical Geology

ISSN

0009-2541

e-ISSN

1872-6836

Svazek periodika

607

Číslo periodika v rámci svazku

September

Stát vydavatele periodika

NL - Nizozemsko

Počet stran výsledku

17

Strana od-do

121015

Kód UT WoS článku

000828910600002

EID výsledku v databázi Scopus

2-s2.0-85134237414