Micro- to nanoscale constraints on metasomatic alterations of xenotime, inclusions of Th-, U- and Pb-phases and their geochronological implications (Ås pegmatite, Evje and Hornnes, S Norway)

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F67985831%3A_____%2F23%3A00571838" target="_blank" >RIV/67985831:_____/23:00571838 - isvavai.cz</a>

Result on the web

<a href="https://www.sciencedirect.com/science/article/pii/S0009254123002383?via%3Dihub" target="_blank" >https://www.sciencedirect.com/science/article/pii/S0009254123002383?via%3Dihub</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1016/j.chemgeo.2023.121538" target="_blank" >10.1016/j.chemgeo.2023.121538</a>

Result language

angličtina

Original language name

Micro- to nanoscale constraints on metasomatic alterations of xenotime, inclusions of Th-, U- and Pb-phases and their geochronological implications (Ås pegmatite, Evje and Hornnes, S Norway)

Original language description

Five crystals of pegmatitic xenotime from Ås II feldspar quarry (Evje, S Norway) were studied with comprehensive analytical methods from microscale to nanoscale with respect to fluid-mediated alterations and their geochronological implications. Xenotime crystals are strongly altered during dissolution-reprecipitation processes that resulted in the formation of (Th, U)-depleted xenotime subdomains with numerous microinclusions of (Th, U)-silicate, uraninite and minor galena. Remains of a primary xenotime (Xtm1) yielded LA-ICPMS U-Pb data characterized by a reverse discordance (from −10.5 to −2.6%) with a 208Pb/232Th mean age 988.4 ± 5.9 Ma (95% conf., MSWD = 0.75, n = 71), which is within uncertainty with a 207Pb/235U mean age 979.1 ± 5.0 Ma (95% conf., MSWD = 1.4, n = 22) yielded by data filtered to below ±5% discordance (i.e., from −5.0 to −2.6%). The altered xenotime domains (Xtm2) provided highly scattered dates, including 208Pb/232Th dates from 200 ± 14 to 2135 ± 120 Ma (n = 135). Discordant U-Pb data yielded upper intercept age 909 ± 16 Ma (MSWD = 7.9). EPMA Th-U-total Pb measurements and compositional characteristics of uraninite inclusions indicate three age populations of ca. 852–983, 594–687 and 37–101 Ma. TEM investigations revealed initial alterations within domains Xtm1, representing a primary xenotime, which progressed along parallel submicron- to nanoscale fractures. These fractures represent partially open grain boundaries, which are empty or are filled with secondary inclusions of (Th, U)-silicates, uraninite or coffinite. The submicron-sized inclusions are accompanied by subdomains of (Th, U)-depleted xenotime. Altered xenotime (Xtm2) is well crystalline in TEM imaging and electron diffraction patterns in contrast to primary unaltered xenotime domains (Xtm1) that demonstrate, in Raman spectra, moderate degree of radiation damage caused by U and Th decay. Secondary inclusions of Th and U phases are nanocrystalline or amorphous, which increases their potential for Pb-loss or accumulation of Pb in excess. Some of them contain nanoinclusions of Pb3O4 or metallic Pb, whereas <100 nm-sized inclusions of (Pb, Sb)-oxide formed in the altered xenotime. To summarize, this study provides important insights for our understanding of coupled dissolution-reprecipitation processes that affect xenotime and mobilization of released U, Th and Pb. Removal of highly mobile U in a fluid, and the presence of nanoinclusions of Pb3O4, (Pb, Sb)-oxide and metallic Pb have particular importance for xenotime dating and explain disturbance towards older ages. Nevertheless, both removal of U, Th and Pb from altered and recrystallized xenotime as well as presence of submicron- to nanoinclusions can result in age disturbance resulting in spread of dates along a concordia curve.

Czech name

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Czech description

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Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

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OECD FORD branch

10504 - Mineralogy

Project

—

Continuities

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2023

Confidentiality

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

Name of the periodical

Chemical Geology

ISSN

0009-2541

e-ISSN

1872-6836

Volume of the periodical

632

Issue of the periodical within the volume

August

Country of publishing house

NL - THE KINGDOM OF THE NETHERLANDS

Number of pages

23

Pages from-to

121538

UT code for WoS article

001008766800001

EID of the result in the Scopus database

2-s2.0-85159183387