Stability of monazite and disturbance of the $Th-U-Pb$ system under experimental conditions of $250–350^{\circ}$C and 200–400 MPa
PBN-AR
Instytucja
Wydział Geologii, Geofizyki i Ochrony Środowiska (Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie)
Informacje podstawowe
Główny język publikacji
EN
Czasopismo
Annales Societatis Geologorum Poloniae
ISSN
0208-9068
EISSN
Wydawca
Polish Geological Soc.
Rok publikacji
2015
Numer zeszytu
2
Strony od-do
405--424
Numer tomu
85
Link do pełnego tekstu
Identyfikator DOI
Liczba arkuszy
1.42
Autorzy
(liczba autorów: 3)
Pozostali autorzy
+ 2
Słowa kluczowe
EN
apatite
rare earth elements
monazite
experimental petrology
geochronology
Streszczenia
Język
EN
Treść
This experimental study provides important data filling the gap in our knowledge on monazite stability under conditions of fluid-mediated low-temperature metamorphic alteration and post-magmatic hydrothermal alterations. The stability of monazite and maintenance of original Th-U-total Pb ages were tested experimentally under P-T conditions of 250-350 degrees C and 200-400 MPa over 20-40 days. The starting materials included the Burnet monazite + K-feldspar +/- albite +/- labradorite + muscovite + biotite + SiO2 + CaE, and 2M Ca(OH)(2) or Na2Si2O5 + H2O fluid. In the runs with 2M Ca(OH)(2), monazite was unaltered. REF-enriched apatite formed at 350 degrees C and 400 MPa. The presence of the Na2Si2O5 + H2O fluid promoted the strong alteration of monazite, the formation of secondary REF-enriched apatite to fluorcalciobritholite, and the formation of REF-rich steacyite. Monazite alteration included the newly developed porosity. patchy zoning, and partial replacement by REE-rich steacyite. The unaltered domains of monazite maintained the composition of the Burnet monazite and its age of (or close to) ca. 1072 Ma, while the altered domains showed random dates in the intervals of 375-771 Ma (250 degrees C. 200 MPa run), 82-253 Ma (350 degrees C, 200 MPa), and 95-635 Ma (350 degrees C, 400 MPa). The compositional alteration and disturbance of the Th-U-Pb system resulted from fluid-mediated coupled dissolution-reprecipitation. In nature, such age disturbance in monazite can be attributed to post-magmatic alteration in granitic rocks or to metasomatic alteration during metamorphism. Recognition of potentially altered domains (dark patches in high-contrast BSE-imaging. developed porosity or inclusions of secondary minerals) is crucial to the application of Th-U-Pb geochronology.
Cechy publikacji
original article
peer-reviewed
Inne
System-identifier
idp:095223
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