Partial resetting of U–Pb ages during experimental fluid-induced re-equilibration of xenotime

0509442 - GLÚ 2020 RIV NL eng J - Journal Article
Budzyń, B. - Sláma, Jiří
Partial resetting of U–Pb ages during experimental fluid-induced re-equilibration of xenotime.
Lithos. 346-347, December (2019), s. 346-347, č. článku 105163. ISSN 0024-4937. E-ISSN 1872-6143
Institutional support: RVO:67985831
Keywords : Dissolution-reprecipitation * mineral-fluid reactions * geochronology * secondary textures * xenotime
OECD category: Geology
Impact factor: 3.390, year: 2019
Method of publishing: Limited access
https://www.sciencedirect.com/science/article/pii/S0024493719303202?via%3Dihub

Experimentally metasomatized xenotime was investigated in terms of preservation of U–Pb ages during fluid-induced alterations at 250, 450, 550 and 650 °C. Starting materials for experiments included xenotime (38.4 ± 0.6 Ma), albite, K-feldspar, biotite, muscovite, garnet, SiO₂, CaF₂, Na₂Si₂O₅ and H₂O that roughly replicated metapelitic to granitic composition with high Na, Ca, Si and F activities in the fluid. Despite partial replacement of xenotime by secondary phases including (Y,REE)-rich fluorapatite to Y-rich fluorcalciobritholite in all runs, and an unnamed (Y,HREE)-rich silicate in 250 °C experiment, only two experiments at 550 °C, 800 MPa and 650 °C, 600 MPa resulted in development of faint to moderate patchy zoning in the xenotime. Experimental results indicate higher chemical-stability of xenotime at lower P-T conditions compared to those corresponding to amphibolite facies conditions. The xenotime domains metasomatized via coupled dissolution-reprecipitation reactions are characterized by depletion of U and Pb and younger ²⁰⁶Pb/²³⁸U dates of ca. 15–34 Ma, demonstrating preferential removal of Pb and thus the partial resetting of the age record. The U–Pb data for the first time experimentally confirm that xenotime may be affected by re-equilibration induced by fluid or melt with high Na, Ca and F activities via coupled dissolution-reprecipitation reactions that result in removal of radiogenic Pb under temperature conditions of 550–650 °C. These findings have important implications for U–Pb geochronology of igneous (particularly in pegmatites) and metamorphic processes in terms of preservation of U–Pb ages of xenotime that was affected by multiple thermal events in the presence of alkali-rich fluid and/or melt.
Permanent Link: http://hdl.handle.net/11104/0304998