Xenotime-(Y) formation from zircon dissolution–precipitation and HREE fractionation: an example from a metamorphosed phosphatic sandstone, Espinhaço fold belt (Brazil)
Xenotime-(Y) formation from zircon dissolution–precipitation and HREE fractionation: an example from a metamorphosed phosphatic sandstone, Espinhaço fold belt (Brazil)
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锆石溶解沉淀和 HREE 分馏形成的磷钇矿 (Y):以埃斯皮尼亚索褶皱带(巴西)变质磷酸盐砂岩为例
DOI:
10.1007/s00410-015-1191-y
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发表时间:
2015
影响因子:
3.5
通讯作者:
Morteani
中科院分区:
文献类型:
--
作者:
Morteani
We present an example where xenotime-(Y) together with metamorphic zircon replaces detrital zircon in a phosphatic sandstone from the Mesoproterozoic Espinhaço fold belt, Brazil, in a dissolution–precipitation reaction:$${\text{zircon}}_{1} \left( {\text{relict}} \right) + {\text{P-}}{\text{bearing fluid}} = {\text{zircon}}_{2} \left( {\text{metamorphic}} \right) + {\text{xenotime}}.$$ zircon 1 relict + P- bearing fluid = zircon 2 metamorphic + xenotime . During the Brasiliano orogeny at 634 ± 19 Ma, the rocks experienced amphibolite facies metamorphism at ≥0.6 GPa/~550 ± 37 °C (Southern Espinhaço) and ≥0.6 GPa/~570 ± 35 °C (Northern Espinhaço), constrained by Zr-in-rutile and Ti-in-quartz thermometry and the presence of kyanite + muscovite + quartz. Many of the rocks show unusual rare earth element (REE) patterns with a hump at Gd–Tb–Dy and depletion in light REE. Detrital zircons (with relict ages between 1.5 and 3.3 Ga) show varying degrees of replacement as indicated by the presence of xenotime and associated porosity, from almost pristine to complete alteration. Textural evidence indicates local mobility of Zr and REE at the scale of the thin section. Xenotime-(Y) occurs together with other phosphates, mainly augelite, lazulite, and minerals of the svanbergite–crandallite–goyacite–florencite group. Xenotime-(Y) is very heterogeneous and reaches unusually high contents of up to 14 wt% Gd2O3, 13 wt% Dy2O3, and 3 wt% Tb2O3, corresponding to ≤0.36 REE atoms per formula unit due to the exchange Y = REE. The heavy REE patterns of xenotime-(Y) therefore show variable enrichment in individual elements, which explains the characteristic hump at Gd–Tb–Dy in the REE patterns of the whole rock. Although the rocks reached amphibolite facies conditions, textures indicate that formation of xenotime likely occurred during the early stages of diagenesis—metamorphism. Comparison with REE concentrations in xenotime-(Y) from the literature shows that selective REE incorporation into xenotime-(Y) is controlled by interaction with P-bearing hydrous fluids.
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影响因子:
3.1
作者:
F. Lucassen;G. Franz;D. Rhede;R. Wirth
通讯作者:
R. Wirth
DOI:
--
发表时间:
2007
期刊:
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2015
期刊:
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通讯作者:
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DOI:
--
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1988
期刊:
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