Stable (C, O) and radiogenic (Sr, Nd) isotopic evidence for REE-carbonatite formation processes in Petyayan-Vara (Vuoriyarvi massif, NW Russia).
In: Lithos, Jg. 398 (2021-10-01), S. N.PAG
Online
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Zugriff:
A study of radiogenic (Sr, Nd) and stable (C, O) isotopic data for rare earth carbonatites from the Petyayan-Vara field of the Devonian Vuoriyarvi alkaline-ultrabasic massif is presented. The cumulative evidence indicates that the primary igneous rocks of the Petyayan-Vara area are burbankite-bearing magnesiocarbonatites having isotopic signatures of the depleted mantle (εNd 365Ma = 5.0, 87Sr/86Sr (i) = 0.7031, δ13C ca. –4‰, and δ18O ca. 11‰). Interaction of the primary carbonatite melt with the host silicate rocks produced high-Ti carbonatites with a mantle δ13C (ca. –4‰) and isotopically heavy δ18O (ca. 20‰). These rocks trapped K, Na, Mg, CO 2 , and rare earth elements (REEs) (mainly heavy REEs) from the melt and Si, Al, Fe, Ti, and P from the host rocks. Early post-magmatic exposure of burbankite-bearing carbonatites to a mixture of fluids of crustal and orthomagmatic carbonatite origin caused redistribution of REEs, Ba, and Sr and formation of REE-rich carbonatites with abundant ancylite mineralization. This effect did not disturb the Sm Nd system but induced radiogenic Sr accumulation and a change in C and O isotopic composition towards heavier values. Later, but most likely before denudation, the Petyayan-Vara rocks underwent another metasomatic event involving crustal fluids infiltrating through fracture systems. This event triggered formation of bastnäsite-rich carbonatites with fewer REEs at the expense of ancylite-rich carbonatites, and changed all the isotopic systems in the affected rocks. This model successfully accounts for the evolution of all the carbonatite varieties discovered to date in the Petyayan-Vara field. [Display omitted] • The evolutionary model for Petyayan-Vara REE-carbonatites is presented. • Burbankite-bearing magnesiocarbonatites of Petyayan-Vara are primary igneous rocks. • Early postmagmatic processes have produced high-REEs ancylite-rich carbonatites. • Crustal fluid transformed ancylite-rich rocks into bastnäsite-rich carbonatites. [ABSTRACT FROM AUTHOR]
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Stable (C, O) and radiogenic (Sr, Nd) isotopic evidence for REE-carbonatite formation processes in Petyayan-Vara (Vuoriyarvi massif, NW Russia).
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Autor/in / Beteiligte Person: | Fomina, Ekaterina N. ; Kozlov, Evgeniy N. |
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Zeitschrift: | Lithos, Jg. 398 (2021-10-01), S. N.PAG |
Veröffentlichung: | 2021 |
Medientyp: | academicJournal |
ISSN: | 0024-4937 (print) |
DOI: | 10.1016/j.lithos.2021.106282 |
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