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The stability of primary alluaudites in granitic pegmatites: an experimental investigation of the Na2(Mn2–2xFe1+2x)(PO4)3 system.
Авторы: Hatert F., Fransolet A., Maresch W.
2006 г.
Contrib.Miner.Petrol.
In order to assess the geothermometric potential of the Na2(Mn2–2xFe1+2x)(PO4)3 system (x = 0–1), which represents the compositions of natural weakly oxidized alluaudites, we performed hydrothermal experiments between 400 and 800C, at 1 kbar, under an oxygen fugacity (f(O2)) controlled by the Ni–NiO (NNO), Fe2O3–Fe3O4 (HM), Cu2O–CuO (CT), and Fe–Fe3O4 (MI) buffers. When f(O2) is controlled by NNO, single-phase alluaudites crystallize at 400 and 500C, whereas the association alluaudite + maric´ite appears between 500 and 700C. The limit between these two fields corresponds to the maximum temperature that can be reached by alluaudites in granitic pegmatites, because maric´ite has never been observed in these geological environments. Because alluaudites are very sensitive to variations of oxygen fugacity, the field of hagendorfite, Na2MnFe2+Fe3+ (PO4)3, has been positioned in the f(O2)–T diagram, and provides a tool that can be used to estimate the oxygen fugacity conditions that prevailed in granitic pegmatites during the crystallization of this phosphate.
Файл: 501.pdf
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