Coupled anion substitution in natural carbon-bearing apatites

Binder, Günter; Troll, Georg

doi:10.1007/bf00372213

Cited by 62 publications

(25 citation statements)

References 21 publications

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“…Starting with a simplified formula of the type Cal0(PO4)6(F, CI, OH)2 , the apatite analyses have been recalculated to structural formulae assuming Ca + Na + La + Ce + Nd = 10.000 cations (Le Bas and Handley, 1979). This gives P + Si in the range 5.71-6.28, so, although substitution of carbon in the form of CO3, CO3OH or CO3F groups replacing PO4 tetrahedra is possible in apatite (McConnell, 1973;Le Bas and Handley, 1979;Sommerauer and Katz-Lehnert, 1985b;Binder and Troll, 1989), it must be very small or negligible here. The CO3F substitution will not therefore have any significant effect on the total fluorine content.…”

Section: Resultsmentioning

confidence: 98%

Temperature-HF fugacity trends during crystallization of calcite carbonatite magma in the Fen complex, Norway

Andersen

Austrheim

1991

Mineral. mag.

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Calcite carbonatite (scvite), associated apatite cumulates and contact metasomatic phlogopite-rocks in the Fen complex (S. Norway) contain coexisting apatite and phlogopite. Two distinct compositional groups are recognized: fluorapatite (XF = 0.5--0.8) coexists with hydroxy-phlogopite with XF = 0.11--0.26, whereas hydroxyapatite (XF = 0.34-0.44) coexists with low-F hydroxy-phlogopite (XF --~ 0.03). Apatite-biotite geothermometry suggests that the minerals equilibrated at igneous temperatures (less than 1200 to ca. 625 ~ and were not significantly disturbed by late low-temperature re-equilibration. This, combined with HF-barometry based on apatite-fluid and phlogopite-fluid F-OH exchange equilibria, makes it possible to recognize two crystallization trends at different levels of hydrogen fluoride fugacity. The existence of such trends reflects internal buffering of the HI: fugacity by apatite and/or phlogopite. The recorded differences in HF fugacity suggest that two or more independent or semi-independent lines of magmatic descent gave rise to calcite carbonatite magma in the Fen complex. Combined apatite-phlogopite geothermometry and hydrogen fluoride barometry is a useful tool enabling us to see through post-magmatic alteration of carbonatites, and to establish primary magmatic controls even in cases where carbonate and iron-titanium oxide minerals have re-equilibrated at much lower temperatures.

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Section: Resultsmentioning

confidence: 98%

Temperature-HF fugacity trends during crystallization of calcite carbonatite magma in the Fen complex, Norway

Andersen

Austrheim

1991

Mineral. mag.

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“…In all other Ap, most researchers agree that CO3 substitutes for PO4 (e.g. McClellan, 1980;Nathan, 1984;Binder and Troll, 1989;McArthur, 1990) although neither the structural change produced by the substitution of a tetrahedral PO33-group with a triangular CO32-group, nor how the charge balance is maintained, are explained. Much chemical evidence exists to support the hypothesis of CO3/PO4 substitution such as the high inverse correlation between the P atoms and the sum of the Si, S and C atoms (Fig.…”

Section: X04 Substitutionmentioning

confidence: 99%

“…For example, many researchers think that CO3 substitutes PO4 (e.g. McClellan, 1980;Nathan 1984;Binder and Troll, 1989;McArthur, 1990) but the exact mechanism of CO3 substitution in the Ap structure is still a matter of dispute. Through comparison of the crystal chemistry of Ap samples from carbonatites, especially from early-state carbonatites, with those from alkaline igneous pegmatitic, hydrothermal, metamorphic and sedimentary rocks, we have endeavoured to gain more information on substitution mechanisms.…”

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confidence: 99%

Some aspects of the crystal-chemistry of apatites

Liu

Comodi

1993

Mineral. mag.

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Twenty-four apatite (Ap) samples mainly from carbonatite and alkaline rocks were studied by electron microprobe, IR spectroscopy and X-ray powder diffraction. The crystal structures of six were refined using single crystal X-ray diffraction data to R = 1.7-2.5%. The generally high Si content of Ap from carbonatite and alkaline rock has been related to the presence of characteristic Si-O absorptions in IR spectra. Bands, whose intensities change with Si content, were observed at 520, 650, 930 and 1160 cm -1. The IR absorption features of v3 CO3 mode of Ap from carbonatite are different from those of v3 CO3 mode of Ap from sedimentary rock. This phenomenon is probably due to the different effects of F and OH on the CO3 substitution for PO4. The structural refinements yield more information on the CO3=PO 4 substitution, which is now supported also by the geometrical evolution of the tetrahedron with increasing CO3 content: the tetrahedral size decreases and the angle distortion increases with Ccontent. It is likely that the triangular planar CO3 group is disordered on the four faces of PO4 3-tetrahedron. It was observed also that Ap from early-stage carbonatite is OH-dominant with considerable LREE, Si, CO3 and negligible Mn, Fe, Mg, K, S and C1 contents. They have high Sr/Mn, Si/S and C/S ratios.

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“…These two elements occur in many metamorphic rockforming minerals and consequently can be determined in order to estimate their ratios in metamorphic fluids (Munoz and Swenson, 1981;Zhu and Sverjensky, 1991;Harley and Buick, 1992;Markl and Bucher, 1998). As a result, the chemistry of scapolite, and particularly its Cl and CO2 contents, in relation to the Cl and F content of other coexisting common metamorphic rockforming minerals, such as amphibole, mica, apatite and titanite, can be used as tracers for the chemical composition of the metamorphic fluid (Ellis, 1978;Munoz and Swenson, 1981;Binder and Troll, 1989;Mora and Valley, 1989;Kullerud, 1996;Rebbert and Rice, 1997;Markl and Bucher, 1998;Kullerud and Erambert, 1999;Yardley et al, 2000;Svensen et al, 2001). …”

Section: Discussionmentioning

confidence: 99%