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Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

Shulamitite and its Fe-analog in metacarbonate xenoliths from alkali basalts, E. Eifel, Germany

Sharygin V.V.*, Wirth R.**

* V.S.Sobolev Institute of Geology and Mineralogy SD RAS, Novosibirsk, Russia; ** Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany

sharygin@igm.nsc.ru

The phase Ca₃TiFe₂O₈ (Grenier phase) was firstly synthesized in 70^th years of last century (Grenier et al., 1976). It was a first “layered perovskite” (CaTiO₃∙Ca₂Fe₂O₅), an intermediate member of the pseudobinary series perovskite CaTiO₃ - brownmillerite Ca₂(Fe,Al)₂O₅. Shulamitite Ca₃TiFeAlO₈, a natural Al-rich analog of Ca₃TiFe₂O₈, was recently found in larnite rocks from the Hatrurim Basin, Israel (Sharygin et al., 2008) and approved by IMA as a new mineral (Sharygin et al., 2011). At present shulamitite and its Fe-rich analog were also observed in other natural and technogenic metacarbonate rocks (Galuskin et al., 2008; Niedermayr et al., 2011; Sharygin, 2011). This report is devoted to chemical composition of these phases and structural information for Fe-rich analog of shulamitite from metacarbonate xenoliths in alkali basalts of the Bellerberg volcano, E. Eifel, Germany. Mineralogical description for one of xenolith containing shulamitite and its Fe-analog is given by Sharygin (2012).

In the Eifel xenoliths these phases coexist with perovskite or brownmillerite-srebrodolskite, sometimes occur together (Fig. 1). It should be noted that Fe-analog is most common of the xenolith’s zones nearby the contact with basalt. In the case of their coexistence shulamitite is earlier phase than Fe-analog. Representative compositions of shulamitite and Fe-analog are given in Table, whereas their compositional variations are shown in Fig. 1. Namely their broad variation in Al and Fe³⁺ in the Eifel xenoliths gave severe grounds for the existence of the isomorphic series Ca₃TiFeAlO₈-Ca₃TiFeFeO₈ in natural samples. In addition, these phases near the contact with basalt are richer in SrO (up to 2 wt.%) what is common of all Ca-minerals in the xenoliths studied.

Fig. 1. Shulamitite and its Fe-analog in the Eifel metacarbonate xenolith (sample Å-2011, scanning microscopy) and their compositional variations. Symbols: Shu - shulamitite, Fe-Shu - Fe-analog of shulamitite, Prv - perovskite, Brm - brownmillerite, Yel - ye’elimite, Lar - larnite, Per - periclase. The association T-17 is located nearer the contact with basalt than Ò-30. Selected area is the position of foil for TEM.

Table. Chemical composition (wt.%) of shulamitite and its Fe-analog in metacarbonate xenoliths, E. Eifel.

FeO and Fe₂O₃ are calculated by stoichiometry for formula based on 6 cations and 8 oxygens, n - number of analyses.

Three FIB-prepared foils with Fe-analog of shulamitite from two Eifel xenoliths (E-2011, M7-184) were used for transmission electron microscopy (TEM) studies (Wirth, 2009). These investigations have shown that in all samples this phase is homogeneous in composition and does not contain any domains and solid phase decay structures (Fig. 2). In addition some interplanar distances and a cell parameter (à ≈ 5.41 Å) are calculated, which are very close to those in holotype shulamitite (a = 5.42 Å, Sharygin et al., 2011). The studies in bright and dark field regime have indicated that polysynthetic microtwinning is common of some “Fe-shulamitite” grains, especially in association with perovskite and shulamitite (sample Å-2011, Fig. 3). Such twinning also occurs in the neighboring perovskite. Investigations in this regime are also revealed structural inhomogeneity in Fe-analog of shulamitite, which seems to be related to order-disorder phenomena in the structure. There is no saying what type of this order-disorder. It is quite possible this indicates partial ordering in the tetrahedral or octahedral layers. TEM data obtained suggest the structural similarity of shulamitite and Fe-analog and also support the reality of the isomorphic series Ca₃TiFeAlO₈-Ca₃TiFeFeO₈.

Fig. 2. HRTEM images for Fe-analog of shulamitite (sample Å-2011, E. Eifel).

Fig. 3. Order-disorder and twinning in Fe-analog of shulamitite (TEM, dark and bright field images).

The authors would like to thank B. Ternes and W. Schüller (Germany) for donating of metacarbonate xenoliths from E. Eifel. Many thanks to A. Schreiber (Potsdam, Germany) for preparing of the FIB-milled foils for TEM.

References

Galuskin E.V., Gazeev V.M., Armbruster T., Zadov A.E., Galuskina I.O., Pertsev N.N., Dzierzanovski P., Kadiyski M., Gurbanov A.G., Wrzalik R., Winiarski A. Lakargiite CaZrO₃: A new mineral of the perovskite group from the Northern Caucasus, Kabardino-Balkaria, Russia // American Mineralogist. 2008. V. 93. P. 1903-1910.

Grenier J.-C., Darriet J., Pouchard M., Hagenmuller P. Mise en evidnece d’une nouvelle fammille de phases de type perovskite lacunaire ordonnee de formule A₃M₃O₈ (AMO_2,67) // Materials Research Bulletin. 1976. V. 11. P. 1219-1226.

Niedermayr G., Auer C., Bernhard F., Brandstätter F., Gröbner J., Hammer V.M.F., Knobloch G., Koch G., Kolitsch U., Konzett J., Leikauf B., Löffler E., Postl W., Prasnik H., Prayer A., Pristacz H., Sabor M., Seemann R., Stehlik H., Thinschmidt A., Walter F. Neue Mineralfunde aus Österreich LX // Carinthia II. 2011. V. 201./121. P. 135-186.

Sharygin V.V. Lakargiite and minerals of the perovskite-brownmillerite series in metacarbonate rocks from Donetsk burned dumps // Proceedings of Donetsk National Technical University, Mining and Geological Series. V. 15 (192). P. 113-123 (in Russian).

Sharygin V.V. Mineralogy of metacarbonate xenolith from alkali basalt, E. Eifel, Germany // Abstracts of International conference “Ore potential of alkaline, kimberlite and carbonatite magmatism”, School “Alkaline magmatism of the Earth”, Sudak, Ukraine, 2012.

Sharygin V.V., Lazic B., Armbruster T., Murashko M.N., Wirth R., Galuskina I.O., Galuskin E.V., Vapnik Y. Shulamitite, IMA 2011-016. CNMNC Newsletter No. 10. October 2011. P. 2552 // Mineralogical Magazine. 2011. V. 75, No. 5. P. 2549-2561.

Sharygin V.V., Sokol E.V., Vapnik Ye. Minerals of the pseudobinary perovskite-brownmillerite series from combustion metamorphic larnite rocks of the Hatrurim Formation (Israel). Russian Geology and Geophysics. 2008. V.49 (10). P. 709-726.

Wirth R. Focused Ion Beam (FIB) combined with SEM and TEM: Advanced analytical tools for studies of chemical composition, microstructure and crystal structure in geomaterials on a nanometer scale // Chemical Geology. 2009. V. 261. P. 217-229.