Issue 4(48), 2017

ISSN 2307-2091 (Print) 

ISSN 2500-2414 (Online)

DOI: http://dx.doi.org/10.21440/2307-2091-2017-4-29-35

Chemical zoning of spinels and olivines from chromitites and the enclosing ultramafites of the Rai-Iz massif Tsentralnoye deposit (The Polar Urals) [In English] PDF

P. B. Shiryaev, N. V. Vakhrusheva

The authors studied the chemical zoning of coexisting olivines and chromium spinels from chromitites and near-ore rocks of the of the Rai-Iz massif Tsentralnoye deposit. There are two types of zoning. The first type appears both in accessory and in ore-forming spinels and olivines and occurs at the contact of minerals due to the redistribution of Fe and Mg cations between them. On approaching the grain contact the Fe/(Fe + Mg) in olivine decreases while in spinel it increases. In both minerals the Cr2O3 content increases to the grain rims. This zoning has been formed under the conditions of temperature decreasing and oxygen fugacity rising. The second type of spinel zoning can be observed in plastically deformed enstatite-olivine rocks, the products of harzburgite metamorphism. It is characterized by the Fe content decreasement and the Cr2O3 increasement from the inner parts of spinel and olivine grains to their contact. The formation of this zoning occurred at a constant temperature and oxygen fugacity. The first type of zoning is well studied and widely discussed in literature, but zoning of the second type is relatively rare. The similar distribution of elements is observed in the grains of accessory spinels of the Miyamori and Hiroman massifs (Japan), where it is considered as the result of kinetic redistribution of chemical components in the mineral structure that occurs under the influence of Nabarro-Herrnig diffusion creep in conditions of directed stress. The presence of plastic deformation signs (dynamic recrystallization zones and polysynthetic twinning in olivine grains) in the studied enstatite-olivine rock sample also permits the authors to interpret the zoning of accessory spinels as the result of kinetic diffusion redistribution of components in the mineral grain under stress conditions.

Keywords: olivine; chrome-spinel; chemical zoning; chromitites; ultramafic rocks; Rai-Iz massif; Polar Urals.

 

REFERENCES

1. 1990, Stroenie, ehvolyutsiya i minerageniya giperbazitovogo massiva Raj-Iz [The structure, evolution and minerageny of the Rai-Iz hyperbasite massif]. Ed. by V. N. Puchkov, D. S. Shteinberg. Sverdlovsk, 228 p.

2. Bliss N. W., MacLean W. H. 1975, The paragenesis of zoned chromite from central Manitoba. Geochimica et Cosmochimica Acta, vol. 39, pp. 973–990.

3. Colás V., González-Jiménez J. M., Griffin W. L., Fanlo I., Gervilla F., O’Reilly S. Y., Pearson N. J., Kerestedjian Th., Proenza J. A. 2014, Fingerprints of metamorphism in chromite: New insights from minor and trace elements. Chemical Geology, vol. 389, pp. 137–152.

4. Evans B. W., Frost B. R. 1975, Chrome-spinel in progressive metamorphism – a preliminary analysis. Geochimica et Cosmochimica Acta, vol. 39, pp. 959–972.

5. Ozawa K. 1989, Stress-induced Al-Cr zoning of spinel in deformed peridotites. Nature, vol. 338, pp. 141–144.

6. Satsukawa T., Piazolo S., González-Jiménez J. M., Colás V., Griffin W. L., O’Reilly S. Y., Gervilla F., Fanlo I., Kerestedjian Th. N. 2015, Fluid-present deformation aids chemical modification of chromite: Insights from chromites from Golyamo Kamenyane, SE Bulgaria. Lithos, vol. 228-229, pp. 78–89.

7. Suzuki A. M., Yasuda A., Ozawa K. 2008, Cr and Al diffusion in chromite spinel: experimental determination and its implication for diffusion creep. Physics Chemistry Minerals, vol. 35, pp. 433-445.

8. Lehmann J. 1983, Diffusion between olivine and spinel application to geothermometry. Earth Planetary Science Letters, vol. 64, pp. 123–138.

9. Ozawa K. 1984, Olivine-spinel geospeedometry: Analysis of diffusion-controlled Mg–Fe2+ exchange. Geochimica et Cosmochimica Acta, vol. 48, pp. 2591–2611.

10. Ballhaus C., Berry R. F., Green D. H. 1991, Experimental calibration of the olivine-orthopyroxene-spinel oxygen barometer – implications for oxygen fugacity in the Earth’s upper mantle. Contributions Mineralogy Petrology, vol. 107, pp. 27–40.

11. Shiryaev P. B., Vakhrusheva N. V. 2016, Olivin-khromshpinelevoe ravnovesie v khromititakh i ul’tramafitakh massiva Raj-Iz [Olivine-chrome spinel equilibrium in chromitites and ultramafites of the Rai-Iz massif]. Litosfera [Litosfera], no. 2, pp. 107–110.

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