Accessory chromian spinels of lherzolites and dunites from a mantle section of the Nurali ophiolite massif are described in the paper. Lherzolites typically host anhedral chromian spinel grains associated with olivine, pyroxenes and plagioclase. The compositions of silicates and chromian spinels are typical of those from ophiolite mantle sections. Olivine and orthopyroxene are characterized by high Mg content (forsterite and enstatite); clinopyroxene is diopside. The compositions of chromian spinel on the Al-Cr-Fe+3 plot occur close to the Al-Cr side. The #Cr and #Mg values of chromian spinels increase from lherzolites to dunites. Both vermicular spinels trapping olivine and orthopyroxene fragments (type I) and symplectite-like intergrowths of chromian spinel and plagioclase (type II) are most genetically interesting. Type I formed during synkinematic growth in deformed silicate matrix. Type II possibly formed as a result of decompression breakdown of a high-P mineral phase enriched in Cr, Al and Ca (a knorringite-type garnet?). In dunites, numerous tiny chromian spinel rods (type IV) in plastic deformed olivine are observed along with typical euhedral chromian spinel (type III) with inclusions of olivine and pargasite. Latter ones locally occur closely to fne pargasite grains. The formation of chromian spinel rods is explained as a result deformation-induced segregation of trace elements on the structural defects of the olivine lattice.

Figures 7. Tables 4. References 48.

Key words: chromian spinel, ultramafc rock, ophiolite, South Urals, Nurali massif.

D.E. Saveliev, Ufa Federal Science Center, Russian Academy of Sciences, ul. K. Marx, 16/2, Ufa, 450077 Russia; savl71@mail.ru

1. Arai S. (1978) Chromian spinel lamellae in olivine from the Iwanai-Dake peridotite mass, Hokkaido, Japan. Earth and Planetary Science Letters, 39, 267–273.
2. Arai S. (1980) Dunite-harzburgite-chromitite complexes as refractory residue in the Sangun-Yamaguchi zone, western Japan. Journal of Petrology, 21, 141–165.
3. Arai S. (1994) Characterization of spinel peridotites by olivine-spinel compositional relationships: Review and interpretation. Chemical Geology, 113, 191–204.
4. Ashchepkov I.V. (2018) [Structure and evolution of litospheric mantle of the Siberian platform and its frame on the basis of thermobarometric and geochemical study of deep inclusions in mantle magmas]. PhD dissertation. Novosibirsk, 574 p. (in Russian)
5. Auge T. (1987) Chromite deposits in the northern Oman ophiolite: mineralogical constraints. Mineralium Deposita, 22, 1–10.
   Barnes S.J., Roeder P.L. (2001) The range of spinel compositions in terrestrial mafc and ultramafc rocks. Journal of Petrology, 42, 2279–2302.
6. Ащепков И.В. (2018) Строение и эволюция литос-ферной мантии Сибирской платформы и ее обрамления по данным термобарометрии и геохимии глубинных включений мантийных магм. Диссертация …. доктора геол.-мин. наук. Новосибирск. 574 с.
7. Beccaluva L., Macciotta G., Piccardo G.B., Zeda O. (1984) Petrology of lherzolitic rocks from the Northern Apennine ophiolites. Lithos, 17, 299–316.
8. Bell P.M., Mao H.K., Roedder E., Weiblen P.W. (1975) The problem of the origin of symplectites in olivine-bearing lunar rocks. Proceedings of the Sixth Lunar Science Conference, 1, 231–248.
9. Borisova A.Y., Ceuleneer, G., Kamenetsky V.S., Arai S., Béjina F., Abily B., Bindeman I.N., Polvé, M., De Parseval P., Aigouy T., Pokrovski G.S. (2012) A new view on the petrogenesis of the Oman ophiolite chromitites from microanalyses of chromite-hosted inclusions. Journal of Petrology, 53, 2411–2440.
10. Dick H.J.B., Bullen T. (1984) Chromian spinel as a petrogenetic indicator in abyssal and Alpine-type peridotites and spatially associated lavas. Contributon to Mineralogy and Petrology, 86, 54–76.
11. Franz L., Wirth R. (2000) Spinel inclusions in olivine of peridotite xenoliths from TUBAF seamount (Bismarck Archipelago / Papua New Guinea): evidence for the thermal and tectonic evolution of the oceanic lithosphere. Contributions to Mineralogy and Petrology, 140, 283–295.
12. Gaidies F., Milke R., Heinrich W., Abart R. (2017) Metamorphic mineral reactions: Porphyroblast, corona and symplectite growth. EMU Notes in Mineralogy, 16(14), 469–540. DOI: 10.1180/EMU-notes.16.14
    Gorelik S.S. (1978) [Recrystallization of metals and alloys]. Moscow, Metallurgiya, 568 p. (in Russian)
13. Green H.W., Gueguen Y. (1983) Deformation of peridotite in the mantle and extraction by kimberlite; a case history documented by fuid and solid precipitates in olivine. In: Etheridge M.A., Cox S.F. (eds) Deformation processes in tectonics. Tectonophysics, 92, 71–92.
14. Grew E.S., Locock A.J., Mills S., Galuskina I.O., Galuskin E.V., Hålenius U. (2013) Nomenclature of the garnet supergroup. American Mineralogist, 98, 785–811.
15. Johan Z., Martin R.F., Ettler V. (2017) Fluids are bound to be involved in the formation of ophiolitic chromite deposits. European Journal of Mineralogy, 29, 543–555.
16. Johnson C. (2012) Podiform chromite at Voskhod, Kazakhstan. Ph.D. thesis, Cardif University, 468 p.
17. Karato S.-I. (2008) Deformation of Earth Materials. An introduction to the rheology of Solid Earth. Cambridge University Press. 463 p.
18. Leblanc M. (1980) Chromite Growth, Dissolution and Deformation from a Morphological View Point: SEM Investigations. Mineralium Deposita (Berl.), 15, 201–210.
19. Makeev A.B., Bryanchaninova N.I. (1999) [Topomineralogy of Polar Urals ultramafc rocks] St. Peterburg, Nauka, 252 p. (in Russian)
20. McElduf B., Stumpf E.F. (1991) The chromite deposits of the Troodos complex, Cyprus – evidence for the role of a fuid phase accompanying chromite formation. Mineralium Deposita, 26, 307–318.
21. Mercier J.C., Nicolas A. (1975) Textures and fabrics of upper mantle peridotites as illustrated by basalt xenoliths. Journal of Petrology, 16, 454-487.
22. Miura M., Arai S., Ahmed A.H., Mizukami T., Okuno M., Yamamoto S. (2012) Podiform chromitite classifcation revisited: a comparison of discordant and concordant chromitite pods from WadiHilti, northern Oman opiolite. Journal of Asian Earth Science, 59, 52-61.
23. Morishita T., Andal E.S., Arai S., Ishida Y. (2006) Podiform chromitites in the lherzolite-dominant mantle section of the Isabela ophiolite, the Philippines. Island Arc, 15, 84-101.
24. Moutte J. (1982) Chromite deposita of the Tiebaghi ultramafc massif, New Caledonia. Economic Geology, 77, 576-591.
25. Nicolas A. (1986) Structure and petrology of peridotites: clues to their geodynamic environment. Reviews of Geophysics, 24, 875-895.
    Nicolas A., Dupuy C. (1984) Origin of ophiolitic and oceanic lherzolites. Tectonophysics, 110, 177-187.
26. Nielson-Pike J.E., Schwarzman E.C. (1977) Classifcation of textures in ultramafc xenoliths. Journal of Geology, 85, 49-61.
27. Palandzhyan S.A. (1992) [Classifcation of mantle peridotites according to geodynamic settings]. Magadan, SVKNII DVO RAN 104 p. (in Russian)
    Piccardo G.B., Rampone E., Vannucci R (1990) Upper mantle evolution during continental rifting and ocean formation: evidence from peridotite bodies of the Western Alpine-Northern Apennine system, Mémoires de la Société géologique de France, 156, 323-333.
28. Popov V.A. (2011) [Practical genetic mineralogy] Yekaterinburg, UrO RAN, 167 p. (in Russian)
29. Pushkarev E.V., Kamenetsky V.S., Morozova A.V., Khiller V.V., Glavatskykh S.P., Rodemann T. (2015) Ontogeny of ore Cr-spinel and composition of inclusions as indicators of the pneumatolytic-hydrothermal origin of PGM-bearing chromitites from Kondyor massif, the Aldan Shield. Geology of Ore Deposits, 57, 352-380.
30. Rampone E., Piccardo G.B., Vannucci R, Bottazzi P., Ottolini L. (1993) Subsolidus reactions monitored by trace element partitioning: the spinel- to plagioclase-facies transition in mantle peridotites. Contributions to Mineralogy and Petrology, 115, 1-17.
31. Rampone E., Vissers R.L.M., Poggio M., Scambellu-ri M., Zanetti A. (2010). Melt migration and intrusion during exhumation of the Alboran lithosphere: the Tallante mantle xenolith record (Betic Cordillera, SE Spain). Journal of Petrology, 51, 295-325.
32. Ringwood A.E. (1975) Composition and Structure of the Earth´s Mantle. New York, McGraw-Hill. 618 p.
33. Risold A.-C, Trommsdorf V., Grobety B. (2001) Genesis of ilmenite rods and palisades along humite-type defects in olivine from Alpe Arami. Contributions to Mineralogy and Petrology, 140, 619-628.
34. Saveliev D.E. (2018) [Kraka ultramafc massifs (South Urals): features of structure and composition of peridotite-dunite-chromitite assemblages] Ufa, Bashkirskaya entsyklopedia, 304 p. (in Russian with English summary)
35. Saveliev D.E., Belogub E.V., Blinov I.A., Kozhevni-kov D.A., Kotlyarov V.A. (2016) [Petrological evidences of syndeformation segregation of chromites during dunite formation: example of Kraka ophiolites, South Urals]. Mineralogiya [Mineralogy], 2(4), 56-77. (in Russian)
36. Saveliev D.E., Shilovskikh V.V., Sergeev S.N. (2019) [Microstructural study of plastically deformed ultramafc rocks: traditional and current methods, implication for petrology]. Metallogeniya drevnikh i sovremennykh okeanov [Metallogeny of ancient and modern oceans]. Miass, IMin UrO RAN, 42–47. (in Russian)
37. Saveliev D.E., Sergeev S.N. (2018) [Enstatite from ophiolitic peridotites: plastic deformation and related chemical changes]. Mineralogiya [Mineralogy], 1(6), 68-84 (in Russian)
38. Saveliev D.E., Fedoseev V.B. (2019) Solid-state redistribution of mineral particles in upwelling mantle fow as a mechanism of chromite accumulation in ophiolitic ultramafc rocks (example of Kraka ophiolites, South Urals). Georesursy [Georesources], 21(1), 31-46. DOI: https://doi.org/10.18599/grs.2019.1.31-46
39. Savelieva G.N. (1987) [Gabbro-ultramafc complexes of the Uralian ophiolites and their analogs in the present-day oceanic crust]. Moscow, Nauka, 230 p. (in Russian)
40. Shimizu Y, Arai S., Morishita T., Ishida Y (2008) Origin and signifcance of spinel-pyroxene symplectite in lherzolite xenoliths from Tallante, SE Spain. Mineralogy and Petrology, 94, 27-43.
41. Stoll W.C. (1958) Geology and petrology of the Masinloc chromite deposit, Zambales, Luzon, Philippine islands. Bulletin of the Geological Society of America, 89, 410-448.
42. Yudovskaya M.A., Costin G, Shilovskikh V, Chaplygin I., McCreesh M., Kinnaird J. (2019) Bushveld symplectic and sieve textured chromite is a result of coupled dissolution-reprecipitation: a comparison with xenocrystic chromite reactions in arc basalt. Contributions to Mineralogy and Petrology, 174, 74.
43. Shumikhin E.A. (1980) [Unpublished report on results of survey of disseminated chromites at the Nurali massif] Ufa, BTGU.
    Zhabin A.G. (1979) [Ontogeny of crystals. Aggregates] Moscow: Nauka, 276 p. (in Russian)
44. Zwang RY, Su J.F., Mao H.K., Liou J.G (1999) Magnetite lamellae in olivine and clinogumite from Dabie UHP ultramafc rocks, Central China. American Mineralogist, 84, 564-569.