A large data base of 1821 chromian spinel compositions Cr2O3 gt; 2 wt% in ultramafic nodules from basalts, kimberlites, lamproites, ultramafic massifs, and from the diamond assemblage has been analyzed using mathematical statistics methods. For each spinel component under study TiO2, Al2O3, Cr2O3, FeO, MnO, MgO, a considerable overlap is observed, spinels with the highest Cr-number #Cr being found in the diamond assemblage and those with the highest Mg-number #Mg, in nodules from basalts. The lowest oxidation degree is detected in spinels from nodules in basalts and from the diamond assemblage. Spinels from ultramafic massifs have the highest oxidation degrees and Fe-numbers. In ultramafic massifs from kimberlite to lamproite through to the diamond type, spinel compositions follow the same variation trends. Spinels from the basaltic group fall away from these trends. Compositional variability of spinels is due chiefly to isomorphic replacement of Fe+2 for Mg and of Al and Mg for Cr. Kimberlite-type spinels have high and broadly variable Ti contents. Igneous and metamorphic/metasomatic origins for spinels of the five groups under study are discussed. Spinel compositions from ultramafic rocks found in continental structures are shown to indicate that at depth beneath these structures, there exist physicochemical conditions for crystallization inherent to all the principal tectonic features of the earth-continents, oceans, and transition zones island arcs.
classification of chromian spinels, deep-seated rocks, continental structures, kimberlites.
1. Afanasiev, 7 Int. Kimberlite Conf., Extend. Abstracts, v. 7-8, 1998.
2. Agrell, Proc. Apollo 11 Lunar Sci. Conf., v. 1, 1970.
3. Bagdasarov, Composition and properties of deep-seated crustal and upper mantle rocks of gratons, 1983.
4. Bagdasarov, All-Union Symposium on Mantle Nodules and the Issues of Ultramafic Magmas, abstract, 1980.
5. Bagdasarov, Zap. Vses. Mineral. O-va, v. 106, no. 5, 1979.
6. Basu, Geochim. Cosmochim. Acta, v. 39, no. 6/7, 1975., doi:https://doi.org/10.1016/0016-70377590039-3
7. Bazylev, Geokhimiya, v. 7, 1995.
8. Bazylev, Petrologiya, v. 6, no. 4, 1998.
9. Bobrievich, Petrography and Mineralogy of Kimberlitic Rocks of Yakutia, 1964.
10. Borovikov, Statistica: Statistics Analysis and Data Processing in Windows Environment, 1997.
11. Bushueva, Data Banks, Chemical Characteristics, and Classification of Spinellids from Kimberlites, 1991.
12. Dawson, Kimberlites and Their Xenoliths, 1980.
13. Dick, Contrib. Mineral. Petrol., v. 86, no. 1, 1984., doi:https://doi.org/10.1007/BF00373711
14. Fipke, Kimmberlites, Related Rocks and Mantle Xenoliths, SPRM Spec. Publ., v. 1A, no. 1, 1994.
15. Garanin, 7th Conf. of Young Scientists Geochemistry and Mineral Deposits, 1980.
16. Genshaft, Fiz. Zemli, no. 10, 1993.
17. Genshaft, Properties and State of Mineral Matter in the Earth's Interior, 1989.
18. Hill, J. Petrol., v. 82, no. 6, 1974.
19. Ilupin, Geokhimiya, v. 6, 1997.
20. Irvine, Canad. J. Earth Sci., v. 4, 1967.
21. Matsyuk, Spinellids of Mantle Rocks, 1989.
22. Ozawa, Contrib. Mineral. Petrol., v. 82, no. 1, 1983., doi:https://doi.org/10.1007/BF00373711
23. Palandzhyan, Dokl. Akad. Nauk SSSR, v. 307, no. 3, 1989.
24. Paneyakh, Continental Crust in Space and Time: Magmatism, 1989.
25. Poroshin, Geol. Geofiz., v. 8, 1988.
26. Prikhodko, Geol. Geofiz., v. 7, 1980.
27. Pustotsvetov, Geokhimiya, no. 10, 1992.
28. Rasskazov, Min. Zhurnal, v. 9, no. 6, 1987.
29. Roeder, Canad. Mineral., v. 32, no. 4, 1994.
30. Sack, Am. Mineral., v. 76, 1991.
31. Sobolev, Deep-seated Inclusions in Kimberlites and the Issue of Upper Mantle Composition, 1974.
32. Sobolev, Geol. Geofiz., v. 11, 1975.
33. Vaganov, Rudy i Metally, v. 3, 1999.
34. Young, Geosci. J., v. 3, no. 1, 1999., doi:https://doi.org/10.1023/A:1011574824970
35. Zhelyazkova-Panayotova, Mineral. Soc. Japan. Spec. Pap., v. 1, 1971.
