УДК 552.321.6 (470.5)



The purpose of work: estimation of the ratio of magmatic and metasomatic processes during the formation of dunites in arrays of folded areas. The relevance of the work is due to the need to adjust the legend during geological mapping and when searching for chromite ores.
Methodology of the work: generalization of a long-term study of the geological structure, mineralogy, petrochemistry, and geochemistry of chromitebearing ultramafites of the Urals with the involvement of world petrological and experimental data. Results. The mantle ultramafic rocks are represented by two main types – subcontinental and ophiolitic ones. Dunites are developed in both types. Dunites in the subcontinental ultramafites are exposed in the most eroded parts of massifs. Contacts with overlying harzburgites and lherzolites are gradual, which implies the formation of the entire incision during a nonrecurrent process with the formation of a single dunite-harzburgite-lherzolite series. The process responsible for its formation was the partial melting of pyrolite of the mantle, as evidenced by the results of experiments confirmed by the published data studying the composition of rock-forming ultramafite minerals. Dunites should be considered as the final product of the process of partial melting of pyrolite mantle. Dunites of ophiolites have a fundamentally different nature; they are formed according to restites, products of partial melting, and they are part of two complexes: websterite-dunite and gabbro-clinopyroxenite-dunite. Dunites of the first complex are formed during the synkinematic metamorphic differentiation of restites; dunites of the second complex – as a result of the reaction of gabbro with restites.
Conclusion. Three genetic types of dunites take part in the structure of mantle ultramafites of folded areas: 1) products of partial melting of mantle pyrolite, 2) products of synkinematic metamorphic differentiation of harzburgites, 3) products of the reaction of gabbroids with harzburgites. The association of the first type with subcontinental ultramafites and the rest with ophiolites indicates the different geodynamic setting for the formation of ultramafites and the associated chromite concentrations: unique deposits of high-chromous ores occur in subcontinental ultramafites; numerous small ore occurrences of medium-chrome ores – in ophiolites.

Keywords: dunite, partial melting, pyrolyte, restite, subcontinental ultramafites, ophiolite.

The work was performed within the framework of the state assignment of the Institute of geology and geochemistry of the Ural Branch of the Russian Academy of Sciences (state registration number AAA-A18-118052590026-5).



1. Den Tex E. 1969, Origin of ultramafi c rocks, their tectonic setting and history: A contribution to the discussion of the paper «The origin of ultramafi c and ultrabasic rocks» by P. J. Wyllie. Tectonophysics, vol. 7, pp. 457–488. https://doi.org/10.1016/0040-1951(69)90016-X

2. Ringwood A. Е. 1981, Composition and petrology of the earth’s mantle. Moscow, 584 p.

3. Kelemen P., Dick H. J. B., Quick J. 1992, Formation of harzburgite by pervasive melt/rock reaction on the upper mantle. Nature, vol. 358, pp. 635–641. https://doi.org/10.1038/358635a0

4. Van der Wal D., Bodinier J.-L. 1996, Origin of the recrystallization front in the Ronda peridotite by km-scale pervasive porous melt fl ow. Contrib. Mineral. Petrol, vol. 122, pp. 387–405. https://doi.org/10.1007/s004100050135

5. Barth M. G., Mason P. R. D., Davies G. R., Dijkstra A. H., Drury M. R. 2003, Geochemistry of the Othris Ophiolite, Greece: Evidence for Refertilization? J. Petrol, vol. 44, no. 10, pp. 1759–1785. https://doi.org/10.1093/petrology/egg058

6. Lenoir X., Garrrido C. J., Bodinier J.-L. et al. 2001, The Recrystallization Front of the Ronda Peridotite: Evidence for Melting and Thermal Erosion of Subcontinental Lithospheric Mantle beneath the Alboran Basin. J. Petrol, vol. 42, no. 1, pp. 141–158.

7. Dijkstra A. H., Barth M. G., Drury et al. 2003, Diffuse porous melt and melt-rock reaction in the mantle lithosphere at a slow-spreading ridge: A structural petrology and LA-ICP-MS study of the Othris Peridotite Massif (Greece). Geochemistry, Geophysics, Geosystem, vol. 4, issue 24. https://doi.org/10.1029/2001GC000278

8. Le Roux V., Bodinier J.-L., Tommasi A., Alard O. et al. 2007, The Lherz spinel lherzolite: Refertilized rather than pristine mantle. Earth Planet. Sci. Lett, vol. 259, pp. 599–612. http://dx.doi.org/10.1016/j.epsl.2007.05.026

9. Chashchukhin I. S., Votyakov S. L., Shchapova Yu. V. 2007, Kristallokhimiya khromshpineli i oksitermobarometriya ul’tramafi tov skladchatykh oblastey [Crystal chemistry of spinel and oxytermobarometry of ultramafi tes of folded regions]. Ekaterinburg, 310 p.

10. Takazawa E., Frey F. A., Shimizu N., Obata M. 2000, Whole rock compositional variations in an upper mantle peridotite (Horoman, Hokkaido, Japan): Are they consistent with a partial melting process? Geochim. Cosmochim. Acta, vol. 64, no. 4, pp. 695–716. https://doi.org/10.1016/ S0016-7037(99)00346-4

11. Jaques A. L., Green D. H. 1980, Anhydrous melting of peridotite at 0–15 kb pressure and genesis of tholeiitic basalts. Contrib. Mineral. Petrol., vol. 73, no. 3, pp. 287–310. https://doi.org/10.1007/BF00381447

12. Gaetani G. A., Grove T. L. 1998, The infl uence of water on melting of mantle peridotite. Contrib. Mineral. Petrol., vol. 131, pp. 323–346. https:// doi.org/10.1007/s004100050396

13. Niida K., Green D. H. 1999, Stability and chemical composition of pargasitic amphibole in MORB pyrolite under upper mantle conditions. Contrib. Mineral. Petrol., vol.135, pp. 18–40. https://doi.org/10.1007/s004100050495

14. Arai S. 1994, Characterization of spinel peridotites by olivine-spinel compositional relationships: Review and interpretation. Chemical Geology, vol. 113, pp. 191–204. https://doi.org/10.1016/0009-2541(94)90066-3

15. Downes H. 2001, Formation and Modifi cation of the Shallow Sub-continental Lithospheric Mantle: a Review of Geochemical Evidence from Ultramafi c Xenolith Suites and Tectonically Emplaced Ultramafi c Massifs of Western and Central Europe. J. Petrol., vol. 42, no. 1, pp. 233–250. https://doi.org/10.1093/petrology/42.1.233

16. Niu Y. 2004, Bulk-rock Major and Trace Element Compositions of Abyssal Peridotites: Implications for Mantle Melting, Melt Extraction and Post-melting Processes Beneath Mid-Ocean Ridges. J. Petrol., vol. 45, no. 12, pp. 2423–2458. https://doi.org/10.1093/petrology/egh068

17. Palme H., Nickel K. G. 1985, Ca:Al ratio and composition of the Earth, supper mantle. Geochim. Cosmochim. Acta, vol. 49, no. 10, pp. 2123–2132. https://doi.org/10.1016/0016-7037(85)90070-5

18. Frey F. A., Suen C. J., Stockman H. W. 1985, The Ronda high temperature peridotite: Geochemistry and petrogenesis. Geochim. Cosmochim. Acta, no. 49, pp. 2469–2491. https://doi.org/10.1016/0016-7037(85)90247-9

19. Falloon T. J., Green D. Y. 1987, Anhydrous partial melting of MORB pyrolite and other peridotite compositions at 10 kb: implications for the origin of primitive MORB glasses. Mineral Petrol., vol. 37, pp. 181–219.

20. Hofmann A. W. 1988, Chemical differentiation of the Earth: the relationship between mantle, continental crust, and oceanic crust. Earth Planet. Sci. Lett., vol. 90, pp. 297–314. https://doi.org/10.1016/0012-821X(88)90132-X

21. Ringwood A. E. 1991, Phase transformation and their bearing on the constitution and dynamics of the mantle. Geochim. et Cosmochim. Acta, no. 55. pp. 2083–2110. http://dx.doi.org/10.1016/0016-7037(91)90090-R

22. Allegre C. J., Poirier J. P., Humler E., Hoffman F. W. 1995, The chemical composition of the Earth. Earth Planet. Sci. Lett., vol. 134, pp. 515–526.

23. McDonough W. F., Sun S.-S. 1995, The composition of the Earth. Chem. Geol., vol. 120, pp. 223–253. https://doi.org/10.1016/0009-2541(94)00140-4

24. Savelyev A. A., Savel’eva G. N. 1977, Voykaro-Syn’inskiy massiv / Petrologiya i metamorfizm drevnikh ofiolitov (na primere Polyarnogo Urala i Zapadnogo Sayana) [Voikar-Syninsky massif. Petrology and metamorphism of ancient ophiolites (using the Polar Urals and the Western Sayan as an example)]. Novosibirsk, pp. 60–91.

25. Bonatti E., Ottonello G., Hamlyn P. R. 1986, Peridotites from the island of Zabargad (St. John), Red Sea: Petrology and geochemistry. J. Geophys. Res., vol. 91, pp. 599–631. https://doi.org/10.1029/JB091iB01p00599

26. Barth M. G., Mason P. R. D., Davies G. R., Drury M. R. 2008, The Othris Ophiolite, Greece: A snapshot of subduction initiation at a mid-ocean ridge. Lithos., vol. 100, pp. 234–254. https://doi.org/10.1016/j.lithos.2007.06.018

27. Loney R. A., Himmelberg G. R., Coleman R. G. 1971, Structure and petrology of the alpine-type peridotite at Burro Mountain, California, U. S. A. J. Petrol., vol. 12, part 2, pp. 245–309. https://doi.org/10.1093/petrology/12.2.245


Лицензия Creative Commons
All articles posted on the site are available under the Creative Commons Attribution 4.0 Global License.