PETROGENESIS OF POST-ACCRETIONARY GRANITES OF THE KIZIL COMPLEX, SOUTHERN URALS: GEOCHEMISTRY, Sr-Nd ISOTOPIC DATA, U-Pb AGE

The Late Devonian – Early Carboniferous intrusive magmatism in the West Magnitogorsk zone of the Southern Urals is associated with post-island arc restruction of the earth’s crust during the assembly of the Laurasia supercontinent. Magmatic bodies usually have a submeridional orientation, and the rocks are compositionally variegated and display mixed geochemical characteristics of supra-subduction and intraplate magmatism. A small proportion of magmatism falls within plagiogranites, the earliest of which correspond to the Kizil complex, which records the continental-type crust formation at the base of the Magnitogorsk island-arc terrane. It has been found that thin dikes and sills of the Kizil complex occur widely in the central part of the West Magnitogorsk zone and are represented by metasomatized plagiogranites with wide variations in alumina content (12–18 %), iron content (Fe# 0.7–0.9) and total REE (117–347 ppm). The ID TIMS method yielded four U-Pb zircon ages of which the 345±6 Ma value agrees most satisfactorily with the geological data; other values may be associated with the assimilation of host rocks and metasomatism of granites. Based on the microelement (variable minimums for Eu and Sr, minimums for Ti, Nb and Ta) and isotopic composition of Sr, Nd (εNd₍₃₄₅₎=5.9–6.0, ⁸⁷Sr/⁸⁶Sr₍₃₄₅₎=0.7041–0.7051), it was concluded that that the main source of the Kizil granitoids could be amphibolized mafic rocks of the ophiolite association, thrust onto the margin of the Laurussia paleocontinent along the Main Ural Fault zone to the west of the West Magnitogorsk zone.

1. Acosta-Vigil A., London D., Morgan G.B., Dewers T.A., 2003. Solubility of Excess Alumina in Hydrous Granitic Melts in Equilibrium with Peraluminous Minerals at 700–800 °C and 200 MPa, and Applications of the Aluminum Saturation Index. Contributions to Mineralogy and Petrology 146, 100–119. https://doi.org/10.1007/s00410-003-0486-6.

2. Azovskova O.B., Soroka E.I., Rovnushkin M.Yu., Soloshenko N.G., 2020. Sm-Nd Isotopy of the Dykes of the Vorontsovskoe Gold-Ore Deposit (Northern Urals). Vestnik of Geosciences 9, 3–6 (in Russian). https://doi.org/10.19110/geov.2020.9.1.

3. Blichert-Toft J., Puchtel I.S., 2010. Depleted Mantle Sources Through Time: Evidence from Lu-Hf and Sm-Nd Isotope Systematics of Archean Komatiites. Earth and Planetary Science Letters 297 (3–4), 598–606. https://doi.org/10.1016/j.epsl.2010.07.012.

4. Bouvier A., Vervoort J.D., Patchett P.J., 2008. The Lu-Hf and Sm-Nd Isotopic Composition of CHUR: Constraints from Unequilibrated Chondrites and Implications for the Bulk Composition of Terrestrial Planets. Earth and Planetary Science Letters 273 (1–2), 48–57. https://doi.org/10.1016/j.epsl.2008.06.010.

5. Boynton W.V., 1984. Cosmochemistry of the Rare Earth Elements: Meteorite Studies. Developments in Geochemistry 2, 63–114. https://doi.org/10.1016/B978-0-444-42148-7.50008-3.

6. Brown D., Spadea P., Puchkov V., Alvarez-Marron J., Herrington R., Willner A.P., Hetzel R., Gorozhanina Y., Juhlin C., 2006. Arc–Continent Collision in the Southern Urals. Earth-Science Reviews 79 (3–4), 261–287. https://doi.org/10.1016/j.earscirev.2006.08.003.

7. Faure G., 1989. Fundamentals of Isotope Geology. Mir, Moscow, 590 p. (in Russian).

8. Frost B.R., Barnes C.G., Collins W.J., Arculus R.J., Ellis D.J., Frost C.D., 2001. A Geochemical Classification for Granitic Rocks. Journal of Petrology 42 (11), 2033–2048. https://doi.org/10.1093/petrology/42.11.2033.

9. Harris N.B.W., Pearce J.A., Tindle A.G., 1986. Geochemical Characteristics of Collision-Zone Magmatism. Geological Society of London Special Publications 19, 67–81. https://doi.org/10.1144/GSL.SP.1986.019.01.04.

10. Hughes C.J., 1972. Spilites, Keratophyres, and the Igneous Spectrum. Geological Magazine 109 (6), 513–527. https://doi.org/10.1017/S0016756800042795.

11. Hutchison C.S., 1974. Laboratory Handbook of Petrographic Techniques. John Wiley & Sons, New York, 527 p.

12. Hutchison C.S., 1975. The Norm, Its Variations, Their Calculation and Relationships. Schweizerische Mineralogische und Petrographische Mitteilungen 55, 243–256.

13. Ivanov K.S., Smirnov V.N., Erokhin Yu.V., 2000. Collisional Tectonics and Magmatism (Using the Middle Urals as an Example). IGG UB RAS, Ekaterinburg, 131 p. (in Russian).

14. Krogh T.Е., 1973. A Low-Contamination Method for Hydrothermal Decomposition of Zircon and Extraction of U and Pb for Isotopic Age Determinations. Geochimica et Cosmochimica Acta 37 (3), 485–494. https://doi.org/10.1016/0016-7037(73)90213-5.

15. Large R.R., Gemmell J.B., Paulick H., Huston D.L., 2001. The Alteration Box Plot: A Simple Approach to Understanding the Relationship Between Alteration Mineralogy and Lithogeochemistry Associated with Volcanic-Hosted Massive Sulfide Deposits. Economic Geology 96 (5), 957–971. https://doi.org/10.2113/gsecongeo.96.5.957.

16. Ludwig K.R., 1991. PbDat 1.21 for MS-DOS: A Computer Program for IBM-PC Compatibles for Processing Raw Pb-U-Th Isotope Data. Version 1.07. USGS Open File Report, 35 p.

17. Ludwig K.R., 2012. ISOPLOT 3.75. A Geochronological Toolkit for Microsoft Excel. User’s Manual. Berkeley Geochronology Center Special Publication 5, 75 p.

18. Maslov V.A., Artyushkova O.V., 2010. Stratigraphy and Correlation of Devonian Deposits of the Magnitogorsk Megazone of the South Urals. DesignPolygraphService, Ufa, 288 p. (in Russian).

19. Middlemost E.A.K., 1994. Naming Materials in the Magma/Igneous Rock System. Earth-Science Reviews 37 (3–4), 215–224. https://doi.org/10.1016/0012-8252(94)90029-9.

20. Pearce J.A., Harris N.B.W., Tindle A.G., 1984. Trace Element Discrimination Diagrams for the Tectonic Interpretation of Granitic Rocks. Journal of Petrology 25 (4), 956–983. https://doi.org/10.1093/petrology/25.4.956.

21. Puchkov V.N., 2010. Geology of the Urals and For-Urals (Actual Topics of Stratigraphy, Tectonics and Metallogeny). Uralian Geological Journal 3, 80–84 (in Russian).

22. Rakhimov I.R., Ankusheva N.N., Samigullin A.A., Shanina S.N., 2023. Origin and Evolution of Ore-Forming Fluids at the Small-Sized Gold Deposits in the Khudolaz Area, Southern Urals. Minerals 13 (6), 781. https://doi.org/10.3390/min13060781.

23. Rakhimov I.R., Samigullin A.A., 2024. Geochemistry of the Amphibolites Associated with the Ophiolite Massif of the Urals on the Example of the Rai-Is and Middle Kraka as a Key to Unravelling of Their Origin. Proceedings of Voronezh State University. Series: Geology 4, 35–50 (in Russian).

24. Rollinson H.R., 1993. Using Geochemical Data: Evaluation, Presentation, Interpretation. Longman Scientific & Technical, London, 352 p. https://doi.org/10.4324/9781315845548.

25. Salikhov D.N., Berdnikov P.G., 1985. Late Proterozoic Magmatism and Mineralization of the Magnitogorsk Megasynclinorium. Bashkir Branch of the USSR Academy of Sciences, Ufa, 94 p. (in Russian).

26. Salikhov D.N., Kholodnov V.V., Puchkov V.N., Rakhimov I.R., 2019. The Late Paleozoic Magnitogorsk Zone in the Southern Urals: Magmatism, Fluid Flow Regime, Metallogeny, and Geodynamics. Nauka, Moscow, 392 p. (in Russian).

27. Salikhov D.N., Pshenichny G.N., 1984. Magmatism and Mineralization in the Early Consolidation Zone of the Magnitogorsk Megasynclinorium. Bashkir Branch of the USSR Academy of Sciences, Ufa, 112 p. (in Russian).

28. Salikhov D.N., Rakhimov I.R., Moseichuk V.M., 2013. Carboniferous Collisional Magmatism in the Southern Urals. Geological Collection 10, 176–199 (in Russian).

29. Scarrow J.H., Spadea P., Cortesogno L., Savelieva G.N., Gaggero L., 2000. Geochemistry of Garnet Metagabbros from the Mindyak Ophiolite Massif, Southern Urals. Ofioliti 25 (2), 103–115. DOI:10.4454/ofioliti.v25i2.118.

30. Schnetzler C.C., Philpotts J.A., 1968. Partition Coefficients of Rare-Earth Elements and Barium Between Igneous Matrix Material and Rock-Forming Mineral Phenocrysts–I. In: L.H. Ahrens (Ed.), Origin and Distribution of the Elements. Pergamon Press, Oxford, New York, p. 929–938. https://doi.org/10.1016/B978-0-08-012835-1.50076-3.

31. Schnetzler C.C., Philpotts J.A., 1970. Partition Coefficients of Rare-Earth Elements Between Igneous Matrix Material and Rock-Forming Mineral Phenocrysts–II. Geochimica et Cosmochimica Acta 34 (3), 331–340. https://doi.org/10.1016/0016-7037(70)90110-9.

32. Seravkin I.B., Znamensky S.E., Kosarev A.M., 2001. Fault Tectonics and Ore Deposits of the Trans-Uralian Bashkiria. Ufa Poligrafcombinat, Ufa, 318 p. (in Russian).

33. Shand S.J., 1943. Eruptive Rocks: Their Genesis, Composition, and Classification, with a Chapter on Meteorites. Second Edition. John Wiley & Sons, New York, 444 p.

34. Stacey J.T., Kramers J.D., 1975. Approximation of Terrestrial Lead Isotope Evolution by a Two-Stage Model. Earth and Planetary Science Letters 26 (2), 207–221. https://doi.org/10.1016/0012-821X(75)90088-6.

35. State Geological Map of the Russian Federation, 2015. South Ural Series. Scale of 1:200000. Sheet N-40-XXIX (Sibay). Explanatory Note. Moscow Branch of VSEGEI, Moscow, 218 p. (in Russian).

36. Steiger R.H., Jäger E., 1977. Subcommission on Geochronology: Convention on the Use of Decay Constants in Geo- and Cosmochronology. Earth and Planetary Science Letters 36 (3), 359–362. https://doi.org/10.1016/0012-821X(77)90060-7.

37. Sun S.-S., McDonough W.F., 1989. Chemical and Isotopic Systematics of Oceanic Basalts: Implications for Mantle Composition and Processes. Geological Society of London Special Publications 42 (1), 313–345. https://doi.org/10.1144/GSL.SP.1989.042.01.19.

38. Sylvester P.J., 1989. Post-Collisional Alkaline Granites. Journal of Geology 97 (3), 261–280. https://doi.org/10.1086/629302.

39. Turkina O.M., 2000. Modeling Geochemical Types of Tonalite–Trondhjemite Melts and Their Natural Equivalents. Geochemistry International 38 (7), 640–651.

40. Vishnevskaya I.A., 2018. Isotopic and Geochemical Characteristics of Cambrian Phosphorites of Karatau Basin (Southern Kazakhstan). Vestnik of SPU. Earth Sciences 63 (3), 267–290 (in Russian). https://doi.org/10.21638/spbu07.2018.302.

41. Watson E.B., Harrison T.M., 1983. Zircon Saturation Revisited: Temperature and Composition Effects in a Variety of Crustal Magma Types. Earth and Planetary Science Letters 64 (2), 295–304. https://doi.org/10.1016/0012-821X(83)90211-X.

42. Xiong X.L., Adam J., Green T.H., 2005. Rutile Stability and Rutile/Melt HFSE Partitioning During Partial Melting of Hydrous Basalt: Implications for TTG Genesis. Chemical Geology 218 (3–4), 339–359. https://doi.org/10.1016/j.chemgeo.2005.01.014.

43. Zakharov O.A., Tkachev S.A., 1984. Study of the Location Patterns of Intrusion-Related Endogenous Mineralization of the Khudolaz Syncline to Direct Exploration Towards Copper-Nickel and Other Ores (From the Materials Collected by the East-Ural Party During 1982–1984). Report. Vol. 1. Ufa, 148 p. (in Russian).

44. Znamensky S.E., 2009. Structural Conditions of Formation of Collision Gold Deposits of the Eastern Slope of the Southern Urals. Gilem, Ufa, 345 p. (in Russian).