THERMOMAGNETIC ANALYSIS OF ULTRAMAFIC ROCKS: A CASE STUDY OF DUNITE FROM THE PEKUL'NEY COMPLEX, CHUKOTKA, NE RUSSIA
Аннотация и ключевые слова
Аннотация (русский):
Petromagnetic and thermomagnetic properties of 13 dunite samples from the Pekul'ney Complex in the central Chukotka Peninsula, NE Russia, were measured to gain insight into the potentialities of thermomagnetic techniques in application to studying ultramafic rocks. Dunite currently found in layered tabular ultramafite bodies was produced in the lower crust beneath island arcs or oceanic volcanic arcs and now occurs in tectonic blocks a few kilometers across in the mélange in the axial part of the Pekul'ney Range, which marks the boundary between volcanic complexes. When exhumed, the dunite was affected by a number of episodes of prograde metamorphism, which were associated with the crystallization of metamorphic spinel and magnetite in these rocks. Our data confirm that the temperatures of kinks on the thermomagnetic curves of the natural remanent magnetization of the rocks $I_{n}(T)$ reflect the temperatures of the metamorphic episodes during which ferromagnetic minerals crystallized. Within the range of the possible comparison of temperature estimates obtained for metamorphic recrystallization using magnetic and petrologic techniques (approximately 400--600° C), these estimates for dunite show reasonably good consistence. It is established that the ferromagnetic mineral that crystallized during two metamorphic episodes of the dunite at 530--580 and 400--460° C was low-Cr magnetite. Our data do not indicate that metamorphic spinel can any significantly contribute to the integral magnetization of the rocks. In addition to the two aforementioned episodes of metamorphic recrystallization, our thermomagnetic data on the dunite suggest metamorphic episodes within the temperature ranges of 250--280 and 170--200° C. Data obtained in the course of this study are the first to prove simultaneous crystallization of metamorphic Cr-spinel and magnetite whose compositions were not in thermodynamic equilibrium during certain episodes of medium-temperature metamorphic recrystallization of the ultramafic rock, which can be explained by the very low mobility of Cr in the course of metamorphism.

Ключевые слова:
Serpentinization, medium-temperature metamorphism, ferrite-chromite, thermomagnetic curves, geothermometer, solid solution, Curie temperature, metamorphic recrystallization
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Список литературы

1. Ballhaus, C., Berry, R. F., Green, D. H. High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: implications for the oxidation state of the upper mantle, // Contrib. Mineral. Petrol., 1991. - v. 107 - p. 27.

2. Bazylev, B. A. Allochemical metamorphism of mantle peridotites in the Hayes Fracture Zone of the North Atlantic, // Petrology, 1997. - v. 5 - no. 4 - p. 322.

3. Bazylev, B. A. Awaruite containing mineral association abundance in peridotite of the fault zone 15°20' (the Atlantic ocean) as one of the manifestations of oceanic metamorphism, // Russ. J. Earth Sci., 2000. - v. 2 - no. 3 - p. 279.

4. Bazylev, B. A. Petrology and geochemistry of oceanic and Alpine-type spinel peridotites in the context of the problem of mantle material evolution - Moscow: Vernadsky Institute of Geochemistry and Analytical Chemistry (GEOKHI), Russian Academy of Sciences., 2003.

5. Bazylev, B. A., Ledneva, G. V., Kononkova, N. N., Ishiwatari, A. High-pressure ultramafics in the lower crustal rocks of the Pekul'ney Complex, central Chukchi Peninsula. 1. Petrography and mineralogy, // Petrology, 2013a. - v. 21 - no. 3 - p. 221.

6. Bazylev, B. A., Ledneva, G. V., Ishiwatari, A. High-pressure ultramafics in the lower crustal rocks of the Pekul'ney Complex, central Chukchi Peninsula. 2. Internal structure of blocks and ultramafic bodies, geologic and geodynamic setting of rock formation, // Petrology, 2013b. - v. 21 - no. 4 - p. 336.

7. Bazylev, B. A., Popov, K. V., Shcherbakov, V. P. Petrographic features of oceanic peridotites as reflected by their magnetic characteristics, // Russ. J. Earth Sci., 2002. - v. 4 - p. 211.

8. Bazylev, B. A., Silantyev, S. A., Kononkova, N. A Metamorphism of hyperbasites in the oceanic crust // Magmatism and Tectonics of the Ocean (Lithos Project) - Moscow: Nauka., 1990. - p. 296.

9. Dunlop, D. J., Prevot, M. Magnetic properties and opaque mineralogy of drilled submarine intrusive rocks, // Geophys. J. R. Astr. Soc., 1982. - v. 69 - p. 763.

10. Kadzialko-Hofmokl, M., Delura, K., Bylina, P., Jelenska, M., Kruczyk, J. Mineralogy and magnetism of Fe-Cr spinel series minerals from podiform chromitites and dunites from Tapadla (Sudetic ophiolite, SW Poland) and their relationship to palaeomagnetic results of the dunites, // Geophys. J. Int., 2008. - v. 175 - p. 885.

11. Kudryavtseva, G. P. Ferrimagnetism of Natural Oxides - Moscow: Nedra., 1988. - 232 pp.

12. Nazarova, E. A., Wasilewski, P. J., Dick, H. J. Magnetic study of serpentinized harzburgites from the Islas Orcadas Fracture Zone, // Mar. Geophys. Res., 2000. - v. 21 - no. 5 - p. 475.

13. Nguen Thi Kim, Thoa, Pecherskii, D. M. Serpentinites: A likely source of magnetic lineations, // Izv. Akad. Nauk SSSR, Ser. Geol., 1989. - v. 1 - p. 61.

14. Popov, K. V., Bazylev, B. A., Shcherbakov, V. P. Temperature range for magnetization of oceanic spinel peridotites, // Oceanology, 2006. - v. 46 - no. 2 - p. 61.

15. Popov, K. V., Bazylev, B. A., Shcherbakov, V. P., Gapeev, A. K. Comparison between the magnetic and petrological characteristics of the peridotites from the gorringe ridge and the peridotites from the Mid-Ocean Ridges, // Oceanology, 2011. - v. 51 - no. 1 - p. 157.

16. Popov, K. V., Shcherbakov, V. P. Petromagnetic characteristics of oceanic crustal rocks. Serpentinite // Nature of Magnetic Anomalies and the Inner Structure of the Oceanic Crust - Moscow: VNIRO., 1996. - p. 157.

17. Readman, P. W., O'Reilly, W. Magnetic properties of oxidized (cation-deficient) titanomagnetites $\mathrm{(Fe, Ti)_3O_4}$, // J. Geomagn. Geoelectr., 1972. - v. 24 - p. 69.

18. Robbins, M., Wertheim, G. K., Sherwood, R. C., et al. Magnetic properties and site distributions in the system[linebreak] $\mathrm{FeCr_2O_4 - Fe_3O_4(Fe_2 + Cr_2-xFex_3+O_4)}$, // J. Phys. Chem. Solids, 1971. - v. 32 - p. 717.

19. Sack, R. O., Ghiorso, M. S. Chromian spinels as petrogenetic indicators: thermodynamic and petrologic applications, // American Mineralogist, 1991. - v. 76 - p. 827.

20. Shcherbakov, V. P., Lamash, B. E., Shcherbakova, V. V. The nature of magnetization of oceanic crustal rocks // The Nature of Magnetic Anomalies and the Structure of Oceanic Crust - Moscow: All-Russia Research Institute of Fishery and Oceanography., 1996. - p. 7.

21. Shcherbakova, V. V., Shcherbakov, V. P., Vinogradov, Yu. K. pTRM properties as a function of the grain size and their manifestations in paleomagnetic experiments, // Geophys. Stud., 2008. - v. 9 - no. 4 - p. 5.

22. Thellier, B., Thellier, O. Sur l'intensite du champ magnetique terrestre dans le passe, historique et geologique, // Ann. Geophys., 1955. - v. 15 - p. 285.

23. Ziemniak, S. E., Castelli, R. A. Immiscibility in the $\mathrm{Fe_3O4-FeCr_2O_4}$ spinel binary, // J. Phys. Chem. Solids, 2003. - v. 64 - p. 2081.

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