The origin of the low density zones in the crystalline crust of the Transcarpathian depression (Ukraine) from petrophysical thermobaric modelling
Received: March 04, 2020
Subbotin Institute of geophysics of National Academy of Sciences of Ukraine
Subbotin Institute of Geophysics, NAS of Ukraine
Subbotin Institute of Geophysics, NAS of Ukraine
Subbotin Institute of geophysics of National Academy of Sciences of Ukraine

Purpose. Based on laboratory PT-studies of rocks and their joint analysis with the data from the regional profile RP-17, the aim of this research is to reveal the origin of the low-velocity zones in the Transcarpathian depression as zones of thermobaric rock decompaction and to elucidate the relationship of these zones with earthquakes and hydrocarbon fields. Methodology. The essence of such an approach is the comparison of the DSS information with experimental data on the physical parameters of rocks at high pressures and temperatures. For this purpose, we used the results e from high PT measurements of physical parameters on rocks analogous to those from the region under study. Results. Having analyzed the findings   of the laboratory PT-experiments, we developed the method of petrophysical thermobaric modelling.   This method is based on the characteristics of the “granitoid” type rocks from the Ukrainian Shield and the results of the joint interpretation of these data and information on the regional deep seismic sounding profiles from this tectonic unit. These approaches and techniques were applied to the analysis of the data from Transcarpathia, in particular, to the RP-17 regional profile. Two decompaction zones of the thermobaric origin were revealed along the profile coinciding with low seismic velocity zones. They are supposed to be effective regional traps for the mantle fluids, especially for hydrocarbons which under high pressure, temperature, and decompression penetrate into the near-surface layers of the sedimentary cover and form mineral deposits. In the decompaction zones shallow earthquakes with low magnitudes become activated. They widen the decomposition domains and facilitate the movement of deep hydrocarbons to the  location within them. Originality. For the first time, it was shown that low velocity zones (the region of thermobaric decompaction of mineral matter) under certain pressure and temperature in the Еarth's crust of “thermoactive” region, including Transcarpathia, are its integral part; they are inevitably formed in the process of warming up of the Earth’s interior during its “thermoactivation”. Horizons of thermobaric decompression of rocks, which under the influence of stresses, multidirectional deformations, and vibrations, acquire the properties of strongly dislocated media forming extensive migration channels of fluids, “degassing pipes”.  They provide the movement of useful mineral media to the surface and the zones of intense relaxation of tectonic stresses, especially in the form of earthquakes. Practical significance. The results of the studies give an opportunity to clarify the geological and structural features of the structure of the Earth's crust of Transcarpathia, to adequately interpret the spatial distribution of geophysical fields and to decipher the features of local geodynamics and seismotectonic process, to clarify the level and nature of geo-ecological hazards, to more effectively predict and study deep regional distribution of mineral resources.

1. Alers, D. (1968). Using measurements of sound velocity for determining the Debye temperature in solid bodies. Dynamics of lattice. Moscow: Mir, рр. 13-61. (in Russian).
2. Burtnyi, P. A., Korchin, V. A., Karnaukhova, E. E. (2013). Modelling matter composition of the deep horizons of the Earth's crust (a new conception of the interpretation of geophysical data). LAP Lambert Academic Publishing House, Saarbrücken, Deutschland, 188 р. ISBN: 978-3-659-38626-8. (in Russian).
3. Chekunov, A. V., Livanova, L. P., Geyko, V. S. (1969). Deep structure and certain peculiarities of the tectonics of the Transcarpathian depression. Soviet Geology, 10, 57-68. (in Russian).
4. Chekunov, A. V., Sologub, N. V., Starostenko V. I. et. al. (1994). The deep structure and geodynamics of the Carpathians. Lithosphere of Central and Eastern Europe: Young Platforms and Alpine fold complex / ed. by Chekunov A.V. Naukova Dumka Publishin House, Kyiv., p. 121-174. (in Russian).
5. Christensen, N. (1989). Reflectivity and seismic properties of the deep continental crust. Journal of Geophysical Research, 94(17), 793-804.
6. Christensen, N., Mooney, W. (1995). Seismic velocity structure and composition of the continental crust: A global view. Journal of Geophysical Research, 100(B7). 9761-9788.
7. Geguzin, Y.E., Krivoglaz, M.A. (1971). Migration of macroscopic inclusions in solid bodies. Moscow: Metallurgia, 344 р. (in Russian).
8. Gordienko, V. V., Gordienko, I. V., Zavgorodnyaya, O. V., Kovachikova, S., Logvinov, I. M., Tarasov, V. N., Usenko, O. V. (2011). The Ukrainian Carpathians (geophysics, deep processes). Logos Publishing House, Kiev, 128 р. ISBN 978-966-171-350-4. (In Russian).
9. Gordienko, V. V., Gordienko, L.Ya. (2019). Asthenospheric lenses in the mantle of oil and gas regions. Geology of mineral resources and the World Ocean, 2, рр. 35-51. (In Russian). https: // 15407./gpimo2019.02.035
10. Kern, H. (1978). The effect of high temperature and high confining pressure on compression a wave velocity in quartz-bearing and quartzfree igneous and metamorphic rocks. Tectonophysics, 4, 185-203.
11. Korchin, V. A. (2013a) Thermodynamics of crustal low velocity zones (a new scientific hypothesis). LAP Lambert Academic Publishing, Saarbrücken, Deutschland, 280 р. (in Russian).
12. Korchin, V. A. (2013b). Crustal low velocity zones - perspective horizons for localization of deep hydrocarbons. Deep oil, 8, рр. 1099-1116. (in Russian).
13. Korchin, V. A. (2017). Anomalies of low density in the crystalline crust of thermobaric origin: a new insight into migration and localization of hydrocarbons. In: Gasi, S and Hachay, O (Eds) Oil and Gas Exploration: Methods and Application. Monograph Number 72. Wiley, рр. 237-257.
14. Korchin, V. A. (2018). Features of thermobaric elastic-density anomalies of the Еarth's crust of seismically-tectonically active regions. Modern problems of mechanics, 33(3), 244-254. ISSN 1694-6065. (in Russian).
15. Korchin, V. A., Burtnyi, P. A., Karnaukhova, E. E. (2018a). Decompaction of metamorphic rocks under thermodynamic conditions of the Earth's crust (experimental data). Geophysical Journal, 40(4), 107-130. DOI: 10.24028/gzh.0203-3100.v404.2018.140612. (in Russian).
16. Korchin, V. A., Burtnyi, P. A., Karnaukhova, E. E. (2018b). Thermobaric decompression zones of the crustal rocks are natural satellites of seismo-tectonically active regions. Modern problems of mechanics, 33(3), 399-409. ISSN 1694-6065. (in Russian).
17. Korchin, V. A., Burtnyi, P. A., Karnaukhova, E. E. (2019а). Transcarpathian petrophysical thermobaric model along the RP-17 seismic profile. Actual prospects for the development of geology: science and production: Materials of the VІ International Geological Forum (Odessa, Ukraine, June 17-22, 2019), Kiev: USGRI, рр. 116-119. ISBN 978-966-7896-85-0. (in Russian).
18. Korchin, V. A., Burtnyi, P. A., Karnaukhova, E. E. (2019b). The prognosis Transcarpathia petrophysical thermobaric model along the RP-17 profile. Geophysics and geodynamics: forecasting and monitoring of the geological medium / Edited by Maksimchuk V., Lviv: Rastr-7, рр. 68-70. ISBN 978-617-7726-70-7. (in Ukrainian).
19. Korchin, V. A., Burtnyi, P. A., Kobolev, V. P. (2013). Thermobaric petrophysical modelling in geophysics. Naukova Dumka Publishin House, Kiev. ISBN: 978-966-00-1360-5, 312 р. (in Russian).
20. Korchin V., Rusakov O. (2019). The regional thermobaric trap for mantle hydrocarbons in the crystalline crust of the Ukrainian NW Black Sea sector. 18th International Conference on Geoinformatics -Theoretical and Applied Aspects. 13-16 May 2019. Kyiv, Ukraine. DOI: 10.3997/2214-4609.201902054.
21. Kutas R. I. (1978). Field of heat flows and a theoretical model of the Earth's crust. Naukova Dumka Publishing House, Kiev, 140 р. (in Russian).
22. Kutas R. I. (2014). Heat flow and geothermal models for the Earth's crust of the Ukrainian Carpathians. Geophysical Journal, 36, 6, рр. 3-27. DOI: (in Russian).
23. Kutas R. I. (2016). Geothermal conditions and the Mesozoic-Cenozoic evolution of the Carpathian-Pannonian region. Geophysical Journal, 38, 5, рр. 75-107. DOI: 10.24028/gzh.0203-3100.v38i5.2016.107823. (in Russian).
24. Milanovsky, S. Yu., Nicolaevsky, V. N. (2009). The role of fracturing in the evolution of the Earth's crust. Tectonophysics and current issues of Earth sciences. Col. of Materials of reports of the All-Russian Conference. (8-12 October 2009, Moscow, Russia). Vol. 2. Moscow: IEP, p. 71-103. (in Russian).
25. Milanovsky, S. Yu., Nicolaevsky, V. N. (2010). Processes of transfer (migration) in the system of the Earth's crust. Modern methods of seismic survey in searching for oil and gas under conditions of complex structures (Seismo 2012), 16-22 September 2010, Kurortnoe, AR Crimea, Ukraine. The International scientific and practical conference, p. 37- 44. (in Russian).
26. Nashchekin, V. V. (1969). Technical thermodynamics and heat transfer. Moscow: Higher school, 560 р. (in Russian).
27. Nazarevich, A. V., Nazarevich, L. E. (2002). Deep trap-collector tectonic structures in the lithosphere of the Carpathian region of Ukraine: nature, origin and perspective resources. Scientific bulletin Ivano-Frankivsk National Technical University of Oil and Gas, 3 (4), 10-21. (in Ukrainian).
28. Nazarevich, L. E., Nazarevich, A. V. (2004). Technique of refining the parameters of the hypocenters of the Carpathian earthquakes. Geodynamics, 1 (4), 53-62. (in Ukrainian).
29. Nazarevich, L. E., Nazarevich, A. V., Kovalishin, Z. I. (2002). Nature of the lowered velocities subzone in «granites» of the Transcarpathian crust and its potential recourses. Visnuk of the Lviv University, Geology Series, 15, 119-125. (in Ukrainian).
30. Nazarevich, L.E., Nazarevich, A.V., Starodub, G.P., Nazarevich P. A. (2011). On multistage of the seismotectonic process in the Ukrainian Transcarpathia and its relationship to the crustal structure of the region and properties of its matter. Modern Tectonophysics. IPE RAS: Moscow, рр. 179-186. (in Russian).
31. Nikolaevsky, V. N. (1966). Geomechanics and fluid dynamics. Moscow: Nedra, 447 p. (in Russian).
32. Reider, E. (1987). Fluid inclusions in minerals. Moscow: Mir, 632 р. (in Russian).
33. Rusakov, O. M., Korchin, V. A. (2015). The origin and accumulation of abiogenic methane in the crystalline crust of the NW Black Sea shelf. Materials of the 4st Conference on Deep Origin of Oil "Kudriavtsev readings", Moscow, JSC CGE, CD- ROM. (in Russian).
34. Tretyak, K. P., Maksimchuk, V. Yu, Kutas, R. I. (Eds)., 2015. Modern geodynamics and geophysical fields of Carpathians and contiguous territories. Polytechnic Publishing House, Lviv, 420 р. ISBN 978-617-607-763-3 (in Russian).
35. Tripolsky, A. A., Sharov, N. V. (2004). The lithosphere of the Precambrian shields of the northern hemisphere derived from seismic data. Petrozavodsk: Karelian scientific centre RAS, 159 р. (in Russian).