Crustal and Lithospheric Structure of the Carpathian–Pannonian Region— A Geophysical Perspective: Regional Geophysical Data on the Carpathian–Pannonian Lithosphere
L. Pospíšil, A. Ádám, J. Bimka, P. Bodlak, T. Bodoky, P. Dövényi, H. Granser, E. Hegedüs, I. Joó, A. Kendzera, L. Lenkey, M. Nemčok, K. Posgay, B. Pylypyshyn, J. Sedlák, W. D. Stanley, G. Starodub, V. Szalaiová, B. Šály, A. Šutora, G. Várga, T. Zsíros, 2006. "Crustal and Lithospheric Structure of the Carpathian–Pannonian Region— A Geophysical Perspective: Regional Geophysical Data on the Carpathian–Pannonian Lithosphere", The Carpathians and Their Foreland: Geology and Hydrocarbon Resources, Jan Golonka, Frank J. Picha
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Research of the lithosphere of the Western Carpathians, based on the analysis and interpretation of the complex geological and geophysical data, has brought several remarkable results that enable us to understand more precisely the development of the sedimentary basins. First, a tight relationship between gravity anomalies and sources originated from Tertiary sedimentary basins that creates substantial parts of the gravity effect. The main part of the gravity effects originating from both the Moho discontinuity and the boundary between lithosphere and asthenosphere is mutually compensated for in the region of the Carpathians, and therefore, it can be traced only with difficulties.
Copyright ©2006. The American Association of Petroleum Geologists.
In this chapter, basic information regarding the study of the gravity field of the Western Carpathians are presented, and these both describe the most significant anomalies and the features of the gravity field of basins and support the significance of gravity in the process of verification of interpretation of seismic, magnetotelluric, and geological models in the area of contact of the Inner and Outer Carpathians and the models of the lithosphere.
The fundamental results of deep seismic sounding in the Carpathian–Pannonian region constitute the next part of the presented data, especially the observation of the Moho reflection by deep seismic reflection surveys (in 1955), the deepening of the crust–mantle boundary under the surrounding mountain range inferred from international refraction and wide-angle reflection surveys (1964–1975), the detection of seismic reflection arrivals of several kilometers originating from the upper mantle and in quantifying the depth of the lithosphere–asthenosphere boundary by determining the velocity-vs.-depth function of the P waves (1975–1981), the determination of a domal uplift of the lithosphere—asthenosphere boundary, and the existence of shear zone systems cutting through a significant part of the lithosphere (1990–2000).
The seismicity of the Carpathian Basin is summarized based on a comprehensive earthquake catalog with more than 20,000 events. The recurrence curve of earthquakes predicts an earthquake of magnitude M 5 every 1 yr, an earthquake of magnitude M 6 every 10 yr, and an earthquake of magnitude M 7 every 100 yr in the Carpathian Basin on average. Most of the shallow-depth events originate from the 5–15-km (3–10-mi) depth domain, whereas in the Vrancea region, roughly three groups can be outlined with depth centers of about 15, 80, and 130 km (10, 50, and 80 mi), respectively. The average yearly energy release is 6.1 × 1013 J in the whole basin, and the contribution of the Vrancea zone to this amount is 4.8 × 1013 J/yr, whereas 1.3 × 1013 J/yr is the product of the remaining large part of the studied area.
The synthetic seismograms for the International Geotraverse II of the Eastern Carpathian lithosphere structure were calculated. Geology, seismic, heat, gravity, and electromagnetic data were considered. Vertical and horizontal variations of velocity, density, and energy dissipation were approximated by means of the finite-element method. Synthetic seismograms were compared with experimental ones registered by West Ukrainian Uszhorod, Kosiv, and Miszhirja seismic stations. Effects of change of the lithosphere structure characteristics in the Eastern Carpathian cross section were interpreted on the seismic patterns of waves spreading through the explored cross section.
The most important part of the chapter compiles the data on the distribution of the electrical conductivity anomalies, which have been determined by magnetotellurics in the Earth’s crust and upper mantle in the Carpathian–Pannonian Basin. Among them, the Carpathian conductivity anomalies, the Transdanubian upper crustal conductor, the middle to lower crustal conducting layer, and the updoming asthenosphere are discussed in detail.
The interpreted resistivity model along the reflection profile 2T, which crossed the whole part of Western Carpathians in 1987–1988, has brought several surprising results that, in combination with reflection seismic, gravity, and other geophysical data, enable us to construct a more precise model of the Western Carpathian lithosphere.
The complex set of basic information supplies heat flow, recent vertical movement, and paleomagnetic data.
A new heat-flow map is presented for the Pannonian Basin, the Carpathians, and the surrounding region. A brief review summarizes the geodynamic and geothermal background of heat-flow pattern.
The investigation on recent vertical crustal movements in the Carpathian region offers very important information. As a first presentation, a new color map of vertical movements is enclosed, with 1-mm/yr isoline interval (see below section on The Recent Vertical Movements in the Carpathian Region). In the investigation, repeated precise geodetic measurements and oceanographic data have been used. The characteristic data of the movement tendencies, including the reliabilities of measurements and adjustment, have also been presented.
The most important paleomagnetic data are compiled and briefly discussed in this chapter. All these data suggest that the ALCAPA terrane rotated consistently counterclockwise but by different amounts, which indicates internal deformation of early to middle Miocene age. The Tisza unit underwent opposite rotation with respect to the northern unit. In conclusion, the rotation of the ALCAPA and Tisza–Dacia units with different sense occurred at a similar time between 19 and 15 Ma.