3D density modelling of Central Europe by an interdisciplinary interpretation of the CELEBRATION 2000 seismic experiments.
Final Report Abstract
The integrated geophysical-petrological 3D modelling using LitMod 3D has been performed in order to improve the existing 3D gravity model of Central Europe developed in the first part of the project. The improvements foreseen to be achieved in the second part of the project were related to two major tasks. Firstly, the structure of the upper mantle (including the depth to the lithosphere-asthenosphere boundary) had to be enhanced, since it influences to a great extent the crustal structure. Therefore, the most important task was to combine the crustal models from CELEBRAT1ON2000, SUDETES 2003 and ALPS2002 seismic experiments with lithospheric studies performed in the recent years in Central Europe. The petrological modelling served then as a tool to obtain a robust and relatively detailed large-scale model of Central Europe, which is based on the most recent geophysical data and petrological information. Secondly, the transition zones between the very different tectonic units of the Carpathian-Pannonian system and its surroundings were also targeted by the detailed integrated modelling. LitMod3D has been developed to perform integrated geophysical-petrological LIThospheric MODelling in a 3-D setting. It combines, in a self-consistent manner, concepts and data from thermodynamics, mineral physics, geochemistry, petrology, and solid-Earth geophysics. A model in LitMod3D is deflned by a number of mantle and crustal layers. Each of these layers is characterized by a set of input parameters (i.e. thermal conductivity, radiogenic heat production, pressure coefficient, major element composition of the mantle layers). In the crust, the density values of the layers are input parameters assigned by the user if possible they are constrained by seismic velocities, geological data and other additional data available. It is also possible to include vertical variations of the density within one layer the density gradient is either depth- or pressure-dependent The bulk properties of the mantle are computed applying different averaging schemes to the mineral phase properties. Hence, the mantle densities are calculated based on the in-situ conditions and are P/T dependent. The phase transitions (i.e. plagioclasespinel and spinel-garnet) are considered as well. This is a very important advantage, since ignoring the mantle phase transitions can significanfiy bias the gravity modelling of the shallow crustal structures. Thus, the upper-mantle densifies are thoroughly determined even in tectonic settings, where pronounced undulations of the lithosphere-asthenosphere boundary (LAB) are assumed (e.g. Pannonian Basin). Once the density and temperature distributions are known, LitModSD computes a number of geophysical observables: surface heat flow, elevation, geoid, Bouguer and Free Air gravity anomalies. These calculated values are compared to the measured data in order to construct a model (i.e. forward modelling technique). Modelling of several geophysical datasets simultaneously is a very powerful approach, which significanfiy reduces the uncertainties related to the modelling of these datasets separately. Therefore, this technique together with the results of numerous seismic experiments revealing structures of the lithosphere in Central Europe in various scales have enabled to develop a robust and self-consistent 3D model. The structure of the crust was taken and simplified from the results of 3D gravity-seismic modelling constrained by the above-mentioned seismic experiments. In addition, the most recent data constraining the depth to the LAB published were used. The results of the 3D Integrated modelling clearly indicate presence of several quite different mantle domains within the region modelled. While the Pannonian Basin has a thin and fertile lithospheric mantel, the mantel of the EEC is quite thick and includes an upper layer of depleted mantel material. The high-density uppermost manfie of - 8.4 km/s detected along some of the CELEBRATION 2000 seismic profiles is based on our integrated approach composed by very high-density (i.e. eclogitic) material. Our model includes also vertical sublithospheric anomaly underneath the Eastern Alps at depths 150-350 km imaged by Brückl et al. (2011) and interpreted as a subducted oceanic slab. In our model it was modelled as both temperature and compositional anomaly, thus cold body of oceanic composition. Such bodies have a significant effect on the potential field data due to the thermal and density variations they cause in the mantel. The minimal depth to the LAB has been modelled underneath the Pannonian Basin and reaches 72-100 km. Slightly deeper LAB of - 110 km is located underneath the European Platform north of the Bohemian Massif. The Bohemian Massif itself is characterized by LAB at depths of 120-140 km and similar values were modelled underneath the Carpathian Mountain chain. However, the Western Carpathians seem to have thinner lithosphere (120-130 km) than the Eastern Carpathians, where the LAB reaches depths of more than 130 km. Note that our model includes only the northernmost part of the Eastern Carpathians. The thickest lithosphere is present below the EEC, where the LAB has been imaged and modelled at depths > 200 km.
Publications
- Gravity and seismic modelling in the Carpathian-Pannonian Region. In: Vozar.J., Ebner, F., Vozarova, A., Haas, J., Kovács, S., Sudar, M., Bielik, M., Pero, C. (eds), Variscan and Alpine terranes of the Circum-Pannonian region. Slovak Acad. of Sc SAS., Geological Institue, Bratislava (2010): 202-233. ISBN 978-80-971609-9-9 (für 2. Aufl. 2014)
Bielik, M., Alasonati Tasarova, Z., Vozar, J., Zeyen, M., Gutterch, A., Grad, M., Janik, T., Wybraniec, S., Götze, H.-J., Grinc, M., Dererova
- Lithospheric structure of Central Europe: Puzzle pieces from Pannonian Basin to Trans‐European Suture Zone resolved by geophysical‐petrological modeling. Tectonics, Vol 35 Issue 3, March 2016, Pages 722-753
Alasonati Tasarova, Z., Fullea, J.C., Sroda, P., Bielik, M.,
(See online at https://doi.org/10.1002/2015TC003935)
