Integrated modelling based on shallow cross-gradient joint inversion and deep petrological approach on 2D/3D data in the Western Carpathians

Abstract

<p>We present the integrated geophysical modelling based on magnetotelluric (MT) method included in the crustal joint inversion with gravity data performed by JIF3D code and geophysical-petrological LitMod3D thermaly-selfconsistent mantle modelling. Performed geophysical modeling is primarily based on MT and regional gravity data with supporting information from seismic methods and geothermal data like Moho and lithospheric-asthenospheric boundary (LAB) depth used for building of the starting models. The integration among geophysical models is provided by the cross-gradient coupling method for the crustal structures and in the mantle, the coupling is provided petrological relationship based on compositional, temperature and pressure distribution information. The case study is focused on 3D modelling of the seismic 2T profile in central Slovakia crossing the major Carpathian tectonic units and the contact zone between European platform and Inner Carpathian block, which coincide with Carpathian Conductivity Anomaly (CCA).</p><p>The geoelectrical models from the 3D integrated modeling image the CCA in depths of about 10 - 20km and shows great improvement in comparison with 2D MT models. The CCA exhibits 3D features represented by the offset, along the fault, in the northsouth direction in the northern part of the modelled area. The four basic segments were identified in the crust structure of the central Slovakia part of the Western Carpathians. The southernmost physically distinctive segment with high full crust conductivity caused by young volcanic activity shows the presence of the partial melt, with high geoelectrical conductivity, in the middle and lower crust caused by higher heat flow. These structures are situated to the southwest from the profile and finger type conductors indicate its penetration in northeast direction. These volcanic processes in the south are not connected with CCA presence and its origin, which is supposed to be the presence of graphite or mineralized water in mylonitized rocks on the sheer contact zones of European platform and Inner Western Carpathians.</p><p>For mantle part of the integrated models, we studied different mantle compositions and fluid content within the lithospheric mantle to explain differences in electrical and seismic LAB. The calculated petrological conductivity model shows sensitivity of MT data on the LAB depth change, the correct input of composition parameters of lithospheric mantle and thermal field. The thermal steady state approximation was used to calculate surface heat flow in the area is lower than measured and estimated values from previous thermal studies. The differences between calculated and measured heat flow is primarily caused by high radiogenic production within the crust and not by the contribution from mantle.</p>