3-D Inversion of MT Data for Imaging Deformation Fronts in NW Poland

Katarzyna Ślęzak,Waldemar Jóźwiak,Heinrich Brasse,Krzysztof Nowożyński

doi:10.1007/s00024-016-1275-2

Abstract

The Pomerania region (northwest part of Poland) occupies a significant position, where the largest European tectonic boundary is situated. This is the area of the contact between the East European Craton (EEC) and the Paleozoic Platform (PP) and it is known as the Trans-European Suture Zone (TESZ). The TESZ was formed during Paleozoic time as a consequence of the collision of several crustal units and it extends from the Black Sea in the southeast to the British Isles in the northwest. It is a region of key importance for our understanding of the tectonic history of Europe. Previous magnetotelluric (MT) results, based on 2-D inverse modeling, show that the contact zone is of lithospheric discontinuity character and there are distinct differences in geoelectric structures between the Precambrian EEC, transitional zone (TESZ), and the younger PP. The presence of a significant conductor at mid and lower crustal depths was also shown. Thus, the main aim of the research presented here was to obtain detailed, 3-D images of electrical conductivity in the crust and upper mantle and its regional distribution below the TESZ in the northwest part of Poland. To accomplish this task we applied the latest 3-D inversion codes, which allowed us to get more realistic model geometries. Additionally, to confirm and complement the study, the Horizontal Magnetic Tensor (HMT) analysis was realized. This method gives us an opportunity to efficiently locate the position of well-conducting structures. As a result we obtain a clearer, three-dimensional model of conductivity distribution, where highly conductive rock complexes appear which we tentatively connected to deformation fronts.

Highlights

Introduction and Geological BackgroundIn the Cambrian, the microcontinent Avalonia broke off from Gondwana and at the end of the Ordovician it collided with the Baltica continent
The WSW–ENE striking conductive complex (B) and related with it slightly more resistive structures (Figs. 7, 8b) one can see at a depth of 10–30 km (B). They are extending towards the west and located in a position of the Variscan Deformation Front (VDF) which is postulated by geologists (NARKIEWICZ and DADLEZ 2008)
The investigation area is located in the Trans-European Suture Zone (TESZ), the most pronounced geologic zone in Europe north of the Alpine

Summary

Introduction

In the Cambrian, the microcontinent Avalonia broke off from Gondwana and at the end of the Ordovician it collided with the Baltica continent. Afterwards, the combined Baltica and Avalonia collided progressively with Laurentia forming the Laurussia continent. This collision caused a mountain building era named the Caledonian orogeny. The Permo-Carboniferous collision of the continents Gondwana, Laurussia, and Baltica, termed the Variscan orogeny, molded the late Paleozoic supercontinent of Pangaea. The placement and mutual positions of Variscan Deformation Fronts (VDF) and Caledonian Deformation Fronts (CDF) are still a subject of discussion.

Methods

Results

Conclusion