Numerical modelling and mapping of Miocene dyke opening in the Cserhát Hills, Hungary
B.Sc. Dorina Juhász
The Cserhát Hills are located in mid-North Hungary, at the northern edge of the Pannonian Basin and are parts of the Miocene Inner Carpathian volcanic arc. The Cserhát Hills were strongly influenced by the Miocene volcanism and are built up by polycentric domes, stratovolcanoes, and radial a dyke-system, consistent with their location in an extinct volcanic arc. In the following research we are focusing on this radial dyke-system, which is often segmented and showing changes in their strike-direction. The main strike directions are E-W and N-S, but the dykes with different striking orientation may belong to different volcanic systems and have different ages, respectively. The thickness of the dykes varies between 3 m and 25 m, and the length of the segments varies between 1 km and 5 km. Partial re-mapping of the area was carried out. For studying the stress-field in the area of diking and its evolution, we carry out FEM (finite element method) numerical model of dyke opening by using COMSOL Multiphysics. For mapping the dykes some geophysical methods were tried as well, including multielectrode method and RMT (radio magnetotelluric) measurements.
The extensional structures, which were measured in the bedrock, agree with the stress-fields of previous studies. To expand the previous datasets of the stress field, the cooling joints of the dykes were measured as well. Two sets of cooling joints were identified in the field, one with strike parallel to the dyke, which probably developed during the propagation, and the second is perpendicular to the dyke, which might be the consequences of the dyke intrusion. These data gave a base for the modeling. The aim is to compare numerical models with field observations to shed light on the local and tectonic stress fields, and pressure conditions in the magmatic systems involved. The numerical models provide insight on how large stress was needed to open Cserhát Hills dykes, and if the previous strain field in the area had an influence in this.