Multi-stage tectonic evolution of the Tatra Mts recorded in the para- and ferromagnetic fabrics

Abstract

The Tatra Mts form the highest part of the Carpathian mountain chain; however, their tectonic and thermal evolution is still debatable. Previous magnetic fabric studies have primarily focused on the crystalline basement and its autochthonous cover. We investigate the magnetic fabrics of Cretaceous marly limestones from a Mesozoic nappe unit and post-thrusting Oligocene shales and mudstones to unravel the most recent tectonic evolution of the Tatra massif. In addition to standard petromagnetic measurements such as the acquisition of the Isothermal Remanent Magnetization or temperature-dependent susceptibility analyses, we investigated the paleotemperature of the Tatra region because high temperatures are known to significantly affect the magnetic mineralogy. The most common minerals in the studied units are paramagnetic phyllosilicates which govern the in-phase Anisotropy of Magnetic Susceptibility. The ferromagnetic fraction is represented by fine-grained magnetite with a minor contribution of hematite. Measured and counted vitrinite reflectances document an eastward increase in maturity, which is also reflected in the magnetite–hematite grain size ratios. Because the paleotemperatures recorded in the Cretaceous rocks follow the same increasing trend as the post-thrusting shales, it appears that both units were affected by a single major thermal event linked presumably to the Late Oligocene/Early Miocene burial. We propose that magnetic fabrics carried by phyllosilicates document the impact of crucial tectonic phases such as Miocene uplift and Cretaceous thrusting, whereas the out-of-phase Anisotropy of Magnetic Susceptibility and Anisotropy of Anhysteretic Remanent Magnetization fabrics most likely record the stress orientation during major burial episodes. Finally, the conspicuous vertical ferromagnetic lineation present in some Cretaceous sites documents the transpression-controlled tectonic regime in the Oligocene–Early Miocene.