The interplay of the thermal and structural histories of the Magura Nappe (Outer Carpathians) in Poland and Slovakia

X-ray diffraction studies of illite-smectite provide a tool for the reconstruction of the burial,thermal history and tectonic activity of the Magura Nappe in the Outer Carpathian arc. The observedthermal alteration of the rocks on the present-day erosion surface of the nappe reflects temperatures from< 75 to 200C associated with tectonic burial to depths between < 4 and 11 km.The present-day thermal structure of the Magura Nappe was largely established during the growth of anaccretionary wedge. An outwardly directed decrease in thermal alteration across the nappe as well asa positive correlation between the age of rocks and the grade of their alteration are both related to the growthof this wedge. The thermal alteration of the Magura Nappe was accomplished before emplacement into itspresent-day structural position.Two main stages of uplift and erosion can be identified. The first, which took place before Karpatiantimes, resulted in the removal of up to 4 km of strata. The second stage was related to the subsequentthrusting with co-eval internal deformation of the Magura Nappe over its foreland. The accretion-relatedthermal structure was greatly modified during this later event. Uplift was significantly influenced by themorphology of the Carpathian basement. The amount of erosion was greatest above and inward from thebasement slope and involved exhumation of the most altered rocks. This stage, initiated in the EarlyMiocene, was still in progress in Early Sarmatian times.