Depth-to-basement study for the western Polish Outer Carpathians from three-dimensional joint inversion of gravity and magnetic data

Results of a depth-to-basement study are presented for the westernmost Polish Outer Carpathians. The gravity data are inverted for the top of the Precambrian basement using horizons from 2-D gravity and magnetic forward models and well tops as input depth measurements. 2-D models, used in the study, are built upon depth converted seismic profiles. The results are visualized as an isobath map for the top of the Precambrian basement, complemented with the qualitative structural interpretation of gravity and magnetic anomaly maps. The outcome of 3-D joint inversion of the gravity data and depth measurements shows the Precambrian crystalline basement deepening southward from c. 1 to almost 7 km b. s. l. Consequently, an approximately 2 km thick wedge of autochthonous sediments, thickening southward, is embraced between the crystalline basement and a sole detachment of the Carpathian fold-and-thrust belt, imaged by seismic data. Since the modelled top of the crystalline basement is roughly parallel to the Moho, suggesting no extension-related thinning in Mesozoic, the autochthonous sediments are likely of pre-Permian age. A positive magnetic anomaly in the south of the study area is presumably associated with the presence of an elongated body of intermediate to mafic rocks in the basement of the Brunovistulian Terrane. These rocks may represent a relic of a Cadomian magmatic arc comparable to that existing in the Brno Massif of southern Moravia.