Seismic imaging of lower Carboniferous volcanic intrusions along the SW edge of the East European Craton in Poland

Until recently, early Carboniferous volcanic activity along the SW edge of the East European Craton (EEC) in Poland has been documented only by wells and, to some degree, by magnetic data. Recently, regional PolandSPAN seismic reflection survey, acquired by ION Geophysical above the entire cratonic edge in Poland, provided unique subsurface insight into this very important event of an extensive volcanic activity. This onshore seismic survey was acquired with ultra-long offsets (12 kms), tight station spacing (25 m), high fold (480) and was processed up to PSDM. 12 seconds record lengths of uncorrelated data provided imaging down to 60 km, with superior data resolution for the entire Phanerozoic sedimentary cover.

In N Poland, within the Mazury High, where Palaeozoic sedimentary cover has been eroded prior to the Permo-Mesozoic deposition within the marginal part of the Polish Basin, the Tajno pyroxenite-syenite-carbonatite complex, the Ełk syenite massif, the Pisz gabbro-syenite massif and Mława syenite massif, all of early Carboniferous age, have been drilled by numerous wells. In the Baltic Basin, where the Ediacaran – Silurian sedimentary cover has been preserved, numerous wells documented doleritic sills of the same age. In this area, a complex system of strong amplitude seismic reflectors of length reaching up to 100 km has been detected using PolandSPAN seismic data. These seismic features are located within the crystalline basement of the Baltic Basin at depth of 7-14 km, and closely resemble lower-crustal reflections (LCR) documented e.g. within the basement of the North Sea basin.

Another type of seismic features related to the lower Carboniferous volcanic intrusives has been documented in SE Poland within the Lublin Basin, where EEC crystalline basement is overlain by thick Ediacaran – Paleozoic – Mesozoic sedimentary cover. In this area, numerous wells encountered lower Carboniferous doleritic intrusions hosted by the Upper Devonian carbonates, and lower Carboniferous basaltic effusives. PolandSPAN data from the Lublin Basin revealed numerous saucer-shaped, strong amplitude seismic reflectors, characterized by lobate morphology and located at depths of 4-7 km, within the topmost Silurian–Lower Devonian section. Collectively, they form ca. 70 km long network of seismic reflectors. They were interpreted as saucer-shaped igneous sills, similar to igneous intrusions imaged by seismic data in other sedimentary basins. Some of these sills have been incorporated into the late Carboniferous compressional deformations of the frontal Variscan fold and thrust belt.

This study was supported by NCN grant UMO-2021/41/B/ST10/03550.