Internal structure of the buried Suwałki Anorthosite Massif (East European Craton, NE Poland) based on borehole, magnetic and gravity data combined with new petrological results

Abstract

Advanced magnetic and gravity data analysis has been used to acquire geophysical constraints providing new insights into the geological structure of the Suwałki Anorthosite Massif (SAM). The large negative magnetic anomaly of the SAM anorthosite intrusion is a result of the negative inclination of remanent magnetization, directed antiparallel to the present Earth’s magnetic field. Several filtering processes were applied to the magnetic and gravity maps to better understand the subsurface geology of the SAM area. The geological analysis of residual magnetic and gravity anomaly maps reveals the presence of different rock units, reflecting variation in petrological composition of the crystalline basement rocks. The 2-D modelling of magnetic and gravity data delineate the location and extent of the anorthosite-norite massif. The data is consistent with a thick upper crustal body with density 2690 kg/m3, low susceptibility (0.005 SI) and natural remanent magnetization (1.95 A/m), having inclination of I = –68°, and declination of D = –177°. The rocks bordering the central anorthosite body consist of norite and gabbronorite, granodiorite, diorite and charnockite. These main crystalline basement crustal units are shown more precisely on a new geological map of the SAM.