Integrated geophysical and emplacement modelling of the Märjamaa and Kloostri rapakivi granitoids, Estonia: Insights into intrusion geometry and tectonic controls

The . 1.62 Ga buried Märjamaa and Kloostri rapakivi granitoids in western Estonia consist of three magmatic phases. This study utilizes processed Bouguer gravity and magnetic anomaly data to model the internal architecture and emplacement geometry of the granitic bodies, testing how inherited crustal structures influenced these processes within the context of the Mesoproterozoic Anorthosite–Mangerite–Charnockite–Granite (AMCG) magmatism in Fennoscandia. Potential-field data were processed through spectral separation and derivative filters (TDR, TDX, AS), complemented by lineament extraction and density mapping. A cross-gradient joint inversion using the SimPEG Python module, conducted down to 10 km, delineates three-dimensional density and susceptibility contrasts. Potential lineaments align with Riedel shear patterns along the NW-trending, dextral-oblique Åland–Paldiski–Pskov Deformation Zone (PPDZ), indicating transtensional pull-apart reactivation that focused magma ascent and suggesting that 1.6–1.4 Ga AMCG rapakivi granites and coeval basins formed through reactivation of Svecofennian fabrics. Phase I rooted deeply, formed as a steep-sided tabular granodiorite body that evolved into a piston–cauldron structure through roof collapse and block assimilation, producing positive magnetic and Bouguer anomalies. Phase II intruded as a surrounding granite ring during continued subsidence, associated with negative gravity anomalies. Phase III represents a latest age trachytic Kloostri leucogranite emplaced by asymmetric subsidence, characterized by positive magnetic and negative Bouguer signatures. The phases were placed during the final stages of the first Fennoscandian rapakivi AMCG event (i.e. Wiborg suite), driven by asthenospheric upwelling and mafic underplating from superswell activity, within Nuna’s breakup configuration. Overall, the results support a crustal structure-controlled emplacement in which shear-zone reactivation affect the geometry of the Fennoscandian rapakivi intrusions.