3D magnetotelluric modelling of the Alnö alkaline and carbonatite ring complex, central Sweden

• Thirty-four broadband magnetotelluric stations were deployed across the Alno alkaline and carbonatite ring intrusion in central Sweden. The measurements were designed such that both 2D models along existing seismic profiles and a 3D model can be constructed. Alno Island and surrounding areas are densely populated and industrialized and in order to reduce the effect of noise, the remote reference technique was utilized in time series processing. Strike and dimensionality analyses together with the induction arrows show that there is no homogeneous regional strike direction in this area. Therefore, only the determinant of the impedance tensor was used for 2D inversion whereas all elements of the impedance tensor were used for 3D inversion. Representative rock samples were collected from existing outcrops and their resistivities were measured in the laboratory to facilitate interpretation of the inversion models. The results from these measurements show that coarse grained (sovite, white color) and fine-grained (dark color) carbonatites are the most conductive and resistive rock types, respectively. In accordance with the interpretation of the reflection seismic images, the 2D and 3D resistivity models depict the caldera-related ring-type fault system and updoming faulted and fractured systems as major 10-500 Omega m conductors, extending down to about 3 km depth. A central similar to 4000 Omega m resistive unit at about 3 km depth appears to correspond to a solidified fossil magma chamber as speculated from the reflection seismic data and earlier field geological studies.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geofysik (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geophysics (hsv//eng)

Nyckelord

Alnö; Carbonatite; Alkaline; 3D; Magnetotelluric; Resistivity

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)