Magnetic crustal structures in northern Fennoscandia

Abstract

Cooperation between the Nordic countries has produced a set of geophysical and geological maps in the region north of the 66th parallel in northernmost Europe. The area covers the transition from oceanic crust to the Baltic Shield, a section of the Caledonides, and a part of the Arctic platform. An interpretation of the aeromagnetic and gravity maps reveals several large structural units with distinct boundaries and characteristic anomaly patterns. In combination with data on rock physical properties, some general magnetic crustal features can be outlined: 1. (1) typical occurrence of magnetically banded ocean crust anomalies, 2. (2) the occurrence of magnetically banded patterns in the continental crust connected with metasupracrustal formations separated by culminations of high-density and high-magnetization basement domes and megashear zones (thrusts and transcurrent faults) with large displacements, 3. (3) occurrence of magnetic granitoid batholiths, 4. (4) general low remanence of shield rocks, allowing straightforward interpretation of magnetic total field anomalies, and 5. (5) general low magnetization of Caledonian thrusted units allowing mapping of the depth to their magnetic basement. Merging magnetic, gravity and petrophysical data allows constraints to be applied when modelling crustal structures. Some of the large-scale structural features are illustrated and some examples of profiles through the upper crustal structures are shown.