A new tectonic model for the Palaeoproterozoic Kautokeino Greenstone Belt, northern Norway, based on high-resolution airborne magnetic data and field structural analysis and implications for mineral potential

Abstract

The Palaeoproterozoic Kautokeino Greenstone Belt (KkGB) is a highly tectonised metasupracrustal belt sandwiched between the gneissic Ráiseatnu Complex to the west and the metaplutonic Jergul Complex to the east. The KkGB has been interpreted as an Early Proterozoic rift basin inverted during the Svecofennian orogeny (c. 1.9-1.7 Ga). The structural framework and tectonic development of the KkGB remain poorly investigated and understood. New airborne magnetic and structural data help to unravel the belt´s architecture and tectonic evolution, allowing its subdivision into two tectonic compartments. The eastern part shows NE-SW-trending, weak magnetic anomalies. The western part has pronounced NNW-SSE-trending anomalies. In the Jergul Complex, to the east of the KkGB, only relatively weak but pervasive NE-SW-trending anomalies are observed, similar to those in the eastern KkGB. These are locally deflected into NNE-SSW sets of discrete anomalies with a dextral offset. These two anomaly sets in the east are truncated by a pervasive set of NNW-SSE-trending strong anomalies in the western KkGB. The Jergul and Ráiseatnu Complexes display different aeromagnetic signatures suggesting that they are different terranes juxtaposed along the KkGB. Field structural analysis supports our interpretation of the geophysics. The eastern NE-SW-trending KkGB and the Jergul Complex contain flat-lying, west-dipping, NE-SW-trending shear zones accommodating dip-slip, top-to-the-east thrusting. The western NNW-SSE-trending KkGB is characterised by steeply dipping shear zones with both dip-slip and strike-slip kinematics. Strike-slip shear zones are predominantly sinistral, but coexisting sinistral and dextral kinematics are commonly observed together with steeply plunging lineations suggesting a degree of horizontal flattening. The NNW-SSE-trending shear zones, corresponding to the NNW-SSE-trending magnetic anomalies, form a mega-sinistral array truncating and sinistrally deflecting the earlier thrust structures. The KkGB is geometrically and kinematically similar to other Archaean-Palaeoproterozoic basement domains in northern Norway. Gold mineralisation at the Bidjovagge mine is genetically related to deformation along the NNW-SSE-trending ductile shear zone of the western KkGB.