Multiple episodes of dike emplacement along the northwestern margin of the Superior Province, Manitoba

Abstract

Three stable magnetization components A, B, and C have been isolated from a set of dikes that have been collectively referred to as the Molson swarm. Positive baked contact tests and square‐shouldered thermal decay curves indicate that these components were acquired during three periods of dike emplacement. Dikes carrying A with a pole at 15.4°N and 96.5°W (A 95 = 4.1°, N = 16 sites) have been dated by the U‐Pb method at 1883 Ma and are closely related to the Paleoproterozoic Trans‐Hudson Orogen. Ages of B with a pole at 27.1°N and 140.8°W (A 95 = 3.8°, A 95 = 3.0°, N = 30) and C with a pole at 40.7°N and 156.3°W (A 95 = 9.7°, N = 19) are estimated at 2170–2120 Ma, on the basis of paleomagnetic characteristics that are distinct from the A component, the analysis of metamorphic history of the Pikwitonei Domain, and comparison with well‐dated paleomagnetic poles from mafic igneous rocks in the Superior Province. The associated B and C dikes were emplaced in normal and reversed geomagnetic fields when the northwestern margin of the Superior Province experienced initial rifting prior to the Trans‐Hudson Orogen. These earlier dikes may correlate with known 2094 Ma mafic magmatism documented in the lower Hurwitz Group of the Hearne Province. A stable magnetization component D with a pole at 20.9°N and 133.6°W (A 95 = 7.6°, N = 30 samples) was also identified from unbaked granulites throughout the Pikwitonei Domain. This component predates all dike intrusion in the region, has an age range of 2200–2170 Ma, and may have been caused by earlier uplift of the northwestern Superior Province.