The origin of magnetic anomalies in lower crustal rocks, Labrador

Mid‐ to lower crustal granulites near Wilson Lake in Central Labrador exhibit pronounced aeromagnetic anomalies. Areas characterized by high and low field strength correlate with the Wilson Lake allochthon and the surrounding autochthon respectively. The induced magnetization in both units has mean values of 0.34 A/m (allochthon) and 0.33 A/m (autochthon). However, the mean values of remanent magnetizations are 9.2 A/m (allochthon) and 3.3 A/m (autochthon) in directions contributing to the present geomagnetic field. Therefore, the remanent magnetization plays the main role in generating the observed magnetic anomaly. Thermal demagnetizations indicate that titanhematite is stable to 585–600 °C. The absence of significant Verwey transitions indicates that titanhematite is the predominant carrier in some rocks and a significant carrier along with magnetite in others. Any interpretation of the magnetic anomalies above these rocks must consider magnetic remanence as the principle anomaly source.