Paleomagnetism of the 1.1 Ga Lackner Lake Complex and tectonics of the Kapuskasing Structural Zone

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Abstract
The Middle Proterozoic Lackner Lake Complex is a circular alkalic syenite–carbonatite stock with a diameter of about 5.5 km. It intrudes granulite-rank Archean gneisses in the Kapuskasing Structural Zone of the Wawa Subprovince in the Superior Province of the Canadian Shield. It adjoins the Ivanhoe Lake fault zone, which forms the boundary with the Abitibi Subprovince and is the probable locus of maximum motion between the subprovinces. Specimens from 18 sites in the complex were analyzed paleomagnetically by alternating-field and thermal demagnetization and by saturation isothermal remanence tests. Large, recent viscous remanence components required removal before a stable remanence with a mean direction of 305.4°, 64.1 °(α95 = 5.2°) was isolated. Its pole of 53.7°N, 156.5°W (dp = 6.7°, dm = 8.3°) indicates emplacement at 1108 ± 10 Ma during a brief normal interval in a predominantly reversed-polarity time. This study indicates that there has been no postintrusion tilting of the Kapuskasing Structural Zone and that postintrusion uplift by unroofing did not exceed about 8 km.

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