Paleomagnetism of the Clay-Howells Carbonatite Complex: Constraints on proterozoic motion in the Kapuskasing Structural Zone, Superior Province, Canada

The Clay-Howells Complex is located approximately 130 km east of Hearst, Ontario, at 49°50'N, 82°05'W near the north end of the Kapuskasing Structural Zone (KSZ) of the Superior Province in the Canadian Shield. The pluton is a large oviform pluton of about 16 km ² that is composed dominantly of syenite with minor Carbonatite. It was emplaced into an Archean gneissic terrain of amphibolite to granulite facies with Middle Precambrian diabase dikes. The complex is unmetamorphosed and Late Precambrian in age (Rb/Sr 1075 ± 15 Ma). Multistep alternating field (AF) and thermal demagnetization was carried out on 194 specimens from 18 sites in the intrusion and three sites in the host rock dikes and gneisses. The 18 syenite sites give a unit mean direction of 294.2°, 27.1° ( N = 18, k = 26, α ₉₅ = 7.0° ) which yields a pole position of 178.8° E, 26.5°N ( δ _p = 4.1° , δ _m = 7.6° ) for the Clay-Howells Complex. A crude contact test using the three host rock sites proved inconclusive. The pole for the intrusion is concordant, falling at about 1080 ± 10 Ma on the Keweenawan apparent polar wander path which agrees with the Rb/Sr age. Thus the complex has an untilted, primary remanence that indicates that there has been no significant uplift (< 10 km) or rotation (< 7°) on the KSZ since intrusion and therefore that all significant geotectonic activity on the KSZ must predate 1.1 Ga.