Abstract

Ragged Pluton is a member of the Tungsten Plutonic Suite in the eastern Selwyn Basin. This circular massive 97 Ma granitic pluton is ∼5 km in diameter. It intrudes deformed and metamorphosed clastic strata of the Neoproterozoic to Lower Cambrian Vampire Formation. Thermal and alternating field step demagnetization data for 216 specimens from 21 plutonic sites isolated a stable characteristic remanent magnetization (ChRM) direction at 20 sites of declination D = 325.9°, inclination I = 80.4° (α95 = 2.7°, k = 142). Thermal demagnetization and saturation remanence analysis show that the ChRM is carried by both single-domain pyrrhotite and magnetite. Ragged Pluton’s paleopole at 73.9°N latitude, 191.4°E longitude (dp = 5.0°, dm = 5.2°) is concordant with its co-eval 97 Ma North American reference paleopole, showing at 95% confidence that the pluton has not been significantly rotated or translated relative to North America. This paleomagnetic result favours tectonic models in which the eastern Selwyn Basin is autochthonous, or nearly so, since the mid Cretaceous.

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