Paleomagnetism of the Carboniferous Tepuel Group, central Patagonia, Argentina

Abstract

Samples of the Carboniferous glaciogenic sequences of the Tepuel Group, western central Patagonia, Argentina, were collected from 23 sites in two localities, Sierra de Tepuel (43.7°S, 70.5°W) and Las Salinas (43.2°S, 70.3°W). Most were fine sandstones to siltstones of late Visean to Westphalian age. A characteristic remanent magnetization was determined in most sites by alternating field and/or thermal cleaning. At Sierra de Tepuel all samples were partially overprinted by a secondary magnetization apparently related to Mesozoic magmatic activity in this area. However, site mean directions of the characteristic remanence from both localities passed a tilt test, indicating a pretectonic (pre‐Early Permian?) magnetization. Isothermal remanent magnetization experiments showed magnetite as the main and often the only magnetic carrier, while thin section analyses indicated a detrital origin for this mineral, suggesting a depositional or postdepositional magnetization. The paleomagnetic pole for the Tepuel Group (Namurian‐Westphalian) at 316.1°E, 31.7°S (number of sites N = 16, minor and major semi‐axes of confidence δp = 15.0°, δm = 16.0°), is considered a key pole for the Middle Carboniferous of South America and Gondwana, confirming the apparent polar wander path for the supercontinent for which the pole moved from central to southern Africa in the Early Carboniferous, followed by a rapid motion from southern Africa to Antarctica during the late Westphalian. The agreement of the Tepuel pole with this Gondwanan path confirms that Patagonia was already part of South America by the Middle Carboniferous.