Compressional tectonics related to Fuegian orogeny: Insights from AMS and structural geology in Navarino Island, Chile

Abstract

Navarino Island is located in the southernmost part of South America, within the Central Belt of the Fuegian Orogen. The shortening of the geological units observed on the island is believed to be related to a compressional event during the closure of the Rocas Verdes Basin. However, the full extent of this relationship remains unclear due to accessibility challenges and the apparent change in the stratigraphic records both north and south of the Beagle Channel. In this study, we integrate anisotropy of magnetic susceptibility (AMS) with structural observations across turbiditic sandstones and mudstones from the Lower Cretaceous Yahgan Formation. We analyzed thirty new sampling sites located along the northern coast of the island and the Dientes de Navarino mountain group. The AMS data exhibited predominantly oblate magnetic fabrics, with P’ values ranging from 1.02 to 2.22. The ellipsoid orientations correlated well with the structural features, particularly cleavage (S1) and fold axes. High P’ values and tectonic fabric types were concentrated in the western part of the island. A transition from a tectonic fabric with lower anisotropy degrees to a more sedimentary fabric was observed towards the east and south. These findings reflect a W-E deformation gradient consistent with the island´s structural features, including an overprinting cleavage family (S2) restricted to the island’s northwest. This study highlights the utility of AMS in elucidating strain directions and reconstructing deformation histories in complex orogenic settings.