Paleomagnetic Constraints From South Georgia on the Tectonic Reconstruction of the Early Cretaceous Rocas Verdes Marginal Basin System of Southernmost South America

Abstract

South Georgia exists as a microcontinent along the North Scotia Ridge ∼1,700 km east of Cape Horn. The tectonostratigraphic units of South Georgia have long been correlated with those of the Fuegian Andes of southernmost South America. Accordingly, South Georgia has been regarded as a continuation of the Late Jurassic–Early Cretaceous Rocas Verdes marginal basin system, formerly situated south of Burdwood Bank and east of Cape Horn. To test this, paleomagnetic analysis of samples from the Larsen Harbour Complex, Drygalski Fjord Complex, and Annenkov Island Formation of South Georgia showed that 21 sites yield a mean direction of D = 328.5°, I = −62.1° (a95 = 3.5°) and a paleomagnetic pole at 068.2°E, 67.2°N, A95 = 4.7°. The consistency of directions and strong polarity bias, plus indications of a negative differential tilt test, point to a secondary magnetization acquired in the Late Cretaceous. Comparison of predicted versus observed directions for South Georgia relative to stable South America indicate 27.2 ± 11.2° of counter‐clockwise rotation (and 10.5° ± 4.5° of northward tilting) since the acquisition of magnetization. These results are consistent with paleomagnetic studies from the Fuegian Andes and support a paleoposition of the South Georgia microcontinent south of Burdwood Bank as strongly indicated by the geologic evidence. Partitioning this rotation between oroclinal bending during the Rocas Verdes basin collapse in the Late Cretaceous and left‐lateral translation along the North Scotia Ridge is not possible on paleomagnetic grounds, but the co‐linearity of Andean structures between the restored microcontinent and Tierra del Fuego indicates the former.

Cretaceous Crust in the Scotia Sea: Missing Pieces in a Geological Puzzle?

“…In our reconstruction (Figure 5c) the area in between the northern West Scotia Ridge and the East Scotia Ridge experiences extension, which results in stretching in the Central Scotia Sea domain and in South Georgia separating with a 90°counterclockwise rotation, away from the Central Scotia Sea, which is more than the 30°c ounterclockwise rotation that has been reported (Beaver et al, 2022). In our model, this results in an app.…”

Plate Rotation of the Northern Antarctic Peninsula Since the Late Cretaceous: Implications for the Tectonic Evolution of the Scotia Sea Region

“…Dredged in situ arc basalts from the margin of the South Orkney microcontinent and Powell Basin have been dated at about ∼85–68, 49–47, and 4.5–0.1 Ma by K/Ar method, along with a northeastward migration (Barber et al., 1991). Paleomagnetism, geochemical composition of dredged rocks, and provenance analysis show that the banks and microcontinents of the North and South Scotia Ridges were separated from southern Patagonia and northern Antarctic Peninsula, respectively (Beaver et al., 2022; Carter et al., 2014; Dalziel et al., 2021; Eagles, 2016; Pandey et al., 2010; Riley et al., 2019).…”