Deformation along the Deseado Massif (Patagonia, Argentina) during the Jurassic Period and its relationship with the Gondwana breakup: paleomagnetic and geochronological constraints

Abstract

This work presents the analysis of paleomagnetic results obtained from four sampling areas of the Jurassic Bahía Laura Complex in the Deseado Massif and their implications on the regional deformation history during the breakup of Gondwana. Paleomagnetic data show cessation of tectonic block rotations about vertical axes around 160 Ma and a change from a transtensional to a mainly extensional tectonic regime. Two biotite samples yielded 40Ar––39Ar radiometric ages: one from the eastern outcrops of the Chon Aike Formation (plateau age of 184.66 ± 0.55 Ma) and the other from the La Matilde Formation (plateau age of 157.40 ± 0.65 Ma), located at the central part of the Deseado Massif. Finally, an apparent polar wander path (APWP) was calculated for the Jurassic of South America (200 to 140 Ma). This APWP indicates that South America experienced a northward drift between 200 Ma and 170 Ma, a clockwise rotation (~10°) between 170 Ma and 160 Ma, and a westward drift between 160 Ma and 140 Ma. The 170–160 Ma rotation could has been triggered by the combined effects of the uncoupling of the Antarctic Peninsula, the high rates of subduction of the Phoenix plate beneath Patagonia, the opening of the Rocas Verdes basin and the Weddell Sea, and the cessation of the Tethys slab-pull. Furthermore, the calculated APWP for South America does not support a Jurassic massive true polar wander event.