Early rifting during marginal basin development: Petrography, microstructure, and detrital zircon U‐Pb geochronology of the Lapataia Formation, Argentine Fuegian Andes

Abstract

Although being one of the most efficient tools to constrain the stratigraphy of sedimentary basins, detrital zircon geochronology may present limitations under certain conditions, and isotopic ages should be treated with caution before assigning a depositional age. This is the case of depositional environments that lack coeval volcanism, where there may exist a significant time gap between the age of the youngest detrital zircon available and the actual time of deposition of a sedimentary rock. In this paper, we put on a comprehensive analysis in which detrital geochronology is aided with other reliable geological constraints. As a case study, we evaluate the stratigraphic age and provenance of the Lapataia Formation from the Fuegian Andes of southernmost South America, a low‐grade metamorphic unit with a problematic stratigraphic definition in the context of the Rocas Verdes basin. Detrital ages show very wide age spectra, with a younger peak at ca. 267 Ma. However, based on detailed petrography and microstructural observations, as well as stratigraphic correlations at a regional scale, we conclude that the Lapataia Formation represents the earliest stages of Jurassic rifting during the opening of the Rocas Verdes basin. Erosion from older basement blocks in an environment lacking coeval volcanic activity explains the occurrence of Paleozoic and older grains, and the lack of younger zircons. This work offers a multifaceted approach, which may be essential to assist radiometric detrital geochronology at certain stages during basin evolution.

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

“…Thus, due to the generalized NE-SW extension throughout southwestern Gondwana from the Middle Triassic to the Late Jurassic (e.g., Vizán et al, 2017), some rotations of blocks were conditioned by the pre-Jurassic structures from NW-SE to NNO-SSE direction (e.g., Uliana and Biddle, 1988). This extension, triggered by the Tethys slab pull (Vizán et al, 2017), and the high rates of subduction of the Phoenix plate beneath Patagonia plate in a southeastward direction (East et al, 2020), caused the migration of the Antarctic Peninsula towards the south and the opening of the Rocas Verdes basin (Bastias et al, 2019;Bastias et al, 2021;Cao et al, 2022;Jordan et al, 2020;Suárez et al, 2019;van de Lagemaat et al, 2021), and the beginning of the extension of the later Weddell Sea (Bastias et al, 2021;Jordan et al, 2020;Riley et al, 2020). Finally, the shear component on the extensional stresses which affected Patagonia ceased around 157 Ma, wich could be related to the end of the Tethys slab pull (Fig.…”

“…Furthermore, this continental migration between 200 Ma and 170 Ma coincides with the back-arc extension in the Weddell Sea rift system proposed by Jordan et al (2020) and Riley et al (2020) and the uncoupling of the Antarctic Peninsula (Bastias et al, 2019;Bastias et al, 2021;Suárez et al, 2019;van de Lagemaat et al, 2021). The apparent rotation of the continent (170-160 Ma) may be related to the combination of different tectonic events: 1) the cessation of the northeastward extensional stresses caused in part by Tethys slab-pull (160 Ma; Vizán et al, 2017), 2) the southward migration of the Antarctic Peninsula (Bastias et al, 2019;Bastias et al, 2021;Suárez et al, 2019;van de Lagemaat et al, 2021), 3) the opening of the Rocas Verdes Basin (Calderón et al, 2016;Cao et al, 2022;Muller et al, 2021;Ronda et al, 2019), and 4) the Weddell Sea rifting system (Jordan et al, 2020;Riley et al, 2020). Moreover, these events were controlled by the high rates of subduction of the Phoenix plate (East et al, 2020), which generated the predominance of the extensional stress in the SSW direction (Fig.…”

“…Since the Triassic period, the overall tectonic regime along Pangea was extensional, which triggered the formation of the accommodation space of the Mesozoic basins and, finally, the supercontinent breakup (e. g., Vizán et al, 2017). In Gondwana, this extensional regime could be related with the collapse of the Godwanides (e.g., Kern et al, 2021;Ramos, 2008), the later opening of the Weddell Sea and the Rocas Verdes Basin during the Early-Middle Jurassic (e.g., Bastias et al, 2021;Calderón et al, 2007;Cao et al, 2022;Dalziel et al, 1974;Ferris et al, 2000;Ghidella et al, 2002;Grunow, 1993;Grunow et al, 1987;Jordan et al, 2017Jordan et al, , 2020König and Jokat, 2006;Riley et al, 2020;Suárez et al, 2019), and finally with the opening of the South Atlantic Ocean since the Early Cretaceous (e.g., Creer et al, 1972;Eagles, 2007;Nürnberg and Müller, 1991;Schult and Guerreiro, 1979;Torsvik et al, 2009). Furthermore, the regional crustal thinning and the associated uplift of the asthenosphere (e.g., Huang et al, 2019;Zhong et al, 2007), aided in the formation of Large Igneous Provinces such as the felsic Chon Aike Igneous Province (198-145 Ma;Kay et al, 1989), the mafic Paraná-Etendeka Magmatic Province (130-132 Ma; Renne et al, 1992) and the Central Atlantic Magmatic Province (190-202 Ma;May, 1971).…”