Ignition of the southern Atlantic seafloor spreading machine without hot-mantle booster

Abstract

The source of massive magma production at volcanic rifted margins remains strongly disputed since the first observations of thick lava piles in the 1980s. However, volumes of extruded and intruded melt products within rifted continental crust are still not accurately resolved using geophysical methods. Here we investigate the magma budget alongside the South Atlantic margins, at the onset of seafloor spreading, using high-quality seismic reflection profiles to accurately estimate the oceanic crustal thickness. We show that, along ~ 75% of the length of the Early-Cretaceous initial spreading centre, the crustal thickness is similar to regular oceanic thickness with an age > 100 Ma away from hot spots. Thus, most of the southernmost Atlantic Ocean opened without anomalously hot mantle, high magma supply being restricted to the Walvis Ridge area. We suggest that alternative explanations other than a hotter mantle should be favoured to explain the thick magmatic layer of seaward dipping reflectors landward of the initial mid-oceanic ridge.

2‐D Geodynamic Modeling of the Central South Atlantic Wide Rifted Margins, Implications for Evaporite Deposition

“…After crustal breakup, variations in oceanic crust thickness in the study area fall within the standard range (4-8 km) (Graça et al, 2019;Sauter et al, 2023) (Figure 4). This suggests the absence of a regional upper-mantle thermal anomaly at the time of crustal breakup.…”

Along-strike variation of volcanic addition controlling post breakup sedimentary infill: Pelotas margin, Austral South Atlantic

“…contrast, on land to the north, the distribution of Serra Geral coincides with that of the Palaeozoic Parana Basin. As discussed in Sauter et al (2023), this observed rapid decrease in magmatic volumes along strike may suggest that the large magmatic volumes observed in the north of the Pelotas margin (e.g., Torres High) are generated by a component of mantle inheritance rather than the usually assumed mantle-plume mechanism alone.…”

“…with breakup evolution being controlled by the Tristan mantle plume resulting in the Paraná-Etendeka magmatic province (Thompson et al, 2001;Peace et al 2020). In contrast, a more recent study by Sauter et al (2023) shows that the magmatic budget along large parts of the Austral segment does not need a hot-mantle booster and that higher magmatic budgets can only be observed north of the Chui-Cape Cross Fracture Zone when approaching the Paraná-Etendeka magmatic province. Sauter et al (2023) analysed, however, only the magmatic budget recorded in the first oceanic crust.…”

“…In contrast, a more recent study by Sauter et al (2023) shows that the magmatic budget along large parts of the Austral segment does not need a hot-mantle booster and that higher magmatic budgets can only be observed north of the Chui-Cape Cross Fracture Zone when approaching the Paraná-Etendeka magmatic province. Sauter et al (2023) analysed, however, only the magmatic budget recorded in the first oceanic crust. Important remaining questions are: do variations in magmatic addition occur along the Pelotas margin and, if variations do occur, how are they manifest in the margin architecture and how do they control margin accommodation space and depositional history.…”

Linking rifted margin crustal shape with the timing and volume of magmatism

“…Magma‐rich margins are sometimes associated with mantle plumes, which can produce advanced decompression melting with respect to crustal thinning due to higher asthenosphere temperature or increased water content. However, the observation of magma‐rich margins with thick SDRs and magmatic intrusion/underplate immediately followed by the first oceanic crust thinner than normal (e.g., Uruguay, N‐Argentina, Guyana; Sauter et al., 2023; Trude et al., 2022) implies that mantle plumes are not the only and/or most common cause of magma‐rich margins.…”