Timing and geometry of early Gondwana breakup

Abstract

[1] The Mesozoic opening history of the Southern Ocean between South America, Africa, and Antarctica is one of the largest gaps in knowledge on the evolution of this region. Competing geodynamic models were published during the last two decades to explain the geophysical and geological observations. Here we report on aeromagnetic data collected along the East Antarctic coast during five seasons. These data provide new constraints on the timing and geometry of the early Gondwana breakup. In the Riiser-Larsen Sea/ Mozambique Basin, the first oceanic crust between Africa and Antarctica formed around 155 Ma. In the west the Weddell Rift propagated from west to east with a velocity of 63 km/Myr between chrons M19N and M17N. At chron M14N, South America and Africa finally were split off the Antarctic continent. Stretching in the area of the South Atlantic started at the latest from 155 Myr onward. The different spreading velocities and directions of South America and Africa created at chron M9N the first oceanic crust in the South Atlantic. A new model indicates that the Karoo and Dronning Maud Land magmatism occurred well before any new ocean floor was created and therefore the first formation of new oceanic crust cannot directly be related to a plume interaction.

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“…The complex tectonic development of the Weddell Sea sector (Figure 2) has more recently been reconstructed by Hübscher et al (1996a), Jokat et al (1996Jokat et al ( , 1997Jokat et al ( , 2003Jokat et al ( , (1996a, Jokat et al (1996Jokat et al ( , 1997Jokat et al ( , 2003Jokat et al ( , 2004, Leitchenkov et al (1996), Ghidella and LaBrecque (1997), Golynsky and Aleshkova (2000), Ghidella et al (2002), Rogenhagen and Jokat (2002), and König and Jokat (2006). Deciphering of the crustal types in the central Weddell Sea is still hampered by the lack of deep crustal seismic data.…”

“…The recent plate-kinematic reconstructions by Jokat et al (2003) and König and Jokat (2006) show that southeast Africa was conjugate to the DML margin ( Figure 3) from just east of the Explora Escarpment to the Gunnerus Ridge. However, this DML margin has two distinct parts, separated by the Astrid Ridge.…”

“…Data and syntheses of the central and eastern Dronning Maud Land (DML) margin stem from work by Hinz and Krause (1982), Hübscher et al (1996b), Roeser et al (1996b), Roeser et al (1996), Jokat et al (2003Jokat et al ( , 2004, Hinz et al (2004), and, and König and Jokat (2006). The recent plate-kinematic reconstructions by Jokat et al (2003) and König and Jokat (2006) show that southeast Africa was conjugate to the DML margin ( Figure 3) from just east of the Explora Escarpment to the Gunnerus Ridge.…”

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“…Aeromagnetic data collected by the AWI along the eastern Weddell Sea and Riiser-Larsen Sea continental margins provide new constraints on the timing and geometry of the early Gondwana breakup (Jokat et al, 2003).…”

“…One of the largest aeromagnetic datasets was collected by the Alfred Wegener Institute (AWI) over western Dronning Maud Land (DML) and its continental margin since the austral summer of 1996/97 (Jokat et al, 2003). Within the East Antarctic Margin Aeromagnetic and Gravity Experiment (EMAGE) project, a total of 90,000 km of aeromagnetic data were acquired along a 1200 km long segment of the East Antarctic coast.…”