Abstract East–West Antarctic separation from ~43–11 Ma is well-documented through marine magnetic anomalies in the western Ross Sea, yet multiple lines of evidence suggest earlier extension, including Victoria Land uplift (~55–50 Ma) and reconstruction gaps between the Lord Howe Rise and Campbell Plateau. Here, we present marine magnetic data from the Central Basin between the Hallett Ridge and Iselin Bank revealing oceanic crust formed between Chrons 24–20 (~53–43 Ma), confirming earlier onset of East–West Antarctic motion. Forward modeling favors asymmetric extension as the preferred mechanism for forming the ~80 km wide Central Basin. This timing coincides with Transantarctic Mountains uplift and the termination of Tasman Sea spreading (~53 Ma), which redirected extensional forces southward along triple junction pathways into the Ross Sea. Our findings extend East–West Antarctic motion ~10 million years earlier than previously established, resolving the temporal discrepancy with Victoria Land uplift and reducing long-standing misfits in Southwest Pacific reconstructions.
Choi et al. (2026) studied this question.