Lithospheric Delamination as the Trigger for Eruption of Metasomatised Asthenospheric Magma in Northern Victoria Land, Antarctica Since Miocene

Cenozoic magmatism is widespread in northern Victoria Land and is associated with the development of West Antarctic Rift System. However, the petrogenesis of dykes and volcanic rocks and the significant time lag (several tens of million years) between extension and magmatism remain poorly understood. In this study, we evaluate the spatial and temporal variations in near‐primary basalt compositions, reconstruct the mantle source lithologies, and estimate the melting conditions based on the published data. Most of rocks are characterized by low CaO and Zr/Hf, high (Dy/Yb) N , (La/Yb) N , Fe/Mn and FCKANTMS, and high 143 Nd/ 144 Nd coupled with low 87 Sr/ 86 Sr, consistent with generation by about 5% partial melting of garnet pyroxenite in the asthenosphere, with a minor contribution from underlying garnet peridotite. Estimated temperatures (1252°C–1435°C) and pressures (1.1–2.9 GPa) increase systematically with decreasing age since around 12 Ma. The compositional variability indicates that the mantle source metasomatism predated Cretaceous rifting, whereas rift‐related extension was insufficient to induce the decompression and heating required for producing widespread volcanism. We propose that Miocene lithospheric delamination triggered efficient asthenospheric upwelling, leading to sequential melting of shallow pyroxenite followed by deeper peridotite and producing the large magma volumes responsible for the widespread volcanism in the region.