| Summary: | Using geochemical, geochronological, geophysical, and field observations, we infer the presence of a previously unknown Miocene subglacial volcanic center approx. 230 km from the South Pole. Evidence of volcanism is from glacially deposited boulders of olivine bearing amygdaloidal/vesicular basalt and hyaloclastite in a moraine in the southern Transantarctic Mountains. 40Ar/39Ar ages from five specimens plus U-Pb ages of detrital zircons from glacial till indicate igneous activity 25-17 Ma. The most likely source is a circular, sharply defined -735 nT magnetic anomaly 60 km upflow from the sampling site. Subaqueous and subaerial textures of the volcanics indicate eruption beneath thin ice or at the margin of an ice mass during the early Miocene. These rocks record the southernmost Cenozoic volcanism in Antarctica and expand the known extent of the oldest lavas associated with West Antarctic rift system. They may be an expression of lithospheric foundering beneath the southern Transantarctic Mountains.
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