K-Ar dating: Late Cenozoic McMurdo Volcanic Group and dry valley glacial history, Victoria Land, Antarctica

K-Ar dates for 91 samples of subaerial volcanic rocks from the Transantarctic Mountains and islands in the Ross Sea range from 0'003 to 18'0 m.y., but most are less than 4 m.y. old; the few greater than 13 m.y. come from subaqueous eruption complexes or samples suspected of containing excess Ar. Ultramafic nodules and pyroxene xenocrysts contained in the volcanic rocks do contain excess radiogenic Ar. Excess Ar is indicated in several volcanic samples and is a matter of concern at all times. Nevertheless, most dates are reproducible on the same volcanic unit, stratigraphically consistent, and consistent with the paleomagnetic reversal time scale. Volcanism was not concentrated in a few major episodes. Eruptions occurred intermittently from scattered centres during a history of continental glaciation going back at least 4·6 my Uplift of the Transantarctic Mountains accompanied volcanism and glaciation and led to stagnation and retreat of a few of the outlet glaciers of the East Antarctic ice sheet, thus forming the dry valley systems near Ross Island. Although similar basalt-to-trachyte eruptive sequences are observed in different areas, each volcanic centre is unique in age and, except for the large complex central volcanoes, the lifetime of each centre was short.