SPATIAL AND TEMPORAL PATTERNS OF NEOGENE BASALTIC VOLCANISM IN THE TRANSANTARCTIC MOUNTAINS, SOUTHERN VICTORIA LAND

Distinct patterns in the age and map distribution of 68 monogenetic basaltic volcanoes in the Transantarctic Mountains (TAM) of southern Victoria Land may be linked to glacial and/or tectonic events during the Neogene. Most of the volcanic outcrops are heavily eroded remnants of cinder and spatter cones that range in age from 14.6 to 0.25 Ma.

Age distribution analysis is based on more than 120 ⁴⁰Ar/³⁹Ar furnace step-heating analyses of groundmass samples, including replicate analyses of the same samples and analyses of multiple samples from the same volcanoes. The Miocene to early Pliocene interval from 14.6 to 4.0 Ma includes 10 separate eruptions, all in the Royal Society Range, which occurred in six isolated pulses. The Plio-Pleistocene interval from 4.0-0.25 Ma includes 58 eruptions. Eruptions were isolated to the Dry Valleys until 2.5 Ma, after which eruptions occurred concurrently in the Dry Valleys and Royal Society Range. Volcanism ceased in the Dry Valleys by 1.5 Ma and but continued at a high rate in the Royal Society Range. Statistical treatment of the data suggests that the eruptions occurred in distinct pulses, including 14 pulses between 2.6-1.1 Ma at intervals ranging from 0.33 to 0.05 Ma. The most significant pulses occurred at 2.6-2.5 Ma and 1.9–1.8 Ma.

The volcanic record is remarkably dominated by subaerial eruptions despite the long and presumably continuous history of ice-sheet and alpine glacier fluctuations. The absence of ice-volcanic interactions in this record of 68 eruptions may be causally linked to deglaciation, due to ice/seawater de-loading of the crust. This and other possible causal relationships are being evaluated in ongoing analysis of the volcanic, tectonic, and glacial records.