Refinement of the late Quaternary geologic history of Erebus volcano, Antarctica using 40Ar/ 39Ar and 36Cl age determinations

Abstract

Six new 40Ar/ 39Ar and three cosmogenic 36Cl age determinations provide new insight into the late Quaternary eruptive history of Erebus volcano. Anorthoclase from 3 lava flows on the caldera rim have 40Ar/ 39Ar ages of 23 ± 12, 81 ± 3 and 172 ± 10 ka (all uncertainties 2 σ). The ages confirm the presence of a second, younger, superimposed caldera near the southwestern margin of the summit plateau and show that eruptive activity has occurred in the summit region for 77 ± 13 ka longer than previously thought. Trachyte from “Ice Station” on the eastern flank is 159 ± 2 ka, similar in age to those at Bomb Peak and Aurora Cliffs. The widespread occurrences of trachyte on the eastern flank of Erebus suggest a major previously unrecognized episode of trachytic volcanism. The trachyte lavas are chemically and isotopically distinct from alkaline lavas erupted contemporaneously in the summit region < 5 km away. The three 36Cl ages are the first exposure ages reported for rocks from Erebus volcano. At an assumed erosion rate of 1.5 mm/ka 36Cl cosmogenic ages are 6.0 ± 0.5 ka for the Ice Tower Ridge flow, 4.9 ± 0.4 ka for Lower Hut flow, and 6.5 ± 0.6 ka for the Northeast flow. The 36Cl ages overlap within analytical uncertainty or are slightly younger than 40Ar/ 39Ar ages for these lava flows, and confirm the overall young age (< 25 ka) of the summit lava flows. One interpretation of these uniformly young ages is that older eruptions infilled the topographic depression caused by caldera formation and subsequently was covered by younger lavas.