Refinement Of The Late Quaternary Geologic History Of Erebus Volcano, Antarctica Using ~(40)ar/~(39)ar And ~(36)cl Age Determinations

摘要

Six new ~(40)Ar/~(39)Ar and three cosmogenic ~(36)Cl age determinations provide new insight into the late Quaternary eruptive history of Erebus volcano. Anorthoclase from 3 lava flows on the caldera rim have ~(40)Ar/ ~(39)Ar ages of 23 ± 12, 81 ±3 and 172±10 ka (all uncertainties 2cr). 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 ~(36)Cl ages are the first exposure ages reported for rocks from Erebus volcano. At an assumed erosion rate of 1.5 mm/ka ~(36)Cl 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 ~(36)Cl ages overlap within analytical uncertainty or are slightly younger than ~(40)Ar/~(39)Ar 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.