METEORITES AS SURFACE EXPOSURE TIME MARKERS ON THE BLUE ICE FIELDS OFANTARCTICA - EPISODIC ICE FLOW IN VICTORIA-LAND OVER THE LAST 300,000YEARS

Meteorites have been discovered in large numbers on certain blue ice f ields in the Antarctic. It is possible to estimate how long these mete orites have been on Earth using cosmogenic radionuclide abundances and , as discussed in this paper, how long they have been exposed on the i ce surface using natural thermoluminescence (TL) levels. In this paper we discuss two methods to determine surface exposure ages for Antarct ic meteorite finds; one method assumes an initial TL level and average surface exposure temperature while the other method uses multiple sam ples from a single meteorite and assumes a temperature gradient across the meteorite. The former method does not work for approximately 15% of meteorites which were heated prior to Earth impact. These data sugg est that no meteorite in the current study was exposed on the ice surf ace for more than 300,000 years, which may imply that the blue ice fie lds in question were not stable platforms prior to this point in time or that a rapid pulse in ice thickness cleared the field of meteorites . Steps in surface exposure ages suggest that accumulation of meteorit es on the ice fields has been episodic over the last 300,000 years, al though these episodes have been of lesser magnitude than that at about 300,000 years ago.