University of Quebec at Montreal, Canada

The provenance of ice-rafted debris (IRD) found in marine sediment cores can be determined by matching the (super 40) Ar/ (super 39) Ar thermochronology of hornblende grains in the IRD to the thermochronology of the exposed areas of East Antarctica. However, even though there have been many thermochronologic analyses of the onshore exposures, most of the East Antarctic coastline is ice-covered, and the onshore metamorphic provinces are not all well delimited. Roy et al. (2007) found that the thermochronologic signature of IRD from circum-Antarctic marine core-tops defined several geographic sectors with distinct provenance signals, thereby providing a base map for fingerprinting sediment sources from the Antarctic margin. We have subsequently used this base map to find the provenance of IRD back to 19 million years ago at ODP Site 1165, offshore of Prydz Bay, revealing ice-rafting conditions sometimes very different to today, with icebergs transported westwards from as far as the Adelie coast (Williams et al., 2007). Together with new analyses of IRD in progress, the offshore data can help to refine the limits of the onshore metamorphic provinces.