Towards better Greenland source attribution for IRD via Pb in feldspar and Ar-Ar in amphibole

The provenance of Ice rafted debris, IRD, deposited in marine sediments has great potential to fingerprint regions of present and past iceberg calving in the coastal zones of continental margins. In particular, the growth of the Greenland Ice Sheet during the Pliocene intensification of northern hemisphere glaciation (and perhaps earlier) could be tracked by studying IRD in well-dated deep sea drill cores. However, the IRD record is only as strong as the onshore land-based record of potential sources. Two minerals common within IRD that have been used previously and that show great promise in this regard are feldspar and amphibole. Pb isotopes in feldspar record a diagnostic signature of the continental crust within distinct geologic terranes. In particular, Greenland is composed of a number of distinct terranes with proven distinct Pb isotope signatures. Ar-Ar dating of amphiboles records the thermal history of a terrane when it was metamorphosed above or cooled below c.550oC. Due to distinctive metamorphic histories within different terranes this signature is also potentially diagnostic of a particular source area. The two minerals together could be particularly powerful but only if the potential areas of calving are well-characterised. Here we present data form fluvio-glacial sediments from sites around the margins of Greenland and discuss their diagnostic characteristics. We also apply the principle to some circum-Greenland core top IRD samples and Mid Pliocene IRD from ODP Site 907.