Ice sheet development in Central Greenland: implications from the Nd, Sr and Pb isotopic compositions of basal material

The Nd, Sr and Pb isotopic compositions of silt particles from the basal silty ice of the two deep ice cores in Central Greenland, GISP 2 and GRIP, are compared to those of the subglacial rock material at GISP 2 (dolerite boulder, till and granitic bedrock). The silt particles embedded in the GRIP basal ice result from the reworking of the subglacial till unit overlying granitic bedrock at GISP 2, 28 km to the east. This implies that the till unit is continuous in Central Greenland. The silt particles embedded in the GISP 2 basal ice result from local erosion of the granitic bedrock. An erratic dolerite boulder in the subglacial till at GISP 2 is from a mafic dyke that can be related to the Carolinidian mid-Proterozoic fold belt exposed in East Greenland. This study supports the hypothesis that the Greenland Ice Sheet in the Summit area did not result from in situ growth from local snowbanks. The composition of the dolerite boulder points to East Greenland as the most probable source region for the ice sheet.