TRACING LOBES OF THE LAURENTIDE ICE SHEET IN INDIANA USING DETRITAL ZIRCON AGE DISTRIBUTIONS

U/Pb age distributions of detrital zircon populations are being tested as a provenance indicator of glacial till. Detrital zircons were separated from till from the Valparaiso Moraine of the Lake Michigan Lobe, the Mississinewa Moraine of the Huron-Erie Lobe, the Kalamazoo Moraine of the Saginaw Lobe, and the Tipton Till Plain to determine the variability of till within and between different lobes. Comparisons between the detrital zircon age distributions of each sample indicate that there is some minor variability between the detrital zircon age distributions within the Valparaiso Moraine and the Mississinewa Moraine. Furthermore, the detrital zircon age distributions from the Lake Michigan and Huron-Erie Lobe tills are distinct from each other; the Lake Michigan Lobe has larger populations of Superior Province (>2500 Ma) and Granite-Rhyolite Province grains (1300-1600 Ma), and the Huron-Erie Lobe has a larger population of Grenville Province grains (950-1300 Ma). The Saginaw Lobe till has a larger population of <950 Ma grains than the other tills but is otherwise similar to the Huron-Erie Lobe till. Because the Lake Michigan and Huron-Erie Lobe tills have unique age distributions and were assumed to be the only sources for the Wisconsinan till of the Tipton Till Plain, their age distributions were used in a mixing model to approximate how much each lobe and an unknown factor may have contributed to the Tipton Till Plain. The mixing model shows only the Huron-Erie Lobe and an unknown source contributed to all samples in the till plain except for the westernmost sample in this study, which has approximately equal Lake Michigan and Huron-Erie Lobe influence. The unknown source contains a higher proportion of Grenville zircons than the three lobes. The current hypothesis is the Teays River sediment contained Grenville detrital zircons, and the ice sheet incorporated Teays sediment south of the recessional moraines.