REEVALUATING THE DISTRIBUTION OF THE LAVA CREEK TUFF, YELLOWSTONE
To begin the process of understanding the LCT eruption and its distribution, ignimbrite bulk samples were collected at six locations around the Yellowstone Caldera, with data from 22 preliminary samples presented here. Using physical descriptions and thin sections, we are able to visually distinguish four rock types based on glassy vs. devitrified matrix and crystal content. These varying characteristics of the LCT exhibit overlaps between members A and B as currently defined by Christiansen (2001). Additionally, we have not found amphibole in any of the samples examined thus far. Further, use of single-sanidine chemistry has found compositional dependence based on location, which has the potential to help restore eruption dynamics. These preliminary data suggest that LCT-A and -B are not as simple as previously thought and require reevaluation. Additional samples from seven localities along with single grain and melt chemistry will aid in our understanding of how the LCT is distributed around the park and if redefining the members is required.