9316289 Nash Our preliminary data and the results of other workers indicate that during the 16 Ma evolution of the Yellowstone thermal anomaly the frequency of eruption has varied significantly, as has the temperature, chemical and isotopic composition of magmas. This proposed study intends to examine each of these parameters within a well constrained temporal framework. The PIs proposed to collect and analyze tephra erupted during the evolution of the Yellowstone thermal anomaly in order to: 1) Measure the frequency and volumes of explosive eruption, assess possible periodicity in eruption rate, and evaluate suggested gaps in explosive activity; 2) Determine the major and trace element chemical composition of glass and phenocrysts; 3) Use mineral thermometers to determine temperatures of magmas; 4) Measure Nd and Sr isotopic ratios to determine relative input of mantle and crustal sources into the silicic magma generating system, and to record the effect of eastward translation of the thermal anomaly from accreted oceanic ltihosphere to the continental craton. This study will provide an integrated investigation of the evolution of the major thermal anomaly and should lead to a better understanding of the interaction of this type of heat source with the continental lithosphere.
