THE PANTHER CREEK VOLCANO: A NEWLY DISCOVERED BASALTIC VENT IN YELLOWSTONE NATIONAL PARK

The Panther Creek Volcano (PCV) is a previously undescribed basaltic vent within the Pleistocene Swan Lake Flat basalt in the northwestern part of Yellowstone National Park. Located 1.8 km southwest of Swan Lake, this volcano is about 0.75 km in diameter. Basaltic eruptions have occurred throughout the history of the Yellowstone volcanic system (2.2 Ma to the present), but the youngest (<0.6 Ma) of these occur north of the caldera in the Norris-Mammoth corridor. The Swan Lake Flat basalt is the least eroded and most voluminous basaltic unit within the corridor. Typically basaltic eruptions within the Yellowstone Plateau were Hawaiian producing low-volume flows that resulted in small shields. Scoria and bombs observed near the summits of several of these shields suggest that eruptions cumulated with a Strombolian phase. The PCV is atypical within this volcanic field because its eruption style was primarily Strombolian. This eruption occurred in three phases. During the first phase, welded scoria and bombs produced a broad cone. Bombs are cored with partially melted “rhyolite” xenoliths. Lava flows with subtle banding erupted during phase 2. The flows can be traced as far as Indian Creek to the south and Swan Lake to the north. Some of these flows ponded in a lava lake in the summit crater of the cone. During the third phase welded scoria and bombs were again erupted. A 2.5-m wide composite dike on the northeastern side of the PCV may represent a feeder dike. The outer portion of the dike is massive, phenocrysts-poor basalt containing 4 to 25 cm diameter partially-melted granitic xenoliths. The inner portion of the dike is similar in texture and mineralogy but does not contain xenoliths. Overall, these tholeiites vary little in chemical composition; however, flows from the PCV are higher in Cr and lower in Ba and Rb compared to other Swan Lake Flat flows. Most importantly, with eNd values of -0.18 to 0.20, the PCV and its associated flows are the most primitive sampled in the park. This suggests that the partially-melted felsic xenoliths contributed little or no contamination to the unit. Because of increased activity within the Norris Geyser Basin there is renewed interest in volcanism in the Norris-Mammoth corridor. The Strombolian style of the Panther Creek volcano adds to the list of potential volcanic hazards in the NMC.