Paleomagnetic and Rock Magnetic Analysis of an Ignimbrite Sequence, the Yellowstone Huckleberry Ridge Tuff, Southeast Idaho

Abstract

Paleomagnetic data collected at four sites in ignimbrite members A and B of the Huckleberry Ridge Tuff in the Teton River Valley area of southeast Idaho, USA, yield ChRM directions in in situ coordinates of south-southwest declination and shallow inclinations that are consistent with previous investigations. Data collection was primarily focused on an exposure of HRT member A on a road cut off of Hog Hollow Road, where the ignimbrite was previously described as being an overturned fold that is reverse faulted. Contrary to this interpretation, the results of this study may imply that the Hog Hollow Road locality is not overturned, but is instead an upright fold that has been normal faulted. Data collected at the Hog Hollow locality indicate that folding and acquisition of compaction fabrics occurred above maximum magnetization blocking temperatures (>580ºC) in the hanging wall of faulted member A, but that deformation of underlying rocks occurred simultaneously with acquisition of remanence. Directional data from hanging wall and footwall rocks do not show significant deviations from each other to support an overturned fault, but instead support the hypothesis that the fold is an upright fold. Preliminary data from other sites may indicate that deformation followed ChRM acquisition at temperatures <580ºC thus during syn-emplacement-tilting.