PALEOMAGNETIC INVESTIGATIONS OF PEACH SPRINGS TUFF (PST) AND OTHER PRE-EXTENSIONAL IGNIMBRITES IN THE COLORADO RIVER EXTENSIONAL CORRIDOR, LAUGHLIN, NV TO KINGMAN, AZ REGION

This study analyzes paleomagnetic data of PST and other similar-age ash-flow tuff units in the Colorado River Extensional Corridor in the vicinity of Laughlin, NV to Kingman, AZ. Correlation and discrimination of these units is critical in this part of the Basin and Range Province as they provide important pre-extensional, paleohorizontal horizons. Tuff samples were collected along the western edge of the Cerbat Mtns. (CM) and in the Grasshopper Junction (GHJ) and Warm Springs (WS) regions of the southern Black Mountains. Results reported here are preliminary and include only data from alternating-frequency demagnetization experiments. Thermal demagnetization experiments and anisotropy of magnetic susceptibility results are forthcoming. In the WS region, at the southern tip of the Black Mountains, two thick sections of highly welded tuff are separated by several meters of intervening fluvial sandstone and basalt; previous mapping had combined both of these units into the PST. Our paleomagnetic data indicate a likely correlation the upper tuff in this area to the PST while the lower welded unit has remanence directions similar to those defined by us for the Cook Canyon Tuff (CCT) at its type section near Kingman. Additionally, at WS the CCT is more welded and thicker than at Kingman suggesting that WS is closer to the CCT's source. GHJ tuffs tentatively correlate with the PST; the CCT does not appear to be present in the GHJ region as evidenced by dissimilar mineralogies and paleomagnetic directions. However, GHJ tuffs yield remanence directions that vary between Wells and Hillhouse's (1989) PST reference direction and the average Miocene pole direction. This difference does not appear to be linked to slower cooling rates in thick sections as Wells and Hillhouse (1989) suggested. We propose a temporal origin of this aberration; that the PST eruption may have occurred over a longer time period with a rapidly shifting magnetic pole position. Basal tuff in the CM does not correlate paleomagnetically to either the CCT or to the PST.