The big flush: paleomagnetic signature of a 70 Ma regional hydrothermal event in displaced rocks of the northern Canadian Cordillera

Abstract

The 70 Ma Carmacks Group, a subaerial volcanic succession which once covered much of central southwest Yukon, has a paleomagnetic remanent direction which passes the fold test and the reversal test. A new collection of 13 sites, combined with 13 sites from a previous study, renders a pole (088.6°E, 78.4°N, A95 = 7.8°) which is far-sided with respect to the pole for cratonic North America and implies a displacement from the south of 1900 ± 700 km. Late Triassic Mandanna Member red beds and Early Jurassic Nordenskiöld Formation tuffs, deformed in the Late Jurassic, fail the fold test and conglomerate test but pass a contact test with Eocene dykes. The postdeformational remanent direction is identical to that isolated from the Carmacks Group. The magnetic signature contained in these older formations is probably an overprint produced by an extensive hydrothermal system active during Carmacks extrusion. Geological work indicates that the Carmacks Group is plume related. Given its paleomagnetic latitude and geological nature, we hypothesize that the Carmacks Group is a displaced segment of the Yellowstone hot-spot track, and the hydrothermal system which remagnetized the older rocks was established by mantle upwelling below the region.