Paleomagnetism of the late Neoproterozoic Blueflower and Risky formations of the northern Cordillera, Canada

Abstract

Paleomagnetic analysis of the Risky and underlying Blueflower formations at the top of the Neoproterozoic Windermere Supergroup in the northern Cordillera of Canada revealed several magnetic components of geological significance. Rock strata of the Blueflower locality in the Mackenzie Mountains yielded no primary remanence due to extensive "pyritization" and weathering. However, dolomitic rocks of the Risky locality in the eastern Wernecke Mountains, 250 km to the north, yielded a probable primary remanence. The remanence has a direction at D, I = 055°, −64° (N = 11 samples from 4 sites, k = 18, α95 = 11°) and pole at 007°E, 29°S (δp, δm = 14°, 18°), and indicates a paleolatitude of 46 ± 14°S. Comparison between poles from the Risky and the overlying Backbone Ranges and Ingta formations suggests a profound post-Risky unconformity. Three secondary components are also present. Component B in both the Blueflower and Risky units appears to be a thermal overprint, possibly related to Vendian rifting. Its respective direction in each unit is D, I = 062°, +77° (N = 4 sites, k = 143, α95 = 8°) and D, I = 064°, +56° (N = 6 sites, k = 21, α95 = 15°), yielding poles of 110°E, 64°S (δp, δm = 13°, 14°) and 142°E, 44°S (δp, δm = 15°, 21°). Component C, only found in the Risky, is attributed to Late Cambrian to Middle Ordovician extension and magmatism. Component D, which predominates in both formations, relates to late Mesozoic compression and to weathering.