RELATION BETWEEN SALT DIAPIRISM AND THE TECTONIC HISTORY OF THE SVERDRUP BASIN, ARCTIC CANADA

The Sverdrup Basin is a pericratonic sedimentary trough in northern Ca nada containing up to 13 km of Carboniferous to Tertiary strata. The b asin formed by late Paleozoic continental rifting and was subsequently affected by a series of alternating tectonic settings. Evaporite diap irs are well exposed at the present erosion level and occur mainly alo ng the basin axis. The diapiric source layer consists of about 400 m o f anhydrite underlain by salt of unknown stratigraphic thickness, depo sited during the initial Permo-Carboniferous synrift phase of basin su bsidence. Large salt-anhydrite diapirs rose into the sedimentary overb urden when the overburden had reached a thickness of several kilometre s. They grew during a relatively long period of modest horizontal comp ression from the Permo-Triassic to Early Cretaceous. Much smaller, tab ular anhydrite diapirs were rapidly emplaced during periods of high ho rizontal compression, in the middle Cretaceous, when large flexural st resses were induced by sedimentary loading, and during the early Terti ary when high intraplate compression resulted from far-field tectonic forces during the Eurekan orogeny. The diapiric behaviour of dense anh ydrite implies that buoyancy alone was incapable of driving the diapir ism in the Sverdrup Basin. The importance of other driving forces, suc h as differential loading, basement or overburden faulting, extension, and thermal convection, is thought to be secondary. This suggests a c orrelation between diapirism and periods of significant horizontal com pression, implying that plate-tectonic forces and flexural loading are important driving mechanisms of evaporite diapirism in the Sverdrup B asin.