New Insights From Detrital Zircons Into the Northern Provenance of Triassic-Jurassic Strata, Sverdrup Basin, Canadian Arctic Islands
Rifting of landmasses to the north of the Sverdrup Basin in the Canadian Arctic during the Jurassic ultimately led to the onset of seafloor spreading and opening of the Arctic Ocean in the Cretaceous. While there is general consensus on the basic tenets of this geological evolution, details of the early rift history and the tectonic setting of the basin before the onset of rifting remain poorly understood, and as a consequence much debated. However the use of detrital zircons as provenance indicators may provide important insight into both these issues. New detrital zircon Uranium-Lead ages data from Lower Triassic to Lower Jurassic strata in this study combined with previously published U-Pb detrital zircon data from the Sverdrup Basin are sub-dividable into two distinct provenance signatures. The first consists of abundant Mesoproterozoic zircons sourced mostly from the Devonian Clastic Wedge located to the south. The second signature is sourced from the north and comprises a significant component of near syn-depositional Permo-Triassic ages with minor Mesoproterozoic relative age probability. Triassic strata of Arctic Alaska share this same dual provenance signature, whereas those in northeastern Russia (Chukotka) only exhibit the northern signature. The northern source to the Sverdrup Basin found in both Arctic Alaska and Chukotka has a broad spectrum of Permo-Triassic ages suggestive of continuous magmatism. Previous studies have suggested that the source of these ages could be the Siberian Traps and Urals; however, the former would produce too narrow a range of ages, and granitoids from the northernmost Urals are generally not younger than the Early Permian. Research here suggests a wholly different mechanism for the formation and location for Permo-Triassic zircons. It is suggested that zircons were sourced from an active margin north of the Sverdrup Basin, which previously was assumed to be passive. In rocks that are Early Jurassic and younger, the abundance of Permo-Triassic zircons decreases upward, implying the progressive diminution of the northern sediment source. The absence of these zircons in Lower Jurassic strata indicates the elimination of the northern sediment source, which quite possibly represents the onset of the rift unconformity – a surface previously reported to be Middle Jurassic, but in fact may be Early Jurassic.
AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016