A BACKARC TO RETROARC REGIME FOR THE SVERDRUP BASIN DURING THE LATE PALEOZOIC

The Sverdrup Basin of the Canadian Arctic Islands has long been interpreted to be a peri-cratonic rift located between the Laurentian margin, to the south, and enigmatic terranes to the north. However, new stratigraphic, structural and geochronological evidence from Pennsylvanian to Triassic strata challenges this interpretation and supports a backarc to retroarc setting.

Crustal thinning that led to the development of the Sverdrup Basin during the Mississippian was followed by at least five episodes of basin inversion during the latest Pennsylvanian and Permian. Basin inversion was often accompanied by mafic volcanism and the onset of northerly derived terrigenous material from terranes adjacent to the basin before opening of the Amerasia Basin. These terranes now lie beneath post-Jurassic strata and thus the characteristics of the northern sediment sources and their relation to the basin inversion events in the Sverdrup Basin remain unexplored.

Field observations on the northwestern portion of the basin identify polyphase folds that are truncated by three angular unconformities in Pennsylvanian to uppermost Permian strata, along with locally-derived conglomeratic deposition bounding each stratigraphic sequence, suggesting significant uplift during these events. Stratigraphic sections of abnormally thin Permian strata further reveal that the area was uplifted multiple times during this period. Additionally, Permian to Lower Triassic units yield detrital zircon populations that include syn-depositional grains within an isolated 295-250 Ma population.

These data support the presence of a tectonically and magmatically active region north of the Sverdrup Basin during the late Paleozoic and are best explained by the development of a magmatic arc north of the basin in the Pennsylvanian to Permian. We propose a model in which the Sverdrup Basin constitutes the continental portion of a backarc basin developed between the Laurentian margin and Chukotka, one of the northern terranes. The closure of this backarc basin in the latest Pennsylvanian produced a magmatic arc adjacent to the Sverdrup Basin. As such, the basin was located in a retroarc setting until the Triassic, and late Paleozoic deformation and magmatism could have been related to changes in plate boundary conditions to the north of this magmatic arc.