STRUCTURAL GEOLOGY OF WRANGEL ISLAND, ARCTIC RUSSIA

Wrangel Island is a unique exposure of Neoproterozoic basement and its overlying cover near the Bering Strait. Its geology and structural evolution are critical for testing geologic continuity between Alaska and Russia and for constraining plate reconstructions of the Arctic. Based on detrital zircon studies, its upper Paleozoic section correlates with that of the Hannah Trough and North Slope of Alaska. Wrangel lies at the north end of the Herald Arch and are depicted as the northernmost continuation of the Brooks Range fold-and-thrust belt. However, the style and timing of deformation on Wrangel Island differs from that of the Late Jurassic to Early Cretaceous Brooks Range and its equivalent, the Chukotka fold belt. Earlier deformation(s) on Wrangel are overprinted by penetrative metamorphic fabrics that increase in grade and degree of strain with depth. Foliation strikes E-W, dips ~30-40° S with a pronounced N-S stretching lineation. Aspect ratios of stretched pebbles are ~ 5:1:0.2 to 10:1:0.1. Foliation is axial planar to mostly E-W tight/isoclinal folds (at all scales). Oriented thin-sections of sandstones, shales, feldspathic sandstones and grits indicate deformation by flattening perpendicular to foliation but sense of shear indicators in lineation direction are absent or mixed. Quartz fabrics and microstructures and the assemblage chlorite + white mica (with growth of biotite at deepest structural levels) suggest deformation between about 350° and 450°C. Preservation (rather than annealing) of quartz microstructures suggests deformation during uplift/cooling rather than burial/heating. Apatite fission track (AFT) ages of 7 samples from a 9 km N-S transect yield statistically indistinguishable ages ~ 95 Ma interpreted as time of cooling below ≈100°C during erosional unroofing. Instead of being related to regional folding and thrusting, it is more likely that deformation on Wrangel Island was coeval with syn-extensional magmatism along the Russian coast dated at 105-100 Ma. As such, its penetrative fabrics are more similar to syn-magmatic, extension-related fabrics developed in the Bering Strait region and along the southern flank of the Brooks Range, perhaps offset from them by right-lateral motion along the Herald Arch.