MESOZOIC REGIONAL STRESS FIELD EVOLUTION IN SVALBARD

During most of the Mesozoic, Svalbard on the northwest portion of the Barents Shelf was in an intraplate setting characterized by continental platform sedimentation. This was interrupted by activity associated with the early Cretaceous age High Arctic Large Igneous Province (HALIP) along with development of the Amerasian Basin to the present north, and subsequent Paleocene transpression with Greenland forming the West Spitsbergen fold-thrust belt to the west. Cooling fractures in widespread HALIP diabase sills and syn-sedimentary Triassic faults provide an opportunity to obtain geologic snapshots of the likely contemporaneous ambient stress field in the area. Sill fracture orientation and trait data were collected from multiple sites at two areas ca. 150 km apart within Svalbard, central Spitsbergen and Edgeøya. The Central Spitsbergen sill fractures show a more complicated pattern/history due to a strong Paleocene Tertiary overprint and complex intrusion geometries. A distinct ENE-WSW oriented set is associated with sill cooling. The sill fracture patterns from Edgeøya are simpler, and those associated with cooling are aligned with their central Spitsbergen counterparts. Together they indicate that a regional Cretaceous stress field existed with the minimum horizontal stress in a NNW-SSE direction. These directions are distinctly oblique to earlier more N-S Paleozoic structural grains. Distributed syn-sedimentary Triassic faults imply an earlier, but small scale, extension and an inferred minimum horizontal stress in a NNE-SSE direction in the Edgeøya and Hopen areas. Both fractures systems suggest a persistent Mesozoic broadly north-south minimum horizontal stress that rotated counter clockwise with time. Triassic extension in eastern Svalbard was highly oblique to the direction of ongoing crustal thickening in Novaya Zemlya to the east, suggesting far field and mild indenter tectonics may have been at play. The Cretaceous fracture direction is roughly aligned with the Lomonosov and Alpha ridges, suggesting linkage between an existing intraplate stress field, HALIP and Amerasian basin formation. Paleocene dextral transpression between the Barents Shelf and Greenland is broadly consistent with continued counter clockwise rotation of stress directions with time.