Anomalous Cenozoic Post-Rift Uplift in the North Atlantic; The Role of Mantle Plumes, Transform Margins and Propagating Rifts
Tuesday, 16 December 2014
Under classic tectonic theory sedimentary basins and continental margins are expected to experience rapid tectonic subsidence during times of active extension and then slow as subsidence becomes controlled by cooling and thickening of the mantle lithosphere after the end of extension. Subsidence has departed from this simple model in the NE Atlantic because of the temporary buoyant effects of upwelling mantle plumes (e.g., Iceland and that responsible for the emplacement of the Yermak Plateau), with this extra uplift dissipating as the plate move away from the area of upwelling. Permanent uplift has been caused by regional magmatic underplating, again often linked to melting from a plume. Svalbard in particular is anomalous in that it constitutes one of the few subaerial parts of the submarine shelf area of the Barents Sea and had also been affected by transpressional deformation resulting in the formation of the West Spitsbergen Foldbelt (WSFB). One and two-dimensional subsidence analyses were used to quantify and date phases of uplift during the Cenozoic. Svalbard has experienced two phases of uplift, from >36 to ~10 Ma, and since ~10 Ma, which is similar in timing to uplift phases identified in Greenland, Scandinavia and the Barents Shelf. Total uplift across much of the Central Tertiary Basin of Svalbard is >1.5 km and exceeds 2.5 km in parts of the WSFB. Uplift from >36 to ~10 Ma accounts for the greatest part of the vertical motion and like the younger phase reduces in magnitude towards the east. Flexural rigidity of the lithosphere is estimated to be low (Te ≈ 5 km), so that erosion of the WSFB after 36 Ma contributes little to the total amount of uplift. The permanent nature of uplift and the proximity to the Yermak Plateau implies that regional magmatic underplating is the cause of uplift. Plume dynamic support and flexural unloading along the western transform margin of the Eurasian plate can be ruled out as significant influences on vertical motions. The second phase of uplift since ~10 Ma that generated the modern topography may be linked to thermal erosion of the mantle lithosphere under Svalbard. We suggest that a likely cause of much of the surface uplift is the northward propagation of the Knipovich Ridge to establish continuous seafloor spreading through the Fram Strait after ~10 Ma.