So, what is the present objective for Elise studying radar?
|Axel Heiberg Island in red.|
First, what are salt diapirs? Salt, and other evapouratitic deposits, tend to be less dense than the surrounding strata. Like oil rising through water, tectonic activity can mobilize evapourite deposits, causing large mounds of salt to rise upward through the overlying rock units. The result is dome-like deformation structures surrounding the diapirs of salt.
|Extent of Sverdrup Basin in the Canadian Archipelago|
Axel Heiberg Island almost exclusively part of the Sverdrup Basin. The Sverdrup Basin is a 12-15 km thick succession of strata dated from the Carboniferous up until the Eocene. The section of strata on Axel Heiberg is approximately 10 km thick; the thickest section of Mesozoic strata in the Sverdrup Basin. Approximately 100 diapirs have been found within the basin, of which 60 are exposed at surface. Three quarters of exposed diapris within the basin are located on Axel Heiberg Island. The diapirs composed of anhydrite, which is weathering to gypusum, and contain interbeds of brecciated carbonates. The basin has been subjected to numerous tectonic events, contributing to the rise of the diapirs. The basin was subject to rifting until the mid-Permian, and the basin thermally subsided between the late-Permian though the Early Jurassic. The older diapirs began their ascend during the Late Triassic, and were greatly accelerated by the onset of Arctic ocean seafloor spreading in the Cretaceous. During this time, rifting was accompanied by mafic dike swarms and flood basalt volcanism. The presence of minibasins surrounding the diapris provide evidence of regional shortening post-Late Cretaceous.
|Cross-section of evaporutic diaprism on western Axel Heiberg Island. Note the younger evapourite canopy in the WABS region, where two generations of diapirism has occurred (from Harrison and Jackson, 2006).|
Post-flood volcanism and other tectonic activies were more recent folding events. The deformation structures present are not very straight forward. Most of the region is characterized by sinusoidal folds, with anticlines and synclines equally wide. These trend to the north. However, Jackson and Harrison have found a 60 km wide area of deformation where shorter folds that are out of line with the surrounding region. This area, termed a wall-and-basin structure, contains a high abundance of diapirs. They hypothesize that the wall-and-basin structure represents a canopy, where rising diapirs came together, joining to form an stratiform sheet. The style of deformation indicates a possible detachment of the strata along the salt canopy. The abundant minibasins around the wall-and-basin structure is analogous to the Gulf of Mexico, where units have also subsided over large salt canopies.
Despite being well exposed in the polar desert, the rising evapourites on Axel Heiberg Island have not been well studied. Radar analysis and remote sensing are key tools in learning more about the geological behaviour of remote sites that are difficult to field check. In measuring the rate of movement within the Axel Heiberg diapirs, we can apply this knowledge to salt diapirs in other inaccessible areas, such as politically unstable countries, and other bodies in our solar system. Salt diapirs have both economic significances, as well as geological relevance in determine the stratigraphic relationships within a basin.
This is why we are doing what we are doing, time to learn some more radar! (After convocation this week.)