PUTATIVE DEEP WEATHERING PROFILES IN THE ARCTIC

Weathered rock profiles are widespread throughout Europe, where they form blankets often >50 m thick, such as in the Scandinavian Mountains, Fennoscandian Shield, British Isles, and the central European mountain and upland belts. All of these are characterized by abundance of Mesozoic and Cenozoic geology weathered to kaolinite-rich saprolite. Remnants of deeply weathered basement rocks in Norway occur along structurally defined zones of crustal weakness, where locally-continuous saprolite layers can be up to 100 m in thickness. This likely had a substantial impact on the geomorphological evolution of the topography of Norway, since erosion of the sedimentary succession does not seem sufficient to explain the observed immature Alpine-type topography.

On the islands of Hadseløy and Hamarøy, two localities within the Arctic Circle of Norway, two sites were studied that display apparently deep weathering profiles up to ~30m thickness, containing relic boulders preserved at different stages of spheroidal weathering. Fresh samples yield andesitic and dacitic geochemical compositions. Mineral compositions comprise of plagioclase and potassium feldspar, varying from ~40-55wt% and ~25-30wt%, respectively, along with quartz 4-11wt%, and minor <3% vermiculite.

In both localities, samples contain Al₂O₃ at ~16wt%, Na₂O at ~5.0wt%, and CaO at ~2.0-2.8wt%. SiO₂/Al₂O₃ ratios vary from ~3.4 to 3.9, and TiO₂/Na₂O ratios display values from ~0.12-0.23 (for Hadseløy) and ~1.6-2.0 (for Hamarøy). Chemical Index of Alteration (CIA) clusters at ~50 in both localities. La/Ce, Y/Ba ratios display no significant variability at ~0.5-0.6 and ~0.01-0.04, respectively; and Zr/Sr ranges from ~0.6-2.5 and ~0.035 in Hadseløy and Hamarøy, respectively. Elemental ratios of mobile to immobile elements do not fluctuate throughout the profiles.

The Norwegian Arctic landscape displays pockets of deeply weathered profiles, which could represent the remnants of a formerly extensive weathered blanket. These weathered profiles could have been preserved in areas where glacial ice was not erosive or was stagnant. These saprolitic pockets could be the result of grusification of coarse-grained rocks developed on specific palaeolandscape features. Their relationship to weathering processes and climatic changes is uncertain.