PROVENANCE OF THE CARBONIFEROUS BASIN IN HOLM LAND, NORTH-EAST GREENLAND

Carboniferous sedimentary units unconformably overlie eclogite-facies Paleoproterozoic basement gneisses in Holm Land, North-East Greenland and record exhumation of the Caledonian orogen. The Visean Sortebakker Formation contains arkosic sandstone with abundant gneissic lithic grains and a heavy mineral suite dominated by titanite, apatite and rutile but lacking garnet. ICPMS U-Pb ages on detrital zircon define dominant age groups at 1.75 and 1.98 Ga, broad peaks at 1.1-1.5, 2.2-3.0 Ga, and few Caledonian ages between 350 and 400 Ma. In contrast, Moscovian arkosic sandstone of the unconformably overlying Kap Jungersen Formation contains a heavy mineral suite of titanite, apatite, rutile, garnet, and epidote and gives ICPMS U-Pb detrital zircon ages of 390 Ma, 1.75 Ga and 1.98 Ga. CL imaging combined with ion probe U-Pb and trace element analysis demonstrate that low U rims on some zircons record Caledonian metamorphism.

The dominant peaks in all samples are most compatible with derivation from the underlying gneissic basement of the North-East Greenland eclogite province. The 1.75 and 1.98 Ga peak ages match the protolith age of the basement. The CL-bright, low-U metamorphic rims yield ages of 335 to 410 Ma that are consistent with metamorphic ages observed in the basement rocks. The large number of discordant grains observed in the detrital populations (23-47%) in all samples is similar to age spectra from basement samples as well. Grains that define broad peaks at 1.1-1.5, 2.2-3.0 Ga in the Sortebakker samples are interpreted to be from metasedimentary units in the structurally higher Caledonian nappes (e.g., Independence Fjord Group). These grains make up 30-35% of the population in the basal units, diminishing to 10% up section. The absence of the 1.1-1.5 and 2.2-3.0 Ga signature coupled with the sharp increase in number of Caledonian metamorphic grains and appearance of garnet indicate that the basal Kap Jungersen Formation lacked input from sources external to the underlying basement. Reappearance of the 1.1-1.5 and 2.2-3.0 Ga signatures higher in the section probably reflects recycling from the underlying Sortebakker section. Results of this study clearly demonstrate that a multifaceted approach to detrital zircon analysis greatly enhances characterization of provenance and depositional history.