THE CARBONIFEROUS WANDEL SEA BASIN IN HOLM LAND RECORDS LOCAL SYN- TO POST-OROGENIC EXHUMATION OF THE NORTH-EAST GREENLAND CALEDONIDES

Hinterland basins, such as the Devonian to Carboniferous basins of the Caledonides, commonly record syn- to post-orogenic sedimentation that can be tied to exhumation of the orogen in much the same way as classical foreland basins. In Holm Land (≈80°N), Carboniferous strata of the Wandel Sea basin rest unconformably on Laurentian gneisses of the Caledonian hinterland. We document that the gneiss contains the northernmost eclogites in NE Greenland, and that zircon from a gneiss gives an U-Pb upper intercept age of 1878 ± 71 Ma, consistent with similar Laurentian protoliths in the region. The age of eclogite facies metamorphism—from U-PB SIMS analysis of zircon with a flat HREE pattern and no Eu anomaly—is 423 ± 7 Ma. This age overlaps with the established age of widespread high-pressure metamorphism in the basement (i.e. 415–395 Ma), rather than later ultrahigh-pressure metamorphism (UHP) at 365–350 Ma. Westward thrusting of the NE Greenland eclogite province after 395 Ma and subsequent exhumation provided a substrate for deposition of the Wandel Sea basin.

Arkosic sandstones of the upper Viséan (ca. 330–340 Ma) Sortebakker and lower Moscovian (ca. 310–315 Ma) Kap Jungersen Formations have detrital zircon signatures that record the progressive unroofing of the Caledonian hinterland. The prominent Serpukhovian unconformity between these two formations may be related to exhumation of the UHP rocks. Data from 7 samples, including the presence of garnet clasts, the high amount of discordant zircon (40%), the large number of zircons with metamorphic rims that cluster around 410 Ma, and major peaks at 1.8–2.0 and 1.75 Ga, reflect a local provenance sourced in the NE Greenland eclogite province. The Wandel Sea basin in Holm Land is, therefore, an example of the provenance to be expected from the northeastern Greenland Caledonides. This signal is different than that recorded in the southern part of the Greenland Caledonides, the Norwegian Caledonides and other Devonian to Carboniferous basins in the region. Detrital zircon signatures from hinterland basins can be a proxy for collisional orogens where the foreland basin data is unavailable; however, the local variation observed among hinterland basins in a single orogen suggests that the foreland basin better characterizes the overall detrital zircon signature of an orogen.