Carboniferous basin in Holm Land records local exhumation of the North-East Greenland Caledonides: Implications for the detrital zircon signature of a collisional orogen

Abstract

Carboniferous strata of the Wandel Sea Basin unconformably overlie the Laurentian Precambrian crystalline rocks of the Caledonian hinterland at its northernmost exposures in Holm Land (~80°N). Complex zircon from an intermediate gneiss gives an upper-intercept age of 1878 ± 71 Ma, a protolith age which fits with the regional 1.8-2.0 Ga calc-alkaline arc. A strongly deformed pegmatite was intruded at 435 ± 17 Ma, and it is a rare example of Caledonian magmatism in the northern sector of the orogen. Omphacite confirms the presence of eclogite (sensu stricto) lenses in the basement complex, thus documenting the northern extent of the NorthEast Greenland eclogite province formed during the Caledonian collision with Baltica. Holm Land lies in the eastern block of the eclogite province, where an ultrahigh-pressure (UHP) meta morphic event took place at 365-350 Ma. Zircon from a Holm Land eclogite lacks a Eu anomaly, has a flat heavy rare earth element pattern, and gives a sensitive high-resolution ion microprobe U-Pb age of 423 ± 7 Ma, and it is thus interpreted as the time of high-pressure (HP) metamorphism. This age overlaps with the established age of widespread HP metamorphism for the eclogite province (i.e., 415-395 Ma), rather than the younger UHP metamorphism. Westward thrusting of the NorthEast Greenland eclogite province onto the Laurentian margin after 395 Ma and subsequent exhumation of this uppermost thrust sheet provided a substrate for Carboniferous deposition. Detrital zircon age spectra from arkosic sandstones of the late Viséan (ca. 330-340 Ma) Sortebakker and early Moscovian (ca. 310-315 Ma) Kap Jungersen Formations record the progressive unroofing of the NorthEast Greenland Caledonides. All seven samples have a major peak at 1.8-2.0 Ga, and five also have a 1.75 Ga peak, matching the Paleoproterozoic arc and later anorogenic granitoids that comprise the crystalline basement. Paleozoic grains are sparse in the Sortebakker sandstones, but they constitute a pronounced 400 Ma peak in the younger Kap Jungersen Formation. The composition of the detritusincluding garnet clasts, the high amount of discordant zircon (40%), and the large numbers of grains with metamorphic rims that cluster around 410 Ma-reflects a local provenance sourced in the NorthEast Greenland eclogite province, with some input from the overlying thrust sheets. Other Devonian and Carboniferous basins within and peripheral to the Caledonides also show distinct signatures, demonstrating that there is not a simple, representative detrital zircon signature for the Caledonian orogen.

Middle to Late Devonian–Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea

“…In well 7124/3-1 (Fig. 2), Asselian evaporite deposits typically include thin layers of anhydrite and gypsum, but thicker, halite-rich end-members are found along the flanks of the Nordkapp Basin and southwesternmost Nordkapp basin where large pillows of upper Carboniferouslower Permian salt were observed (Gabrielsen et al, 1992;Jensen and Sørensen, 1992;Koyi et al, 1993;Nilsen et al, 1995;Gudlaugsson et al, 1998;Koehl et al, 2017). In the Nordkapp Basin, pre-Permian deposits may in places reach a thickness of up to 7-8 km (Gudlaugsson et al, 1998).…”

“…Recent geophysical studies by Pastore et al (2016) show that the base of the Seiland Igneous Province defines two deep-reaching roots located below the islands of Seiland and Sørøya constraining the thickness of the Kalak Nappe Complex in this area to a maximum of 10 km. On the Porsanger and Varanger peninsulas, ENE-WSW-to NNE-SSW-trending Ediacaran metadolerite dyke swarms are particularly common, and they are associated with the rifting of the Iapetus Ocean as well (see Roberts, 1972;Siedlecka et al, 2004;Nasuti et al, 2015).…”

“…Roberts et al (1991) and Lippard and Prestvik (1997) presented indirect evidence of early Carboniferous dolerite dykes emplaced along and sealing WNW-ESE-trending brittle fault segments of the TKFZ on Magerøya, thus providing a minimum estimate for the latest stage of faulting along this fault. These dykes produce high positive aeromagnetic anomalies (Nasuti et al, 2015) and may be used to further identify brittle faults in NW Finnmark. Late Devonian dolerite dykes emplaced along brittle faults that trend NE-SW and N-S have been identified and dated on the eastern Varanger Peninsula (Guise and and on the Kola Peninsula (Roberts and Onstott, 1995).…”

“…In the Nordkapp Basin, pre-Permian deposits may in places reach a thickness of up to 7-8 km (Gudlaugsson et al, 1998). These deposits are composed of thick clastic sedimentary rocks and of upper Carboniferous to lower Permian evaporite deposits characterized by mobile salt that was involved in salt tectonism in the southwesternmost Nordkapp basin (Gudlaugsson et al, 1998;Koehl et al, 2017) and in the Nordkapp Basin (Gabrielsen et al, 1992;Jensen and Sørensen, 1992;Koyi et al, 1993;Nilsen et al, 1995).…”

Mid/Late Devonian-Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea

“…We propose that the SISZ and potential other Caledonian shear zones along the SW Barents Sea margin were inverted as low-angle extensional shear zones during late/post-Caledonian orogenic extension and subsequent collapse. This is based on analog examples in northeast Greenland (Sartini-Rideout et al, 2006;Hallett et al, 2014;McClelland et al, 2016), western Norway (Séranne & Seguret, 1987;1185Séranne et al, 1989Wilks & Cuthbert, 1994;Osmundsen & Andersen, 2001), mid-Norway (Braathen et al, 2000) and Lofoten-Vesterålen Steltenpohl et al, 2004;Osmundsen et al, 2005). Extensional reactivaton of such ductile shear zones along the Barents Sea margin might have initiated in the Early Devonian as in LofotenVesterålen (Steltenpohl et al, 2011), by crustal thinning and orogenic collapse through dominant 1190 top-to-the-NW displacement along the SISZ and later exhumation of the SISZ and underlying basement as a metamorphic core complex.…”