Anders Mattias Lundmark

Ordovician to Silurian magmatism on the Utsira High, North Sea: implications for correlations between the onshore and offshore Caledonides

Abstract The age and tectonic significance of two basement granitoids cored on the Utsira High, Viking Graben, North Sea, are constrained by zircon LA-ICPMS data. Syenite in well 25/10-2R is dated to 482±2 Ma, with ϵHf(482) values from −4.4 to −5.8, and granite in well 16/1-12 yields an age of 436±3 Ma with ϵHf(436) values from +3.7 to −0.5. The evolved Hf-signature of the syenite demonstrates 482 Ma reworking of Palaeoproterozoic–Archaean crust, interpreted to reflect Taconian–Grampian orogenesis. New and recently published data from the offshore Caledonides allow a first-order correlation of the Utsira High basement with the surrounding on- and offshore Caledonides. The Utsira High occupies a similar position with respect to Dalradian rocks as the Scottish Midland Valley terrane. Geophysical data indicate a volcanic arc beneath the East Shetland Basin, forming a northwards continuation of the Utsira High basement. We propose that the offshore volcanic arc segments represent the northeastern continuation of the Scottish Grampian orogen across the Mesozoic North Sea rift. A north-striking terrane boundary fault is proposed to separate the volcanic arc from the East Shetland Platform and merge northwards with the offshore extension of the Great Glen Fault–Møre Trøndelag Fault Complex. Supplementary material: U–Pb and Lu–Hf isotopic data are available at http://www.geolsoc.org.uk/SUP18705.

Provenance of late Palaeozoic terrestrial sediments on the northern flank of the Mid North Sea High: detrital zircon geochronology and rutile geochemical constraints

Abstract Zircon U–Pb and rutile trace element data are used to investigate the provenance of late Devonian to early Permian terrestrial sandstones in the Embla and Flora oil fields on the north flank of the Mid North Sea High, central North Sea. Two Old Red Sandstone samples (ORS 1) are dominated by 1.2–0.9 Ga Grenvillian zircons and low- to medium-grade rutile, with sparse Cambro-Ordovician Caledonian zircons (2–4%) and high-grade rutiles (0–5%). The samples are interpreted as recycled metasediments from the Scottish Caledonides. Two other Old Red Sandstone samples (ORS 2) contain a high proportion of Caledonian, mainly Silurian zircons (15–19%) and high-grade rutiles (15–18%); we propose that these components are traceable to the Krummedal sequence on East Greenland (and related sediments). We interpret the data to reflect a temporal evolution of the regional drainage system from northwestern to northeastern sources, with high-grade detritus reaching the Mid North Sea High in the Famennian–early Carboniferous. A late Carboniferous and an early Permian sandstone yielded zircon and rutile signatures compatible with recycling of Palaeozoic sediments north of southernmost Scotland, probably reflecting inversion tectonics. Recycling of Mesoproterozoic to Palaeozoic sediments is thus a prominent feature of the studied late Palaeozoic sandstones. Supplementary material: Electron microprobe data from rutile trace element analyses, additional rutile temperature plots and zircon LA-ICPMS U–Pb data are available at http://www.geolsoc.org.uk/SUP18617.