Tectonic significance of a supra-ophiolitic sedimentary cover succession, Unst, Shetland, Scottish Caledonides: insights from the U–Pb–Hf detrital zircon record

Abstract

The tectonic significance of the Muness Phyllite which overlies the Unst-Fetlar ophiolite in Shetland, Scottish Caledonides is poorly understood. U-Pb analyses of detrital zircons show that it was deposited after c. 469 Ma. Lower Palaeozoic grains have εHf values of -0.3 to +12.3 and were likely derived from the extension of the Midland Valley arc. Psammite clasts and the matrix of the Muness Phyllite contain Proterozoic and Archaean detrital zircons with age peaks of c. 1 Ga, 1.4 - 1.5 Ga, 1.6 - 1.7 Ga, 1.8 - 1.9 Ga and 2.7 Ga. These are consistent with ultimate derivation from NE Laurentia sources and were probably recycled from the Neoproterozoic East Mainland Succession that underlies the Mesozoic East Shetland Basin. The Muness Phyllite is interpreted to have been deposited soon after the Grampian I orogeny in a successor basin that overstepped, and received detritus from, the Midland Valley arc, the East Mainland Succession and the Unst-Fetlar ophiolite. It was then deformed and metamorphosed, probably at c. 450 Ma during the Grampian II orogenic event. The Muness Phyllite therefore provides a record of middle to late Ordovician tectonic events along the Scottish sector of the Laurentian margin following ophiolite obduction.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5324986

Zircon U–Pb–Hf snapshots on the crustal evolution of the Serbo-Macedonian massif: new insights from Ammouliani island (Northern Greece)

“…The 171 Yb, 173 Yb, 174 Yb, 175 Lu, 176 177 Hf, 178 Hf, 179 Hf, 180 Hf, 181 Ta and 182 W masses were measured in the first session (sample KP18-3), whereas in the second session (sample KP18-1) the 172 Yb mass was measured instead of 171 Yb owing to space problems between the Faraday cups and ion counters. The guidelines of Fisher et al (2014) were followed to calculate the mass bias corrected contribution of 176 Yb and 176 Lu on the 176 Hf ion beam signal and are described in more detail in Papapavlou et al (2021). The dated intragrain domains were analysed for Lu-Hf using a spot size of 65 μm, repetition rate of 7 Hz (sample KP18-1) or 15 Hz (sample KP18-3) and fluence of 9 J cm −2 using the Photon Machines laser instrument coupled to a Nu AttoM II multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS).…”