Irish Geological Association Members’ Night
13th December @ 6:30 PM GMT
Rooftop Bar, Hyde Dublin, 9 Lemon Street, Dublin 2
Google Maps Link: https://maps.app.goo.gl/49X8RW8tMZZEj2V36
The lecture below will be show to those present in person at the member’s night via a laptop from 7pm. Platters will be served, and an informal quiz will be the entertainment for the night!
IGA Virtual Lecture via Zoom
Investigating Archaean Terrane Boundaries in Scotland
13th December @ 7:00 PM GMT
Dr Eszter Badenszki (iCRAG, UCD)
Absract: Establishing terrain boundaries within Archaean lithospheric units is challenging because, like those that form the Lewisian Complex in Scotland, they commonly comprise rather uniform-looking gneisses. Identifying terrane boundaries has, therefore, leant heavily on various isotopic dating techniques and geochemical tracer methods.
The geological evolution of the Lewisian Complex of northwest Scotland is much debated; there are conflicting models for its formation and the number, character, and location of terrane boundaries within it. Originally regarded as a continuous unit, it was subsequently subdivided into multiple terranes based on in situ U–Pb zircon geochronology (Friend and Kinny 1995; Kinny et al. 2005). A radically different two-plate model has also been suggested (Park 2005, 2022), primarily based on correlating structural and metamorphic features with major tectonic units in Greenland.
In an attempt to reconcile the conflicting models for the Lewisian Complex, we have paired field observations with feldspar Pb isotopic compositions in order to build a geochemical map for the complex. Feldspars, both K-feldspar and plagioclase, are abundant rock-forming minerals with low U/Pb and Th/Pb ratios and, hence, have time-invariant Pb isotope compositions. We systematically collected nearly 160 onshore samples to cover all the major outcropping regions. Also, we included 15 drilled cores from offshore sites of the Hebridean Shelf to test previously established terrain models. Our results are most consistent with a two- plate model, where the Assynt, Gruinard, and East Barra regions likely correlate with the North Atlantic Craton of Greenland. The rest of the onshore Lewisian Complex feldspar Pb isotopic data, together with the southernmost offshore borehole data, strongly overlap with compositions obtained from the Nagssugtoqidian terrane in southeast Greenland. The remaining offshore samples, situated north of the Lewisian outcrop, have a very different and distinct Pb isotopic signature and may correlate to a third terrane, likely the Rae Craton of Greenland.
Friend C.R.L. & Kinny, P.D. 1995. Geology, 23, 1027-1030.
Kinny, P.D., Friend, C.R.L. & Love, G.J. 2005. Journal of the Geological Society, London, 162, 175-186.
Park, R.G. 2005. Scottish Journal of Geology, 41, 105-118. Park, R.G. 2022. Scottish Journal of Geology, 58, sjg2021-2020.
Eszter earned her geology diploma in Budapest, Hungary, in 2006 and finished her PhD in 2014 at University College Dublin (UCD). The projects she worked on focused on deep crustal xenoliths. For her PhD, she studied the origin and evolution of the deep crust of the Scottish Midland Valley using geochronology and geochemical methods, such as thermobarometry, whole-rock chemistry, and Sm–Nd and Lu–Hf isotope geochemistry. Eszter continued her research as a post-doctoral researcher with iCRAG at UCD, focusing on Irish deep crustal xenoliths. During these years, she managed the laser ablation isotope and petrographic imaging facilities at UCD undertaking in situ Lu–Hf zircon analyses, trace element analyses and geochemical mapping of oxide and silicate minerals, especially Pb isotopic analyses of feldspars on which several sedimentary provenance projects relied. In recent years she has focused on Pb-isotopic mapping of the Lewisian Complex, supported by iCRAG in collaboration with the Cambridge Arctic Shelf Programme (CASP, UK).
A Zoom link will be sent on the day to those who have registered.