NW UK continental margin : chronology and isotope geochemistry

Chambers, Lynne; Darbyshire, Fiona; Noble, Stephen; Ritchie, Derek. 2005 NW UK continental margin : chronology and isotope geochemistry. Nottingham, UK, British Geological Survey, 161pp. (CR/05/095N) (Unpublished)

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Until recently, a significant proportion of the crystalline basement from the NW UK continental shelf was virtually terra incognita in comparison with similar rocks on the mainland. A significant increase in the geological understanding of this region’s crystalline rocks is provided by new data from 42 boreholes, some of which were only drilled in 2001. The samples are from a ~550 km long transect of the UK continental shelf, extending from ~50 km west of Shetland in the northeast to Stanton High, south of the Outer Hebrides and westward to include Rockall High. Petrography and geochemistry show the main lithologies are amphibolite to granulite facies amphibolites and gneisses, and include classic Archaean TTG’s, metabasic rocks, granite (s.s), and granitic pegmatites. A long history of crustal growth is indicated by U-Pb zircon ages and Nd model ages. Archaean gneisses that developed in two main episodes dominate much of the study area. The older gneisses (c. 2.8 Ga) represent new continental crust while genesis of the later gneisses (c. 2.74-2.70 Ga) involved crustal recycling. Both groups are very similar to onshore Lewisian gneisses. Important areas of known Proterozoic crust were also characterized, confirming the results of previous studies. Geochemistry and Nd isotope systematics of Stanton High documents extensive Archaean crust re-working in the Proterozoic, as well as addition of new continental crust. Stanton High U-Pb zircon ages (1799-1791.5 Ma) are similar to the Rhinns terrane (c. 1800 Ma). Westward, Rockall High borehole samples yield a 1744.9 Ma U-Pb age, distinct from Stanton High – Rhinns rocks. Nd data indicate addition of mantle-derived juvenile crust, as previously noted elsewhere on Rockall High. An isolated granulite facies metabasic rock on the NE portion of the Hebrides shelf was dated at 1633.5 Ma, also representing a new addition of crust. The new data provide important constraints for regional correlations and palaeotectonic reconstructions. The Archaean rocks are almost certainly related to the Lewisian: given current models, they probably also correlate to the Nagssugtoquidian in Greenland, while the Rockall and Stanton Highs, together with the Rhinns terrane, have affinities to the Ketilidian of Greenland and the Svecofennian of Scandinavia.

Item Type: Publication - Report
Programmes: BGS Programmes > NERC Isotope Geoscience Laboratory
Funders/Sponsors: Rockall Consortium
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externally peer-reviewed. This report made open by Phil Richards May 2015
Date made live: 18 May 2015 13:01 +0 (UTC)

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