Wed 28th March @ noon, Rm 312.222

Abstract:

Assembly of Rodinia culminated in development of the collisional Grenville-Sveconorwegian orogen at 1.2-1.0 Ga. The tectonic significance of early Neoproterozoic (980-920 Ma) tectonothermal events recorded in the North Atlantic borderlands of Ellesmere Island, East Greenland, Norway and Svalbard is less well understood. This is partly because most rock units were reworked at amphibolite facies during the Lower Palaeozoic Caledonian orogeny, and also because there is controversy over the relative positions of Laurentia and Baltica in Rodinia reconstructions. U-Pb zircon dating of metasedimentary rocks and a range of mafic, intermediate and felsic meta-igneous rocks from the Shetland Islands and mainland northern Scotland provides evidence for a hitherto unrecognised tectonothermal event at 970-930 Ma. Geochemical and isotopic data are consistent with magma generation in a convergent plate margin setting. The identification of subduction-related magmatism at least as far south as the Scottish sector of the eastern Laurentian margin favours a southerly location of western Baltica opposite Rockall Bank. This enables the Scottish margin of east Laurentia to be located relatively close to the periphery of Rodinia, and early Neoproterozoic magmatism and orogenesis to be related to development of an exterior accretionary orogen following supercontinent assembly. Similar-aged calc-alkaline igneous suites have been identified by other workers in Ellesmere Island, Svalbard, and within Laurentia-derived allochthons of northern Norway, and together with the Scottish occurrences these comprise the recently-defined Valhalla accretionary orogen of northeast Laurentia.

Short bio:

Rob did his PhD at the University of Keele, UK, and has since held academic positions at Oxford Brookes University and most recently the University of Portsmouth where he is Professor of Geology. His research is centred around Neoproterozoic and Lower Palaeozoic tectonics in the North Atlantic region.