Dr Dave Schofield, British Geological Survey, Edinburgh
During the 1970s, the recognition of allochthonous terranes as discrete lithospheric fragments gave geologists a new tool kit to help describe the mosaic-like complexity of orogenic belts. Understanding that terranes could be dispersed and recombined accompanied realisation that strike-slip translation contributed significantly to orogenic development.
In applying this to understanding the, largely concealed, late Neoproterozoic and Lower Palaeozoic record of southern Britain, conflicts in nomenclature, scales of observation and focus of the geologist’s themselves has led to a confusing picture where terranes are essentially reduced to snapshots in time rather than lithospheric entities evolving in both time and space.
This talk takes a look at this problem and uses summaries of isotopic data to contrast Neoproterozoic rocks with their Cambrian cover successions in southern Britain and those in the Caledonian-Appalachian Orogen as a whole, and looks at when the component terranes may have been assembled and largely stabilised.
Earlier interpretations of the orogeny compare southern Britain with Avalon Peninsula in Newfoundland based on the similarity of their Cambrian shelfal sedimentary successions and cold water faunas, known as East and West Avalonia respectfully. However, isotopic studies of the Precambrian basement to southern Britain show that it more closely resembles that of other terranes that formed around the continental margin of West Gondwana, Meguma of Nova Scotia and Ganderia of Central Newfoundland and New Brunswick of the northern Appalachians.
Similarly, U-Pb zircon provenance studies of the overlying Cambrian cover successions show that North Wales and the Midland Platform of England most closely resemble Meguma while those of Anglesey (Monian Composite Terrane) and the Leinster-Lakesman Terrane most closely resemble Ganderia. While in the northern Appalachians these terranes largely travelled separately before their accretion in a piecemeal fashion onto the continental margin of Laurentia; in the UK they were juxtaposed during the Early Ordovician Monian Orogeny, after which southern Britain and Ireland probably travelled as a single terrane before arriving on Laurentia during the Silurian.
David undertook a PhD at Keele University in 1995 and has worked with the BGS in various roles since then. Currently he is Director, Energy Systems and Basin Analysis, having previously been Chief Geologist, Wales.
This lecture will be held as a Zoom meeting. Society members for whom we have email addresses will be sent an invitation a few days before the event. If you are a member but are not on our email list, or a non-member who would like to join the meeting, please email the society’s meetings secretary to request an invitation.