Mapping a hidden terrane boundary in the mantle lithosphere with lamprophyres.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 30217975.
- Also identified by DOI 10.1038/s41467-018-06253-7 and PMC identifier 6138702.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Lamprophyres represent hydrous alkaline mantle melts that are a unique source of information about the composition of continental lithosphere. Throughout southwest Britain, post-Variscan lamprophyres are (ultra)potassic with strong incompatible element enrichments. Here we show that they form two distinct groups in terms of their Sr and Nd isotopic compositions, occurring on either side of a postulated, hitherto unrecognized terrane boundary. Lamprophyres emplaced north of the boundary fall on the mantle array with ε<sub>Nd</sub> -1 to +1.6. Those south of the boundary are enriched in radiogenic Sr, have initial ε<sub>Nd</sub> values of -0.3 to -3.5, and are isotopically indistinguishable from similar-aged lamprophyres in Armorican massifs in Europe. We conclude that an Armorican terrane was juxtaposed against Avalonia well before the closure of the Variscan oceans and the formation of Pangea. The giant Cornubian Tin-Tungsten Ore Province and associated batholith can be accounted for by the fertility of Armorican lower crust and mantle lithosphere.