Sm-Nd garnet age for the Ordovician Borrowdale Volcanic Group, English Lake District
- 16 May 1983
- journal article
- Published by Geological Society of London in Journal of the Geological Society
- Vol. 140 (3) , 511-518
- https://doi.org/10.1144/gsjgs.140.3.0511
Abstract
Garnets separated from andesites and dacites of the calc-alkaline Borrowdale Volcanic Group are highly enriched in heavy rare earth elements (HREE) relative to their host rocks (D Gt Yb from 9 in andesite to 37 in dacite). Sm/Nd ratios and D Gt LREE show a wide range, probably resulting from small quantities of an REE-rich impurity in the separates. The four garnet-host rock pairs analysed yield Sm-Nd ages identical within analytical error of a weighted mean of 457 ± 4 Ma. The Borrowdale. Group overlies upper Llanvirn sediments and is unconformably overlain by mid-Caradoc. The age of 457 Ma is considered to be the best estimate available for the age of the Llandeilo, as the samples analysed are from the lower part of the Group. The age suggests that a Lower Palaeozoic timescale intermediate between those of Gale et al . (1979) and McKerrow et al . (1980) might be the most appropriate.Keywords
This publication has 25 references indexed in Scilit:
- Influence of rock crystallisation history upon subsequent lanthanide mobility during hydrothermal alteration of basaltsPublished by Elsevier ,2003
- Sm–Nd dating and cooling history of Scourian granulites, SutherlandNature, 1982
- Discussion of a paper by McKerrow, Lambert and Chamberlain on the Ordovician, Silurian and Devonian time scalesEarth and Planetary Science Letters, 1980
- Nd and Sr isotopic study of the Bay of Islands Ophiolite Complex and the evolution of the source of midocean ridge basaltsJournal of Geophysical Research, 1979
- A Rb-Sr whole rock isochron for the Stockdale Rhyolite of the English Lake District and a revised mid-Palaeozoic time-scaleJournal of the Geological Society, 1979
- Sm—Nd systematics of Lewisian gneisses: implications for the origin of granulitesNature, 1979
- Distribution of trace elements between garnet megacrysts and host volcanic liquids of kimberlitic to rhyolitic compositionGeochimica et Cosmochimica Acta, 1978
- A review of experimental studies of crystal/liquid trace element partitioningGeochimica et Cosmochimica Acta, 1978
- Petrotectonic environments of the Girvan-Ballantrae lavas from rare-earth element distributionsScottish Journal of Geology, 1977
- The genetic significance of almandine-pyrope phenocrysts in the calc-alkaline Borrowdale Volcanic Group, Northern EnglandContributions to Mineralogy and Petrology, 1972