A comparison of the Skiddaw and Manx groups (English Lake District and Isle of Man) using neodymium isotopes

Abstract

SUMMARY Nd-isotope analyses of greywackes from the Skiddaw Group give an εNd range of −9.3 to −4.1, broadly compatible with suggestions of a provenance within an inactive and dissected, continental-margin volcanic arc. There is no clear temporal trend but the youngest greywackes have the lowest εNd values, perhaps suggesting an increase in the proportion of an older continental component through time as the arc was eroded. Two stratigraphical units were also sampled from the Manx Group, the likely lateral equivalent of the Skiddaw Group on the Isle of Man. Of these, the Lonan Flags gave εNd values of −6.0 and −5.1, within the upper part of the Skiddaw Group range. However, a sample from the slightly younger Maughold Banded Group has εNd = +2.1, indicative of a large influx of juvenile volcaniclastic detritus. This influx appears to have occurred earlier (mid-Arenig) in the Manx Group than in the Skiddaw Group where the first volcaniclastic interbeds are seen in the (Llanvirn) Tarn Moor Formation.