A COMPARISON OF THE SKIDDAW AND MANX GROUPS (ENGLISH LAKE DISTRICT AND ISLE-OF-MAN) USING NEODYMIUM ISOTOPES

Nd-isotope analyses of greywackes from the Skiddaw Group give an epsil on Nd range of -9.3 to -4.1, broadly compatible with suggestions of a provenance within an inactive and dissected, continental-margin volcan ic arc. There is no clear temporal trend but the youngest greywackes h ave the lowest epsilon Nd values, perhaps suggesting an increase in th e 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 epsilon Nd values of -6.0 and -5.1, within the upper part of the Skiddaw Group range. However, a sam ple from the slightly younger Maughold Banded Group has epsilon Nd = 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 interb eds are seen in the (Llanvirn) Tarn Moor Formation.