Abstract

Andrew C. Kerr & Ray W. Kent write: In a recent paper, Bell & Jolley (1997) used palynological data to propose that the Mull Tertiary lava succession and the upper Antrim lavas are significantly younger (by 2–4 Ma) than the Skye Main Lava Series. In support of this proposal, they correlated the StaVa magma sub-type (found at the base of the Mull lava pile) with the two Preshal More-type flows on Skye, and suggested that these two magma types are compositionally similar. We contend that neither of these suggestions is correct, and discuss data that are at variance with the conclusions reached by Bell & Jolley.

Eruption of the Mull lava succession was believed by Bell & Jolley to have started at c. 55 Ma, about 4 Ma after the commencement of igneous activity on Skye. The suggestion of a 55 Ma age for Mull basalts ignores four 40Ar/39Ar incremental heating ages (weighted mean=60.0±0.5 Ma, 1σ error) obtained by Mussett (1986) on lavas from the lower part of the Mull Plateau Group. Bell & Jolley believed these ages to be unreliable, yet they satisfy all of the acceptance criteria of Lanphere & Dalrymple (1978), i.e., they can be considered as reliable estimates of the true crystallization ages of these basalts. Furthermore, Mussett’s (1986) 40Ar/39Ar data for the Mull lavas are consistent with Rb–Sr and 40Ar/39Ar ages obtained for Mull granites (58.1±1.6 Ma to 56.5±1.0 Ma, Walsh et al. 1979; Mussett 1986). All of these radiometric ages

First Page Preview

First page PDF preview
You do not currently have access to this article.