Geochemistry of the Tertiary volcanism of Northern Ireland

doi:10.1016/0009-2541(95)00137-9

Chemical Geology

Volume 129, Issues 1–2, 14 June 1996, Pages 15-38

https://doi.org/10.1016/0009-2541(95)00137-9 Get rights and content

Abstract

The Antrim Plateau (Northern Ireland) forms the southwestern part of the British Tertiary Igneous Province and is dominated by basaltic lavas. Previous work divided the province into three stratigraphic formations, viz. the Lower, Middle and Upper Formations, with the Middle Formation having a basaltic member known as the Causeway Member. New chemical and SrNd isotopic data covering the spectrum of lava types are presented. Three distinct geochemical types are recognised: (1) basalts of the Lower Formation and most of those from the Upper Formation are LREE-enriched but have characteristic convex-up REE patterns with a maximum around Nd; (2) some of the Upper Formation basalts and the majority of the Causeway Member basalts are LREE-enriched with no convex shape in their REE pattern; and (3) some of the Causeway Member basalts are LREE-depleted and similar to N-MORB. Isotopic compositions of Sr and Nd show considerable variation throughout the three formations with ε_Sr(t) = − 22 to + 107 and ε_Nd(t) = − 11 to + 8.5. The exceptionally wide ranges of isotopic compositions are believed to have been produced by assimilation of a crustal (mainly Dalradian derived) component. The REE patterns indicate that most of the basalts were derived from a LREE-depleted mantle and with the exception of the Causeway Member, most have convex-up REE patterns. These are interpreted as being due to residual garnet in the mantle source, which indicates melting at depths in excess of 80 km. This suggests that at the start of Tertiary volcanism, the melt regime was controlled by a thick lithosphere which thinned with time such that the Causeway Tholeiites were produced at shallower levels. The return to the convex-up patterns of the Upper Formation means that simple models of lithospheric stretching and rifting are not able to explain the Antrim situation.

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Research paperGeochemistry of the Tertiary volcanism of Northern Ireland

Abstract

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Earth Planet. Sci. Left.

Earth Planet. Sci. Left.

Earth Planet. Sci. Left.

Geochim. Cosmochim. Acta

Chem. Geol

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Chem. Geol.

Earth Planet. Sci. Lett.

How deep do common basaltic magmas form and differentiate?

J. Geophys. Res.

The role of lithospheric mantle in continental flood volcanism: thermal and geochemical constraints

J. Geophys. Res.

Tertiary and post-Tertiary geology of Mull, Loch Aline and Oban

Mem. Geol. Surv. G.B.

Determination of rare earth elements in sixteen silicate reference samples by ICP-MS using a Tm addition and an ion-exchange chromatography procedure

Geostand. Newsl.

Selectively contaminated magmas of the Tertiary East Greenland macrodike complex

Contrib. Mineral. Petrol.

Implications of mantle plumes for the evolution of flood basalts

Earth Planet. Sci. Lett.

Isotopic evidence for lithospheric thinning during extension: Southeastern Great Basin

Geology

A precise U-Ph zircon age for the Inishtrahull syenitic gneiss, County Donegal, Ireland

J. Geol. Soc. London

Combined SmNd and RbSr isotope systematics in the Donegal granitoids and their petrogenetic implications

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Research paper
Geochemistry of the Tertiary volcanism of Northern Ireland