Conference Contribution Details
Mandatory Fields
McKenna, C., Gamble, J., Renne, P., Ellam, R., Fitton, G, Lyle, P.;
Integration of the Intrusive and Extrusive Cycles of Palaeogene Igneous activity in NE Ireland
Prague, Czech Republic
Invited Oral Presentation
Optional Fields

We compare trace element and isotopic (Sr, Nd, and Pb) geochemical data from the mafic intrusive complex of Slieve Gullion with new data from the thick sills (up to 100 m) at Portrush, Carrickarede and Fair Head in N Antrim and make comparisons to the Antrim Lava Group (ALG) flood basalts.

Slieve Gullion rocks (56.5±1.3 Ma) are characterised by flat ~10x chondritic HREE with slight +ve Eu-anomalies and LREE enrichment ((La/Pr)CN = ~2.5). Portrush sill rocks (54.9±0.6 Ma) show similar flat HREE patterns,  +ve Eu anomalies and faint LREE enrichment ((La/Pr)CN = >1). By way of contrast Carrickarede and Fair Head (60.2±0.3 Ma) rocks show convex upward REE patterns, with maximum REE enrichment at Nd ((La/Pr)CN < 1, (Nd/Lu)CN ~ 4). Multielement plots of incompatible elements for Slieve Gullion and Portrush rocks display similar flat patterns for HREE and HFSE, with distinctive +ve spikes at Pb, Sr and Rb and ¿ve Nb anomalies, that strongly resemble subduction modified melts or continental crust. The Fair Head rocks show distinctive, smooth upwardly convex patterns.

The Lower Basalts (~60-62 Ma) of the ALG show similar convex upwards REE patterns as the Fair Head and Carrickarede rocks, whereas many of the younger Upper Basalts (~59-57 Ma) resemble the younger intrusions at Portrush and Slieve Gullion, but with flat or LREE depleted REE patterns.

A key to understanding the evolution of the N.E. Irish sector of the  North Atlantic Igneous Province is explaining such differences in temporally related rocks, which cannot be rationalised solely by partial melting of a similar source. We suggest that the LREE enrichment and Pb, Sr, Rb spikes so distinctive of the Slieve Gullion magmas, and also hinted at in Portrush, might derive from a lithospheric mantle component, as the melting regime penetrates into lithospheric mantle as extension developed across the Province.

SFR Research Frontiers