Sr isotope data for the Tertiary lavas of Northern Ireland: evidence for open system petrogenesis

Abstract

The lavas of NE Ireland represent the largest remnant of the British and Irish Tertiary Igneous Province. In this paper we present new Sr isotope data which, by virtue of extreme variation, provide evidence of extensive open system behaviour in the petrogenesis of these flood basalts. To some extent the initial 87 Sr/ 86 Sr ratios ( 87 Sr/ 86 Sr (60Ma) = 0.703–0.715) record the effects of late-stage hydrothermal processes. However, leaching experiments allow primary magmatic signatures to be inferred with confidence. Coherent increases in initial 87 Sr/ 86 Sr ratio with differentiation indices and incompatible trace element ratios imply a role for crustal contamination. Very significant differences in the style of crustal interaction are recorded by discrete units within the basalt pile. Further, there are also marked contrasts with Tertiary basalts elsewhere in the United Kingdom. In both cases such variations appear to respond to changes in the basement geology reflecting the important control of crustal wall-rocks on the geochemistry of these basalts.

Mobility during the neolithic and bronze age in northern ireland explored using strontium isotope analysis of cremated human bone

“…in all samples, higher than the 20–30% concentration observed in unburned archaeological human bone (Grupe, ; Mahanti and Burnes, ) but this is to be expected since no organic matter remains and large amounts of carbonates and water have been lost during calcination. The highest concentration is recorded in sample BM1b found in a basalt formation which follows the observation that, basalts are amongst the geological units with the highest strontium concentrations compared to granites and other units (Meighan et al, ; O'Connor, ; Wallace et al, ).…”

“…Palaeozoic lithologies (545‐248 Ma) predominate, especially Carboniferous sedimentary rocks (350 − 290 Ma); there are several large granitic bodies and, in Co. Antrim in the northeast, an extensive outcrop of mantle‐derived Tertiary (60 Ma) basaltic lavas. Consequently, and relevant to this research, there is a large range of present‐day strontium isotope compositions, from below 0.7040 in some Antrim basalts to over 1.15 in certain Mourne Mountains granites (Wallace et al, ; Meighan et al, ). The subsurface is composed, among other things, of Holocene peat bogs and glacial till originating mostly from the last deglaciation around 14 kya.…”

Migration and Viking Dublin: paleomobility and paleodiet through isotopic analyses

“…These rocks, particularly in the north, are of substantial age and likely have quite high radiogenic strontium isotope ratios. Tertiary basalts in northeast Ireland, on the other hand, are relatively young and low in rubidium and exhibit radiogenic strontium isotope values between 87 Sr/ 86 Sr ¼ 0.704 and 87 Sr/ 86 Sr ¼ 0.707 (O'Connor, 1988;Wallace et al, 1994). Limestone deposits are found in limited areas, largely in the west and southwest of Ireland; these marine sediments will have radiogenic strontium isotope values closer to modern seawater, in which 87 Sr/ 86 Sr ¼ 0.709 (Burke et al, 1982;McArthur et al, 2001;Veizer, 1989).…”

“…a). Published radiogenic strontium isotope ( 87 Sr/ 86 Sr) values from bedrock and water sources in Northern Europe (Aberg et al, 1998;Budd et al, 2000;Burke et al, 1982;Darbyshire and Sheperd, 1985;Dickin, 1997;Gallett et al, 1998;McArthur et al, 2001;Negrel et al, 2003;O'Connor, 1988;Voerkelius et al, 2010;Wallace et al, 1994;Wilson et al, 1977). b).…”

Discussion on a latest Cretaceous hotspot and the southeasterly tilt of Britain

“…However, it seems more than likely that the whole of the Southern Uplands and the Midland Valley of Scotland would have had a cover of Chalk. As far as Northern Ireland is concerned, the fact that the Upper Basalt Formation is most extensively preserved in the northernmost region of the province (Wallace et al 1994, fig.1) suggests that the zero contour should run near the coast there. If the contour is extrapolated thence into the western part of Ireland, it suggests that much of Ireland has lost significant cover, and it is to be noted that recent palaeogeographic studies (e.g.…”