The Caledonides of the British Isles--reviewed. 1979. Geological Society of London. The Newry igneous complex, County Down

SUMMARY: New field and petrographic observations indicate that the ultramafic rocks and closely associated meladiorites at the northeast end of the complex are principally clinopyroxene-biotite-apatite (-plagioclase) cumulates from intermediate magmas. The meladiorites grade into more evolved oversaturated dioritic-monzonitic rocks, many of which may also be accumulative, and consequently the main intermediate and ultramafic body is thought to be part of a layered intrusion. New geochemical data for major and trace elements (including R.E.E.) and initial 87Sr/86Sr ratios show compositional similarities between some of the intermediate rocks and the younger granodiorites. The granodiorites are areally most abundant and probably constitute three contiguous plutons formed mainly by crystal fractionation at depth in intermediate magmas of Upper Mantle origin. The Newry igneous complex intruded and horn-felsed the folded Silurian greywackes and slates of the Longford-Down massif, and is thus com-parable with the Caledonian granitic intrusions of SW Scotland. It shows a marked NE-SW elonga-tion and is composed of probably three contigu-ous granodiorite plutons together with an earlier intrusion of intermediate and ultramafic rocks at its NE end (Fig. 1 and Richey & Thomas 1932, Reynolds 1934). The complex is cut by late Caledonian and Tertiary dykes and, at its south-west end, by the Slieve Gullion Tertiary complex, O'Connor (1975) having established a whole-rock Rb-Sr age of 399 _ 21 Ma (2 = 1.39 x i0-11 yr-a) for the granodiorites of this southwest area. Reynolds (1944) proposed an essentially non-magmatic 'transformist ' origin for all the