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The Lagavulin exploration well 217/15-1Z penetrated a c . 2.6 km thick volcanic sequence dominated by extrusive basaltic rocks spanning the Paleocene–Eocene boundary in the NE Faroe–Shetland Basin. The well comprises one of the thickest drilled sequences through the North Atlantic Igneous Province. Integrated analysis of drill cuttings and wireline-log data reveals key volcanic lithofacies: (1) tabular lava flows; (2) compound lava flows; (3) hyaloclastite; (4) volcaniclastic rocks. The volcanic facies reveal two major sub-aqueous to subaerial sequences consistent with lava delta progradation. These sequences are separated by a volcanic hiatus represented by extensive reddened soils, which preceded the re-submergence of the area. Emergence followed by submergence of the first lava delta is interpreted to record an intra-T40 transient uplift event near the Paleocene–Eocene boundary. Basalts from the lower c . 1.3 km have low TiO 2 ( 85–91 ). The hiatus correlates precisely with a change to high-TiO 2 (2.5–3.2 wt%), high-Zr/Y (>4) compositions, which dominate the upper sequence. The associated change in lava geochemistry, transient uplift and volcanic hiatus appears consistent with a transient pulse of hot buoyant plume material passing beneath the area. Supplementary material: All raw geochemical data and supplementary analyses are available at http://www.geolsoc.org.uk/SUP18888.

Age-corrected Pb, Sr and Nd isotope ratios early Aptian basalt from four widely separated sites on the Ontong Java Plateau that were sampled during Ocean Drilling Program Leg 192 cluster within the small range reported for three earlier drill sites, for outcrops in the Solomon Islands, and for the Nauru and East Mariana basins. Hf isotope ratios also display only a small spread of values. A vitric tuff with eNd(t) = +4.5 that lies immediately above basement at Site 1183 represents the only probable example from Leg 192 of the Singgalo magma type, flows of which comprise the upper 46-750 m of sections in the Solomon Islands and at Leg 130 Site 807 on the northern flank of the plateau. All of the Leg 192 lavas, including the high-MgO (8-10 wt%) Kroenke-type basalts found at Sites 1185 and 1187, have eNd(t) between +5.8 and +6.5. They are isotopically indistinguishable from the abundant Kwaimbaita basalt type in the Solomon Islands, and at previous plateau, Nauru Basin and East Mariana Basin drill sites. The little-fractionated Kroenke-type flows thus indicate that the uniform isotopic signature of the more evolved Kwaimbaita-type basalt (with 5-8 wt% MgO) is not simply a result of homogenization of isotopically variable magmas in extensive magma chambers, but instead must reflect the signature of an inherently rather homogeneous (relative to the scale of melting) mantle source. In the context of a plume-head model, the Kwaimbaita-type magmas previously have been inferred to represent mantle derived largely from the plume source region. Our isotopic modelling suggests that such mantle could correspond to originally primitive mantle that experienced a rather minor fractionation event (e.g. a small amount of partial melting) approximately 3 Ga or earlier, and subsequently evolved in nearly closed-system fashion until being tapped by plateau magmatism in the early Aptian. These results are consistent with current models of a compositionally distinct lower mantle and a plume-head origin for the plateau. However, several other key aspects of the plateau are not easily explained by the plume-head model. The plateau also poses significant challenges for asteroid impact Icelandic-type and plate separation (perisphere) models. At present, no simple model appears to account satisfactorily for all of the observed first-order features of the Ontong Java Plateau. © The Geological Society of London 2004.

SUMMARY The Eycott Volcanic Group, at the northern margin of the Lower Palaeozoic inlier in the Lake District, is the smaller of two substantial middle Ordovician (Caradoc) subduction-related volcanic successions that stratigraphically separate marine sedimentary successions of the Skiddaw Group and Windermere Supergroup. Tabular lavas and subordinate sills, in a sequence up to 2400 m thick, mainly comprise porphyritic basalt, basaltic andesite, andesite and dacite, and are locally interbedded with thin units of volcaniclastic sandstone and pyroclastic rocks; these are overlain by 800 m of acid andesitic pyroclastic rocks. The distribution and form of the lava/sill fades association are consistent with emplacement as a lava plateau sequence, remarkably similar to the Birker Fell Formation, the lower part of the Borrowdale Volcanic Group in the central Lake District. The Eycott Volcanic Group rocks are geochemically coherent with characteristics transitional between medium-K, continental-margin tholeiitic, and calc-alkaline andesite suites. Rocks within the suite can be linked by fractionation of an assemblage of plagioclase, pyroxene, Fe–Ti oxide and apatite. A prominent compositional gap between about 58 and 65% SiO 2 is attributed to the rapid precipitation and segregation of Fe–Ti oxide. Incompatible element concentrations in the mafic members suggest that magmas were derived possibly from a subcontinental lithosphere source, similar to that of the Borrowdale Volcanic Group. The geochemical differences between these two suites arose through the incorporation of different amounts of the subduction component and different fractionation histories.

The central part of the 65 000 km 2 lava plateau in East Greenland between Kangerlussuaq and Scoresby Sund has been investigated by multi-model photogrammetry and profile sampling, and a three-dimensional framework for the lava plateau has been established. Post-volcanic movements have divided the region into several structural blocks with dips varying from 1–2° N-NE in the inland areas to 12°SE at the coast. A major N-S-trending fracture zone may reflect an underlying Caledonian structure. Early volcanic and sedimentary rocks are overlain by widespread plateau basalts, locally with an angular unconformity of 8°. The basalt stratigraphy established in the Scoresby Sund area has been extended over most of the region. The plateau basalts were erupted over a zone more than 150 km wide, from the present coast and inland. The succession attains a vertical thickness of more than 5.5 km in the central coastal areas and thins inland to 2–3 km. A differential sagging of the coastal areas by at least 2.3 km took place during the emplacement of the lavas, accelerating with time. The features suggest increasing focusing of the magmatic production into a developing rift zone close to the present coast.

Synopsis Volcanic rocks exposed at Monksgrave which were formerly assigned to the Lower Devonian Ochil Volcanic Formation are now assigned to the Lower Carboniferous Clyde Plateau volcanic rocks. The new correlation is made on the basis of chemical and lithological similarities of the Monksgrave rocks to Lower Carboniferous volcanic rocks in the neighbouring Cleish Hills.

SUM M A R Y: Well 163/6-1 A, located in the northern part of the Rockall Trough, proved the presence of a thick sequence of extrusive igneous rocks below Upper Palaeocene sediments. K-Ar age dating suggests that the lavas were extruded at approximately 55 Ma. The lava sequence comprises three distinct lithologies. The upper part of the pile consists of olivine tholeiites that show alkalic and picritic tendencies and have a distinct within-plate composition. These are underlain by another group of olivine tholeiites that are much closer in composition to normal mid-ocean ridge basalt (N-type MORB). The Sr and Pb isotopic compositions of the basalts suggests possible contamination by continental crustal material. The basalts are underlain by a sequence of cordierite-phyric dacites of remarkably homogeneous composition. Their highly aluminous nature, high Ni and er contents and their Sr and Pb isotopic compositions indicate that they are not differentiates of a basaltic parent magma, and are considered to have originated by melting of argillaceous and, possibly, arenaceous rocks at depth. Organic-rich black shale lithologies may have been involved.

Interbedded with the clastic fluvial sediments of the Munster Basin, the Lough Guitane Volcanic Complex represents a rare volcanic episode in the Upper Devonian of SW Ireland. From three distinctly separate volcanic centres, an exclusively rhyolitic suite of thick lava flows and tuffs were erupted. The largest of the centres possessed a system of contemporaneous faults producing a subcircular depressed area, itself enclosed within a graben 1.5 km across. These faults lead to rapid thickness variations in many volcanic units, and a pooled lava flow reaches a thickness of 300 m. The site of a major elongate vent lies along one such fault, and rapid erosion of its poorly lithified walls generated coarse sandstone boulder agglomerates and is related to the absence throughout the complex of normal air-fall tuffs unmixed with terrigenous sand. The containment of the bulk of the volcanics by contemporaneous faults, and subsequent rapid burial by terrigenous sediments has led to preservation of the volcanic succession virtually intact.

I. Introduction. The Lower Limestone Series in the area about to be described lie to the north of a line drawn from Drumclog, east to Lesmahagow, and thence north-east by Kilncadzow to the Cobbinshaw Reservoir on the confines of Lanarkshire and Midlothian. They form a lip or edge of the basin which has the great Coal Measure Series of Lanarkshire in the centre, and they are bounded on the west and south by the volcanic plateau of Eaglesham and Strathavon, which separates them from the Ayrshire basin, and on the south and east by rocks of Lower Old Red Sandstone and Calciferous Sandstone age. Though now separated from the Lower Carboniferous Limestone area of Renfrewshire and Ayrshire by the volcanic plateau of lavas, at one time the two areas must have been more or less continuous, as can be shown by the occurrence of such outliers of the limestone as we find at Ryeland and Drumclog resting directly upon the lavas. The former continuity of the two areas is also clearly brought out by the identity of the limestone series on each side of the volcanic ridge, as we hope to be able to show that such well-marked horizons as the Dockra or Blackbyre Limestone, the Blackhall Limestone, the Calderwood Cement or top Hosie Limestone, the Slingstone Limestone or top marine band, all with characteristic faunal associations, can be traced over many hundreds of square miles from the neighbourhood of Dalry on the west to the This 250-word extract was created in the absence of an abstract

In Mr. E. M. Patterson9s “Preliminary Note on the Tertiary Lava Succession in North Antrim” ( Abs. Proc. Geol. Soc. No. 1461, 28 March, 1950, p. 91) he claims that there are, in North Antrim, two interbasaltic horizons, characterized by the presence of laterite and separated by a Middle Lava Series consisting of tholeiitic basalts. The writer of the present note spent much time during the war in examining the Antrim laterites, and has prepared an account of them which is about to go to press. This new conception of Mr. Patterson9s is therefore a matter of particular interest to him. The development of a laterite horizon, as distinct from the frequent but less-prolonged minor interbasaltic periods whose existence is well known, implies a major time-break in the volcanic sequence. For this and other reasons stated below the writer considered that Mr. Patterson9s claim required careful examination. The Antrim lava plateau is built up of a succession of sub-aerial flows. Weathering of individual flows, marking, in most cases, minor interbasaltic periods, may be indicated by the presence of thin layers of red “bole”, by kaolinization of basalt, forming lithomarge, or by kaolinization followed by lateritization, i.e. by the formation of aluminous and ferruginous laterite (bauxite and iron ore). The existence of one major interbasaltic horizon, with deposits subsequently recognized to be lateritic in origin, has been known for at least 150 years. It was mapped during the primary geological survey of Ireland. The bauxite and iron ore were mined for many