History of Tertiary igneous activity in the N Atlantic borderlands

Abstract

S U M M A RY: Stretching and thinning of the Laurasian continental lithosphere, which had proceeded intermittently from late Palaeozoic through the Mesozoic, reached a climax in early Tertiary times with copious generation of basalt magma, invasion of the attenuated crust as dyke swarms and surface eruption, principally by fissure volcanism. Continued basin subsidence allowed basaltic lavas, erupted at near sea-level, to accumulate to thicknesses which in places (e.g. W Greenland, E Greenland, Faeroes) attained several kilometres. In some zones dyke-swarm injection and crustal attenuation led to sea floor spreading and generation of ocean crust. Fissure swarms not infrequently changed position so that there could be one or more 'unsuccessful' rifting events prior to establishment of a 'successful' spreading axis.While some uncertainty still exists regarding the precise timing of the onset of magmatism in the various zones of failure, the bulk occurred between 60 and 50 Ma. Across the British Isles basalt magmatism occurred early (ca. 60-59 Ma) whereas the great volumes of the E Greenland basalts appear to have erupted rapidly over the interval 54--52 Ma. The onset of magmatism in the Faeroes may have preceded that in E Greenland and possibly that of W Greenland-Baftin Island.Major sill swarms developed, commonly within the Mesozoic sedimentary strata. At favoured channels for magma ascent, commonly controlled by major faults, longer-lived central-vent volcanoes developed. Slow cooling of large magma bodies at such foci produced mafic and ultramafic cumulates; production of salic magmas was mainly confined to these central complexes, the majority of which are located close to the E Greenland coast between ca. 66 ~ and 74~ and a N-S zone through the British Isles from ca. 58~176 Although the salic magmas were predominantly silicic (rhyolitic), feldspathoidal (phonolitic) magmas were important in some of the E Greenland centres. Generation of salic magmas was generally late with respect to the main phases of basalt eruption in the various sectors of activity. However, notable sequences of peraluminous silicic lavas may have preceded basaltic eruption in the Rockall Trough and Voring Plateau areas. It is probable that magmatic activity in some of the sectors that had experienced the most intense early-phase volcanism persisted, on a small-scale, long after the sea floor spreading had been initiated and activity on the passive margins of both W and E Greenland may not have finally terminated until ca. 30 Ma.The total compositional range of early Tertiary magmas associated with the N Atlantic marginal regions was extensive. Whereas tholeiites, varying from FeTi-rich to N-type MORB, were erupted in greatest volume, compositions varied from picrites, through tholeiites to ferro-basalts, icelandites, dacites and rhyolites. More alkalic mafic magmas included alkali olivine-basalt (and its differentiated products), nephelinites, lamprophyres and melilitites, with some associated carbonatites. Salic magmas ranged widely from...

The onset of the North Atlantic Igneous Province in a rifting perspective

“…Early Eocene magmatism in NE Greenland and at the Vøring margin had a close spatial relationship (Viereck et al 1988;Upton et al 1995) and recent studies reveal a continuous Early Eocene igneous complex that directly linked these two regions together in the early stages of sea-floor spreading (Olesen et al 2007). The igneous activities (volume and rock types) associated with these centres resemble those found in some places in the Rockall Trough (Upton, 1988) and on the NW British Isles (Viereck et al 1988 and references therein). Volumes of the Paleocene to Early Eocene volcanism decreased from the central Vøring margin towards the south and north, respectively (Berndt et al 2001), indicating melt supplies from a relatively confined magmatic source.…”

“…Furthermore, it appears that a number of the uplifted regions and the parts of the NAIP with the most voluminous igneous production for this period, namely in the NW British Isles, the Faroe Islands, (central-east) CE Greenland and the Disko region in W Greenland (Upton, 1988;Saunders et al 1997;Meyer, Van Wijk & Gernigon, 2007), were emplaced in the vicinity of old orogenic sutures and/or fronts from the Palaeozoic Caledonian Orogen, at suture zones between Archaean-Proterozoic terranes at the conjugate East Greenland-NW European margins and at the suture zone between the Archaean NagssugtoqidianRinkian Orogen in the Disko-Baffin Island area (Figs 1, 2, 3).…”

“…It has traditionally been considered to comprise the voluminous Palaeogene igneous rocks occurring at the conjugate E Greenland-NW European margins and in the W Greenland-Baffin Bay area (Upton, 1988;Saunders et al 1997;Meyer, Van Wijk & Gernigon, 2007 and references therein). Other contemporaneous magmatism occurred in the northernmost parts of Greenland (Kap Washington Group at c. 64 ± 3 Ma, (Estrada, Höhndorf & HenjesKunst, 2001) and in the W Barents Sea (Vestbakken Volcanic Province, c. 54 Ma, (Tsikalas, Eldholm & Faleide, 2002) (Fig.…”

Evolution of the Vøring Volcanic Margin

“…The entire series is interpreted as originating from a primary, strongly depleted mantle source that was later LIL-element enriched. The upper series has clear chemical affinities to the Paleogene plateau basalts within the North Atlantic Volcanic Province (NAVP) (Thompson et al, 1986;Upton, 1988), as well as to Holocene magmas from the Mohns and Knipovich ridges (Neumann and Schilling, 1984) and parts of the Reykjanes Ridge (Schilling et al, 1983).…”

“…The NAVP includes the lower Tertiary igneous rocks of the North Atlantic borderlands that were emplaced prior to, or during, the breakup of Eurasia and Greenland (Noe-Nygaard, 1974;Upton, 1988). The province is a broad volcanic zone from Great Britain across the Faeroes and East Greenland to Baffin Bay, hence being a "transverse" feature with respect to the North Atlantic Ocean.…”