Volcanism on the Eggvin Bank (Central Norwegian … on the Eggvin Bank (Central Norwegian-Greenland...

Journal of Geodynamics 38 (2004) 57–83

Volcanism on the Eggvin Bank (Central Norwegian-GreenlandSea, latitude∼71◦N): age, source, and relationship to

the Iceland and putative Jan Mayen plumes

Dieter F. Mertza,b,c,∗, Warren D. Sharpc, Karsten M. Haased

a Johannes Gutenberg-Universität, Institut für Geowissenschaften, 55099 Mainz, Germanyb Max Planck-Institut für Chemie, Postfach 3060, 55020 Mainz, Germany

c Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USAd Institut für Geowissenschaften der Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, 24118 Kiel, Germany

Received 8 December 2003; received in revised form 1 March 2004; accepted 5 March 2004

Abstract

The Eggvin Bank (Central Norwegian-Greenland Sea, latitude∼71◦N) is a topographically anomalous shallowarea with scattered volcanic peaks extending between the island of Jan Mayen and East Greenland and straddlingthe northern segment of the mid-Atlantic Kolbeinsey Ridge axis. Basalts dredged from the Eggvin Bank rangefrom variably depleted, tholeiitic, near-axis lavas to enriched, transitional-to-alkaline, off-axis seamount lavas. Interms of normalised incompatible element patterns, the most depleted, near-axis tholeiite is similar to neighbouringKolbeinsey Ridge basalts, whereas the off-axis, transitional-to-alkaline lavas are similar to other alkaline basaltsoccurring close to the Eggvin Bank region, e.g., those of Jan Mayen.

40Ar/39Ar step heating data indicate that the off-axis seamount lavas are coeval with other alkaline lavas eruptedin the Central Norwegian-Greeland Sea at ca. 0.6–0.7 Ma. In contrast, the Eggvin near-axis tholeiites are<0.1 Ma.Volcanic peaks west and north of Jan Mayen show no indication of a systematic age progression. Therefore, the JanMayen hot spot hypothesis is not supported by the available radiometric age data. Sr, Nd, and Pb isotope composi-tions of near-axis and off-axis Eggvin Bank lavas are distinct, implying differences in their mantle sources. Isotoperatios of the off-axis basalts (87Sr/86Sr = 0.70344–0.70352,143Nd/144Nd = 0.51283–0.51288,206Pb/204Pb =18.82–18.85) resemble those of neighbouring alkali basalt occurrences, however, isotope ratios of the near-axistholeiites correspond to lavas erupting in the south-eastern volcanic zone of Iceland, e.g., at Vestmannaeyjar. Thenear-axis tholeiites are generated by an unusual source with highly radiogenic Pb (206Pb/204Pb = 18.95) to-gether with relatively radiogenic Nd (143Nd/144Nd = 0.51295) and low-radiogenic Sr (87Sr/86Sr = 0.70314),respectively, representing an unique composition in the mantle north of central Iceland. The overlap in isotope

∗ Corresponding author. Tel.:+49-6131-3922857.E-mail address:[email protected] (D.F. Mertz).

0264-3707/$ – see front matter © 2004 Elsevier Ltd. All rights reserved.doi:10.1016/j.jog.2004.03.003

58 D.F. Mertz et al. / Journal of Geodynamics 38 (2004) 57–83

compositions between Eggvin Bank near-axis tholeiites and south-east Iceland alkaline lavas could be an indicationthat the Eggvin Bank tholeiite source was derived from the Iceland plume and that it was emplaced in the uppermantle by the original Iceland plume head during the Early Tertiary as suggested by Trønnes et al. [Trønnes, T.,Planke, S., Sundvoll, B., Imsland, P., 1999. Recent volcanic rocks from Jan Mayen: low degree melt fractions ofenriched north-east Atlantic mantle. J. Geophys. Res. 104, 7153–7167].

Isotope and trace element data indicate an abrupt change in source composition along the Kolbeinsey Ridge axis atlatitude ca. 70.6◦N, apparently reflecting a boundary between two chemically distinct mantle domains with limitedinteraction. Based on Pb versus Pb isotope diagrams, no dispersion of enriched material is observed adjacent to thehypothetical Jan Mayen/Jan Mayen Platform plume, neither to the north-east along the Southern Mohns Ridge norto the south along the Central Kolbeinsey Ridge.© 2004 Elsevier Ltd. All rights reserved.

1. Introduction

In 1983, Schilling et al. (1999)published a comprehensive major and trace element data set onMid-Atlantic ridge samples dredged from latitude 29◦N to 73◦N providing an overview on the geo-chemistry of the North Atlantic basalts from the ridge segments south of the Azores via Iceland up tothe north of Jan Mayen. Recently, the high-latitude part of this data set comprising the ridge segmentsnorth of Iceland, i.e., essentially Kolbeinsey, Mohns and Knipovich Ridges (Fig. 1) has been completedby isotope and additional trace element (Hanan et al., 2000) measurements. Together with new geochem-ical and isotope data on Iceland (e.g.,Hanan and Schilling, 1997; Chauvel and Hémond, 2000) and JanMayen (e.g.,Trønnes et al., 1999) volcanism, a consistent, large-scale picture of the composition of thehigh-latitude North Atlantic mantle has emerged.

In contrast, the nature of the mantle sources, their interactions and the causes of magma generationfor Eggvin Bank–Jan Mayen intraplate volcanism located between the northern Kolbeinsey Ridge andthe southern Mohns Ridge segments (Central Norwegian-Greenland Sea;Fig. 1) remains controversial.Jan Mayen volcanism has been interpreted as recent hotspot activity (e.g.,Johnson and Campsie, 1976;Morgan, 1983; Schilling et al., 1983; Vink, 1984) and the topographically anomalous shallow EggvinBank west of Jan Mayen (Fig. 1) with discontinuous volcanic peaks is thought to represent the Jan Mayenhot spot track (Morgan, 1981). Mohns Ridge spreading axis lavas occurring north of Jan Mayen—withradiogenic87Sr/86Sr and Pb isotope ratios, relatively unradiogenic143Nd/144Nd compositions, and in-compatible element enrichment relative to normal-type mid-ocean ridge basalt (N-type MORB)—areregarded as the result of contamination of their asthenospheric source by material from a hot mantleplume underneath Jan Mayen or the Jan Mayen Platform (Schilling et al., 1983, 1999; Neumann andSchilling, 1984). In contrast, seismic, tectonic, petrological, and geochemical data are interpreted to indi-cate that no anomalously hot mantle underlies the Jan Mayen region (e.g.,Imsland, 1980;Saemundsson, 1986; Havskov and Atakan, 1991; Haase et al., 1996). For example,Haase et al. (1996,2003)concluded that Jan Mayen magmas are generated by melting of volatile-enhanced, passively up-welling mantle influenced by the adjacent Mohns Ridge spreading axis (Fig. 1). Moreover, they suggestedthat the shallow bathymetry of the Eggvin Bank is caused by an iron-depleted mantle, which is less densethan its surrounding mantle.Trønnes et al. (1999)proposed that Jan Mayen magma originates fromlow-degree partial melts of enriched material emplaced in the NE Atlantic mantle by the ancestral Ice-land Plume at about 60 Ma.

D.F. Mertz et al. / Journal of Geodynamics 38 (2004) 57–83 59

Fig. 1. Map of the Eggvin Bank–Jan Mayen region (Central Norwegian-Greenland Sea) based onPerry (1986)showing ma-jor tectonic and bathymetric features as well as K–Ar (in italics) and40Ar/39Ar ages (Fitch et al., 1965; Mertz and Renne,1995; Upton et al., 1995; this work) on volcanic rocks. The inset presents the high-latitude North Atlantic with the EggvinBank–Jan Mayen region. Numbers in brackets indicate sampling locations (seeTable 1). Depth contours in meter, JMFZ: JanMayen Fracture Zone (indicated by hatching), SFZ: Spar Fracture Zone (ca. 69◦N), TFZ: Tjörnes Fracture Zone (ca. 67◦N),JMP: Jan Mayen Platform, JMR: Jan Mayen Ridge, JM: Jan Mayen Island, MR: Mohns Ridge, CKR: Central Kolbeinsey Ridge(ca. 69◦–70.6◦N, also termed Middle Kolbeinsey Ridge in other papers), NKR: North Kolbeinsey Ridge (ca. 70.6◦–72◦N, otherauthors apply the acronym NKR to the segment 69◦–72◦N), OSC: Overlapping Spreading Center (ca. 70.6◦N). Reykjanes Ridgeextends south of Iceland approximately at latitude 64◦–55◦N.

Only limited geochemical and geochronological data are available for Eggvin Bank lavas (Pedersenet al., 1976; Schilling et al., 1983, 1999; Campsie et al., 1990) and their relationship to lavas of Jan Mayenisland as well as those of neighbouring Kolbeinsey and Mohns Ridge is not clear. During FS Polarsternexpedition ARK VII/1 volcanic rocks from the Eggvin Bank region were dredged. Here we present new40Ar/39Ar step heating data, geochemical compositions and Sr, Nd, Pb isotope ratios on these rocks inorder to establish their ages, characterise their mantle sources, and evaluate source interactions.

2. Geological setting

Fig. 1 is a simplified map of the Eggvin Bank–Jan Mayen region showing relevant bathymetric andtectonic features. Jan Mayen is located in a topographically anomalous area at the northern end of theJan Mayen Ridge, which is at least in part a continental fragment (e.g.,Grønlie et al., 1979; Myhreet al., 1984). With the northward propagation of the mid-Atlantic Kolbeinsey Ridge about 43 Ma ago, thisfragment was split off from Greenland and drifted to its present position (Nunns, 1982). Vesteris seamountis an isolated volcanic edifice located about 350 km north-west of Jan Mayen that was built on MiddleEocene oceanic crust about 3000 m below sea level. To the west of Jan Mayen, the northern segment ofthe Kolbeinsey Ridge penetrates the Eggvin Bank, a shallow region with seamounts reaching up to fewtens of meters below sea level (Fig. 1). East Greenlandic basalts at latitude 72◦–75◦N (e.g.,Upton et al.,


1984) occur in the western extension of the Eggvin Bank–Jan Mayen shallow region.40Ar/39Ar datingof these basalts yields eruption ages of 57–58 Ma as well as later volcanic activity at ca. 32 Ma (Uptonet al., 1995). East Greenland basalts south of latitude 72◦N yield Paleogene K–Ar total rock ages with theoldest Paleocene ages of ca. 55–60 Ma being interpreted as geologically meaningful (Beckinsale et al.,1970).

The mid-Atlantic spreading axis is offset along the Jan Mayen Fracture Zone about 200 km from theKolbeinsey Ridge to the Mohns Ridge.Torske and Prestvik (1991)suggested that the Jan Mayen FractureZone is an old lithospheric fault system that provided pathways for volatiles and melts leading to alkalinemagmatism. North of the Mohns Ridge the Knipovich segment forms the Mid-Atlantic spreading axis.The Mohns Ridge directly north of the Jan Mayen Fracture Zone runs into the so-called Jan MayenPlatform (Neumann and Schilling, 1984), an approximately 60 km wide bank opposite Jan Mayen. TheNorth Kolbeinsey Ridge is separated from the Central Kolbeinsey Ridge by an overlapping spreadingCenter at ca. 70.6◦N. The Spar Fracture zone at latitude ca. 69◦N separates the Central Kolbeinsey Ridgefrom the South Kolbeinsey segment, which penetrates Iceland south of latitude ca. 67◦N.

More detailed tectonic, bathymetric, and geological descriptions of the Eggvin Bank–Jan Mayen regionare given by, e.g.,Johnson and Campsie (1976), Bungum and Husebye (1977), andSaemundsson (1986).The plate tectonic evolution of the Norwegian-Greenland Sea is presented inTalwani and Eldholm (1977)andEldholm et al. (1990).

3. Sampling

The samples were recovered by four dredge hauls. Detailed sampling data are given inTable 1, thegeographical position of the dredge hauls is presented inFig. 1. FS Polarstern dredges 21860 and 21861-3sampled Eggvin Bank near-axis seamounts while dredge 21862 sampled an Eggvin Bank off-axisseamount. In addition to the Eggvin Bank samples, a Mohns Ridge near-axis alkali basalt from the

Table 1Sampling data of basalts from the Eggvin Bank–Jan Mayen region (Norwegian-Greenland Sea)

Dredge#LocationCruise

StartLatitude Longitude

EndLatitude Longitude Water depth [m]

21860 70◦59.27′N 13◦58.39′W 70◦59.25′N 13◦59.01′W 404–367Eggvin BankPolarstern ARK VII/1

21861-3 70◦56.23′N 13◦01.05′W 70◦56.25′N 13◦00.95′W 38–35Eggvin BankPolarstern ARK VII/1

21862-B 71◦19.33′N 11◦08.92′W 71◦19.51′N 11◦09.42′W 542–464Eggvin BankPolarstern ARK VII/1

23295-3 71◦08.90′N 05◦54.89′W 71◦09.29′N 05◦53.74′W 1879–1773Jan Mayen PlatformMeteor 7/3


Jan Mayen Platform recovered by dredge 23295-3 of FS Meteor cruise 7/3 has been dated. During thedredge hauls sudden releases of the dredge wire tension indicated tearing off and sampling of in situ rocksrather than material transported by ice drift. Recovered rocks in each case were angular pillow fragments,sometimes with glassy rims. The freshest-looking samples from each dredge were selected for majorand trace element as well as for radiogenic isotope analyses. Thin section investigations revealed thatthe holocrystalline groundmasses of some samples show only minor alteration. Therefore, groundmassseparates of these rocks (tholeiites 21861-3-A, 21860-D, alkali basalts 21862-E, 23295-3) were processedfor radiometric age dating.

4. Analytical methods

Major elements were analysed by X-ray fluorescence (whole rocks) and electron microprobe (glassand minerals) at the Mineralogical Institute in Kiel following the procedures described byHaase et al.(1996). The trace element concentrations were determined by Inductively coupled plasma mass spec-trometry (ICP-MS) at the Geological Institute in Kiel on representative samples following the methodsof Garbe-Schönberg (1993). Results on standards analysed concurrently with the Eggvin Bank samplesare given inHaase et al. (1996).

40Ar/39Ar analyses samples, weighting∼200 mg, were loaded in Cu foil packages and irradiatedin the cadmium shielded port (CLICIT) at the Triga reactor at University of Oregon and analysed atBerkeley Geochronology Center. Values ofJ (a measure of neutron dosage) were determined from themean of 10 single-crystal laser fusion analyses of co-irradiated Fish Canyon sanidine, using an age of28.02 Ma (Renne et al., 1998). Corrections for interfering nucleogenic isotopes of Ar were determinedfrom analyses of irradiated CaF2 and a synthetic K-bearing glass (KFeSiO4) using the values given byRenne (1995). The samples were baked out at 250◦C for 10 h prior to analysis. The furnace is a doublevacuum type with a Ta resistance heater and a Mo crucible. Extraction line operation, including sampleheating, is fully automated. Blanks for the extraction line and furnace were measured and blank correctionwas applied as described bySharp et al. (1996). Reactive components, such as H2O, CO2, CO, and N2,were removed from the sample gas in two sequential stages using SAES GP-50 Zr–Al getters operatedat 400◦C. The purified gas was analysed using a Mass Analyser Products 215–50 mass spectrometer,configured for a resolution of 450. Mass discrimination was determined from repeated analyses of air Arusing an on-line pipette, yielding a mean value of 1.006± 0.0020 per atomic mass unit (amu) during thecourse of this study. The decay constants and isotopic ratios used are those given bySteiger and Jäger(1977). Uncertainties for ages are given at the 2σ level and include errors arising from irradiation and Aranalysis but do not include errors in decay constants or isotopic abundances of K and atmospheric Ar.

Sr, Nd, and Pb isotope analyses were carried out on hand-selected grains which were leached for 2 h withhot 6 N ultrapure HCl prior to dissolution. Sr and the rare earth element (REE) fractions were separatedusing conventional cation exchange procedures. Nd of the REE fraction was then separated on a secondcolumn containing Teflon powder coated with di-2-ethyl-hexyl orthophosphoric acid. Pb was separatedusing the technique described byManhès et al. (1978). The Sr, Nd, and Pb isotope compositions weremeasured at the Max Planck-Institut Mainz on a Finnigan MAT 261 mass spectrometer with static multi-collection. Sr and Nd isotope ratios are normalised to86Sr/88Sr = 0.1194 and to146Nd/144Nd = 0.7219.Pb isotope ratios are relative to values of206Pb/204Pb= 36.738,207Pb/204Pb= 17.159 and208Pb/204Pb=36.744 for NBS standard 982 and are corrected of 0.13% per amu. Total blank contributions were<0.4‰


for Pb,<0.2‰ for Nd and<0.008‰ for Sr, and are considered not to be significant. NBS standard SrCO3

987 and the La Jolla Nd standard have been measured, yielding87Sr/86Sr = 0.710241± 0.000011 (2σ)and143Nd/144Nd = 0.511842± 0.000009 (2σ), respectively. The sample isotope ratios given are notnormalised to the recommended standard values of87Sr/86Sr = 0.710248 and143Nd/144Nd = 0.511850.

5. Results

5.1. Petrography and mineral composition

The samples of dredge hauls 21860 and 21861-3 from Eggvin Bank near-axis seamounts show a largevariation in petrography ranging from aphyric samples to lavas containing less than 10% phenocrysts.Phenocrysts are generally plagioclase and olivine with rare clinopyroxene, e.g., in sample 21860-D. In con-trast, the Eggvin Bank off-axis lavas of dredge haul 21862 contain more than 30% phenocrysts of olivine,plagioclase and abundant clinopyroxene up to 4 mm in diameter. Olivine is relatively forsterite-rich withFo82 to Fo89. In hand specimen the large clinopyroxenes of some samples are dark green and these rocksare similar in petrography to Jan Mayen ankaramites (e.g.,Imsland, 1980). The clinopyroxene is a zonedTi–augite which in general shows higher MgO contents at the rim (ca. 15.6 wt.%) compared to the core(ca. 12.7 wt.%, sample 21826-B). The cores of some augites are resorbed and rounded xenocrysts occur.

5.2. Major and trace element geochemistry

Major and trace element analyses are presented inTable 2. Based on the TAS classification (Fig. 2) ofLe Maitre et al. (1989)Eggvin Bank near-axis lavas (dredges 21860 and 21861-3) are tholeiitic basaltscomparable to mid-ocean ridge basalts erupting on the neovolcanic zone of the neighbouring KolbeinseyRidge (e.g.,Schilling et al., 1983; Endres, 1992; Haase et al., 2003). In contrast, the Eggvin Bank off-axislavas (dredge 21862) represent nepheline-normative, mildly alkaline to transitional basalts—termed alkalibasalts herein for brevity—that are more typical for intraplate or off-axis seamounts (e.g.,Cousens, 1996;Niu et al., 1999). The major and trace element composition of Jan Mayen Platform alkali basalt 23295-3

Fig. 2. Total alkalis versus silica (TAS) classification for Eggvin Bank volcanic rocks. All analysed samples plot in the basaltfield (grey). Stippled line fromMacDonald and Katsura (1964)distinguishes between alkaline and tholeiite lava series based onvolcanic rocks from Hawaii. Open triangles: Eggvin Bank off-axis mildly alkaline to transitional basalts, open circles: EggvinBank near-axis tholeiites.


Table 2Chemical compositions of recovered glass (21860-B) and basalts (other samples) from the Eggvin Bank

Sample 2186-3-A 21861-3-B 21860-A 21860-B 21860-D 21860-F 21862- B 21862-C 21862-E 21862-F

SiO2 49.29 49.93 49.80 47.31 50.81 49.99 47.02 47.54 47.41 47.06TiO2 1.25 1.24 0.92 0.65 1.48 0.98 1.84 2.80 1.92 1.41Al2O3 15.09 15.33 13.91 16.02 14.47 14.82 13.41 17.26 10.13 14.55Fe2OT

3 11.05 11.06 12.85 10.06 13.11 11.87 10.02 11.75 9.95 9.99MnO 0.17 0.17 0.21 0.12 0.20 0.18 0.16 0.19 0.16 0.13MgO 7.35 7.32 8.32 9.83 5.81 7.98 12.65 4.75 13.78 8.11CaO 11.77 11.76 12.70 13.12 10.61 12.02 12.35 10.96 13.08 15.46Na2O 2.21 2.09 1.82 1.85 2.37 2.16 1.74 2.57 1.46 1.50K2O 0.62 0.61 0.09 0.05 0.54 0.10 1.11 1.28 1.33 0.50P2O5 0.24 0.25 0.19 n.d. 0.27 0.18 0.36 0.61 0.35 1.21

Total 99.04 99.76 100.81 99.01 99.67 100.28 100.66 99.71 99.57 99.92Mga 60.8 60.7 60.1 69.5 50.8 61.0 74.6 48.5 76.4 65.4

Sc 40.1 42.2 41.4 39.1 51.9 37.4 29.7 42.9Cr 42.3 77.7 362 11.3 92.3 731 56.8 847Co 45.2 52.5 45.6 51.1 48.8 52.3 36.0 53.4Ni 60.8 58.1 212 25.7 51.7 232 44.0 246Cu 122 92.7 106 87.0 99.2 57.0 95.0 93.3Zn 75.6 61.4 56.8 91.1 84.7 65.5 86.9 66.9Y 22.2 19.8 12.8 23.1 24.2 14.7 24.8 15.7Rb 14.4 1.82 1.15 11.2 0.82 25.3 23.7 33.3Cs 0.04 0.03 0.04 0.28 0.01 0.27 0.21 0.34Sr 172 63.9 92.6 180 64.0 479 538 407Ba 166 14.2 21.9 199 40.3 399 486 461Zr 82.9 36.2 27.7 81.2 38.3 125 201 138Hf 2.14 1.26 0.72 2.04 1.18 3.26 5.11 3.25Nb 20.1 6.18 4.69 35.9 5.10 47.8 64.4 45.0Ta n.d. n.d. n.d. n.d. n.d. 4.44 5.49 4.14Pb 0.92 0.37 0.35 1.07 0.37 1.48 2.31 1.61Th 1.31 0.25 0.11 1.36 0.13 3.36 4.37 2.98U 0.38 0.10 0.05 0.47 0.13 0.86 0.87 0.82

La 12.4 1.72 2.54 13.90 2.04 28.4 38.9 27.8Ce 25.0 4.65 5.80 28.70 5.24 55.0 85.6 56.6Pr 3.17 0.77 0.80 3.55 0.84 6.40 10.1 6.90Nd 12.8 4.51 3.81 14.20 4.50 24.5 40.0 26.1Sm 2.99 1.80 1.22 3.30 1.79 4.57 7.79 5.03Eu 1.02 0.71 0.53 1.15 0.73 1.41 2.35 1.53Gd 3.38 2.70 1.75 3.71 2.68 4.15 6.67 4.46Tb 0.56 0.54 0.32 0.63 0.52 0.63 1.00 0.66Dy 3.65 3.85 2.23 4.04 3.68 3.16 5.29 3.43Ho 0.77 0.85 0.49 0.86 0.80 0.62 1.01 0.65Er 2.28 2.57 1.43 2.55 2.42 1.67 2.75 1.72Tm 0.33 0.37 0.22 0.37 0.35 0.21 0.35 0.22Yb 2.22 2.57 1.40 2.45 2.41 1.38 2.31 1.41Lu 0.33 0.38 0.21 0.35 0.35 0.20 0.33 0.20(La/Sm)N 2.68 0.62 1.34 2.72 0.74 4.01 3.23 3.56

a Mg = 100× Mg2+/(Mg2++Fe2+) (atomic) and assuming FeO= Fe2OT3 × 0.85.

La/Sm normalised using C1 chondrite ofSun and McDonough (1989); n.d.: not determined.


Fig. 3. Chondrite-normalised La/Sm ((La/Sm)N, using C1 chondrite fromSun and McDonough, 1989) vs. MgO for lavas fromthe region north of Iceland indicating mantle heterogeneities. Data fromSun et al. (1979), Schilling et al. (1983), Neumann andSchilling (1984), Maaløe et al. (1986), Devey et al. (1994), Endres (1992), Haase et al. (1996, 2003)andTrønnes et al. (1999),this work.

has been published previously (Haase et al., 1996). Based on their chondrite-normalised La/Sm ratios[(La/Sm)N] varying from about 0.6–2.7 (Fig. 3), the Eggvin Bank near-axis tholeiites range from depleted[=(La/Sm)N < 1; N-type lava] to enriched [=(La/Sm)N > 1; E-type lava] similar to basalts from the MohnsRidge. The Eggvin Bank off-axis alkali basalts (Pedersen et al., 1976; this work) resemble Jan Mayen(Maaløe et al., 1986; Trønnes et al., 1999) and Jan Mayen Platform (e.g.,Neumann and Schilling, 1984)lavas in terms of incompatible element enrichment with (La/Sm)N of 3 to 4 (Fig. 3). Also, Eggvin Bankalkali basalts range in MgO from 4.7 to 13.8 wt.%, indicating that shallow level fractionation processesare comparable in importance to Jan Mayen magmas.

5.3. 40Ar/39Ar data

Three samples were analysed using the40Ar/39Ar incremental heating technique. The Ar results arepresented inTable 3, the corresponding age spectra are shown inFig. 4. Samples 21861-3-A and 21862-Eyielded plateau ages of 96±34 and 697±30 ka, respectively. A duplicate analysis of 21861-3-A yieldedan age of 99± 28 ka, in good agreement with the earlier determination. The plateau steps for samples21861-3-A and 21862-E yielded linear arrays on isochron diagrams (not shown) with mean square ofweighted deviations (MSWD) of 1.0 and 0.7,40Ar/36Ar initial ratios of 293.3 ± 4.2 and 294.3 ± 7.8,and ages of 113± 32 and 700± 48 ka, respectively.40Ar/36Ar initial ratios are within 1σ error ofthe atmospheric40Ar/36Ar ratio of 295.5, indicating that no excess40Ar was detected. Consideringanalytical errors, isochron and plateau ages of each sample are indistinguishable. Sample 23295-3 yieldeda discordant spectrum. The six “plateau” steps inFig. 4c, however, contain >60% of the total39Ar andtheir ages scatter only slightly more than allowed by the plateau criteria ofFleck et al. (1977). The meanage of these steps, weighted by their uncertainties, is 680± 83 ka. In an isochron diagram, these stepsscatter more than expected from analytical error (MSWD= 8.2). Nevertheless, the data define a trapped40Ar/36Ar ratio of 285± 15, indicating that there is no excess Ar related to this sample. The value of680± 83 ka is considered the best available estimate for the age of this lava. Conventional K–Ar dating


Table 3Step heating40Ar/39Ar data (J = 0.0001355) of basalts from the Eggvin Bank–Jan Mayen region

Temperature [◦C] 40Ar[Mol] 40Ar/39Ar 38Ar/39Ar 37Ar/39Ar 36Ar/39Ar 40Ar∗/39Ar 40Ar∗[%] Age [Ma] ±2σ

21861-3-A600 2.17E-16 205.540 2.0189 3.138 1.1518−134.877 −65.5 −33.276 478.598700 7.90E-14 46.512 0.0403 5.362 0.1583 0.156 0.3 0.038 0.110750 3.67E-14 13.681 0.0180 3.994 0.0458 0.471 3.4 0.115 0.041775 2.75E-14 10.061 0.0159 4.472 0.0343 0.270 2.7 0.066 0.035800 1.65E-14 6.549 0.0142 4.411 0.0220 0.399 6.1 0.097 0.030835 2.00E-14 5.888 0.0139 4.198 0.0194 0.478 8.1 0.117 0.024865 1.26E-14 5.657 0.0150 3.884 0.0188 0.416 7.3 0.102 0.032900 8.62E-15 7.160 0.0142 3.675 0.0226 0.770 10.7 0.188 0.0561000 2.05E-14 8.865 0.0168 1.997 0.0300 0.161 1.8 0.039 0.0351100 4.39E-14 34.458 0.0361 28.262 0.1247 −0.149 −0.4 −0.037 0.1081200 2.76E-14 33.762 0.0310 65.701 0.1298 0.693 1.9 0.169 0.1411400 2.40E-14 68.186 0.0445 87.895 0.2549 −0.123 −0.2 −0.030 0.382

21861-3-A (duplicate)600 3.38E-13 5120.777 3.2699 4.802 17.2513 23.502 0.5 5.736 58.471700 2.12E-12 351.335 0.2340 6.272 1.1829 2.287 0.6 0.559 0.680750 1.62E-15 11.790 0.0183 7.867 0.0546 −3.748 −31.6 −0.917 1.304775 3.79E-15 11.378 0.0199 7.110 0.0465 −1.800 −15.7 −0.440 0.583800 5.25E-14 16.482 0.0213 5.887 0.0557 0.483 2.9 0.118 0.074835 2.51E-14 4.686 0.0150 5.115 0.0158 0.440 9.4 0.108 0.040865 4.16E-14 4.768 0.0143 4.377 0.0160 0.396 8.3 0.097 0.026900 3.19E-14 3.619 0.0138 3.651 0.0117 0.451 12.4 0.110 0.0251000 3.83E-14 3.573 0.0143 2.466 0.0114 0.410 11.4 0.100 0.0201100 3.14E-14 5.411 0.0162 2.197 0.0179 0.288 5.3 0.070 0.0381200 1.12E-13 46.884 0.0488 92.772 0.1848 −0.340 −0.7 −0.083 0.1721400 1.14E-13 280.536 0.1979 119.446 0.9902 −2.776 −0.9 −0.679 1.419

23295-3600 5.22E-16 413.481 0.7720 0.000 0.9374 136.473 33 33.056 101.709650 5.95E-15 105.620 0.1387 0.663 0.3443 3.921 3.7 0.958 1.328700 1.16E-13 32.457 0.0376 0.888 0.0981 3.539 10.9 0.865 0.067730 1.13E-13 15.900 0.0254 1.362 0.0422 3.517 22.1 0.860 0.031760 7.02E-14 13.237 0.0074 2.319 0.0315 4.112 31 1.005 0.030800 1.12E-13 13.163 0.0224 3.673 0.0356 2.940 22.3 0.718 0.027840 8.25E-14 11.700 0.0226 5.796 0.0328 2.467 21 0.603 0.025900 5.99E-14 12.537 0.0243 7.045 0.0344 2.930 23.2 0.716 0.031950 3.86E-14 16.728 0.0273 5.890 0.0472 3.252 19.3 0.795 0.0481000 4.02E-14 18.752 0.0324 5.125 0.0569 2.327 12.4 0.569 0.0561100 1.09E-13 39.262 0.0477 24.037 0.1279 3.371 8.4 0.824 0.0871200 6.07E-14 55.167 0.0446 142.908 0.2078 5.368 8.5 1.312 0.2221300 1.49E-14 153.945 0.0816 148.434 0.5273 10.940 6.2 2.672 1.382

21862-E600 9.98E-16 24.435 −0.0078 1.269 0.0963 −3.915 −16 −0.957 3.804700 1.83E-13 9.106 0.0189 1.484 0.0215 2.867 31.4 0.701 0.015750 1.25E-13 14.311 0.0199 1.245 0.0392 2.842 19.8 0.695 0.028775 7.79E-14 14.044 0.0194 1.563 0.0379 2.961 21.1 0.724 0.034800 6.38E-14 15.602 0.0197 1.889 0.0433 2.948 18.9 0.721 0.044


Table 3 (Continued)

Temperature [◦C] 40Ar[Mol] 40Ar/39Ar 38Ar/39Ar 37Ar/39Ar 36Ar/39Ar 40Ar∗/39Ar 40Ar∗[%] Age [Ma] ±2σ

835 4.00E-14 15.098 0.0204 1.904 0.0428 2.613 17.3 0.639 0.059865 2.40E-14 13.006 0.0185 1.751 0.0361 2.483 19.1 0.607 0.079900 2.58E-14 14.426 0.0204 1.843 0.0415 2.312 16 0.565 0.0831000 7.81E-14 24.651 0.0278 2.747 0.0771 2.101 8.5 0.513 0.0651100 1.35E-13 28.688 0.0318 21.844 0.0942 2.650 9.1 0.648 0.0641200 2.51E-14 40.369 0.0348 35.088 0.1398 1.901 4.6 0.464 0.2671400 2.26E-14 90.008 0.0558 65.226 0.3118 3.241 3.4 0.792 0.723

(a)

(b)

(c)

Fig. 4.40Ar/39Ar age spectra showing incremental heating results on (a) Eggvin Bank near-axis tholeiite 21861-3-A, (b) EggvinBank off-axis alkali basalt 21862-E and (c) Jan Mayen Platform near-axis alkali basalt 23295-3. Errors are 2σ̃.

on sample 21860-D yielded an age of 0.08± 0.04 Ma (H.J. Lippolt, personal communication). The agesof 96 and 80 ka of samples 21861-3-A and 21860-D, respectively, represent Upper Pleistocene, the agesof 697 and 680 ka of samples 21862-E and 23295-3, respectively, represent Lower Middle Pleistocene.

5.4. Sr, Nd, Pb isotope composition

Sr, Nd, Pb isotope ratios from Eggvin Bank basalts are presented inTable 4. Additional Sr, Nd, and Pbisotope ratios from Eggvin Bank near-axis and off-axis basalts are published byMertz and Haase (1997)andSchilling et al. (1999)and are compiled inFig. 5together with our new data. In all isotope diagramsEggvin Bank off-axis alkali basalts and near-axis tholeiites define different data fields indicating distinctmantle sources for both rock groups. In the87Sr/86Sr versus143Nd/144Nd diagram (Fig. 5a) Eggvin Bankalkali basalts plot close to Jan Mayen volcanic rocks whereas Eggvin Bank tholeiites form a different data


Table 4Isotope compositions of Eggvin Bank basalts

Sample 21860-D 21862-B 21862-C

87Sr/86Sr 0.703140 0.703442 0.703521±2σ 0.000011 0.000013 0.000014

143Nd/144Nd 0.512948 0.512875 0.512828±2σ 0.000009 0.000009 0.000011

206Pb/204Pb 18.948 18.821 18.854±2σ 0.015 0.017 0.013

207Pb/204Pb 15.541 15.525 15.521±2σ 0.013 0.016 0.018

208Pb/204Pb 38.723 38.661 38.694±2σ 0.036 0.044 0.048

field with less radiogenic Sr and higher radiogenic Nd compared to the alkali basalt group, and with aminor overlap with Jan Mayen Platform lavas. Eggvin Bank tholeiites resemble Vestmannaeyjar alkalineand Hekla transitional lavas from the south-eastern volcanic zone of Iceland (Furman et al., 1991). Thereare also similarities to Icelandic lavas from Snaefell (Hards et al., 1995) and Torfajökull (Stecher et al.,1999) in 143Nd/144Nd, however, the Icelandic rocks are more radiogenic in Sr. In the206Pb/204Pb versus208Pb/204Pb (Fig. 5b) and206Pb/204Pb versus207Pb/204Pb (Fig. 5c) diagrams both Eggvin Bank groupseither overlap with or plot close to the highest-radiogenic Jan Mayen Platform lavas. As is the casefor Sr and Nd isotopes, the Eggvin Bank tholeiites Pb isotope variation is also similar to the IcelandicVestmannaeyjar and Hekla Pb.

Fig. 5. (a)87Sr/86Sr vs.143Nd/144Nd, (b)206Pb/204Pb vs.208Pb/204Pb, (c)206Pb/204Pb vs.207Pb/204Pb for Eggvin Bank volcanicrocks (alkaline/transitional basalts= filled triangles; tholeiites= filled circles) compared to lavas from Iceland (Snaefell= lavasclosest to the suggested Iceland Plume center; Torfajökull= lavas representing high-radiogenic Pb of Iceland array; data fieldsof Hekla redrawn fromFurman et al. (1995)) as well as from north of Iceland. Data fromIto et al. (1987), Furman et al. (1991),Mertz et al. (1991), Hards et al. (1995), Mertz and Haase (1997), Stecher et al. (1999), Schilling et al. (1999)andTrønnes et al.(1999)—open rhombuses of Jan Mayen field; DePaolo et al. (unpublished)—open squares of Jan Mayen field; this work. EggvinBank tholeiite TR139 27D-5g (Schilling et al., 1999) is not considered for the Eggvin Bank tholeiite field in (c) because of thesubstantial deviation in207Pb/204Pb from the remaining Eggvin Bank tholeiites.


Fig. 5. (Continued).

6. Geological discussion

6.1. Previous K–Ar and40Ar/39Ar ages

In Fig. 1 K–Ar and 40Ar/39Ar ages on volcanic rocks from the region between Jan Mayen and eastGreenland are shown. For the stratigraphically oldest Jan Mayen subaerial volcanic rock series, K–Artotal rock dating on olivine basalts yields an age of about 0.3–0.5 Ma (Fitch et al., 1965). The youngestvolcanic eruptions on Jan Mayen island are of recent date (e.g.,Saemundsson, 1986; Imsland, 1980). Ashlayers in cores recovered from the Iceland Plateau show that volcanic activity at Jan Mayen may extendback to 3.3 Ma (Lacasse et al., 1996). For the isolated Vesteris seamount, laser step heating40Ar/39Armeasurements on groundmass and mineral separates indicate two phases of alkaline volcanism at 30–60 kaand 0.5–0.7 Ma, respectively (Mertz and Renne, 1995). Thus, Jan Mayen and Vesteris volcanic activitiesoverlap within the age range<0.7 Ma.

In contrast to our40Ar/39Ar data for Eggvin Bank–Jan Mayen Platform lavas, conventional K–Armeasurements on samples dredged close to the Jan Mayen Fracture Zone and in the northern extensionof the Kolbeinsey Ridge (Campsie et al., 1990) do not show Quaternary ages. Clinopyroxenite yieldsages of 304 and 529 Ma, which were interpreted as an indication that a large area of the northern IcelandPlateau is underlain by basement of Caledonian age. However, because the argon budget of pyroxeneis commonly dominated by excess40Ar (e.g.,McDougall and Green, 1964; Schwartzman and Giletti,1977) the geological significance of these dates are questionable. Furthermore, K–Ar total rock ages ondolerite from the same dredge haul vary from about 7–19 Ma. This variation was interpreted to result


from variable Ar loss in rocks of Oligocene or Miocene age (Campsie et al., 1990) caused by the intrusionof alkali-rich veins, which yield ages of 6.5 and 7.5 Ma, respectively. These ages may be flawed becauseof several factors that cannot be resolved with the existing K–Ar data including the possible presenceof excess40Ar, K and/or Ar loss associated with alteration, and polymagmatic origins of some samples.Moreover, spurious apparent ages for Norwegian-Greenland Sea volcanic rocks resulting from K andAr mobility or excess40Ar have been noted previously (Mertz and Renne, 1995). Therefore, K–Ar agesindicating Tertiary intraplate magmatic activity in the Eggvin Bank–Jan Mayen region should be treatedwith caution.

6.2. Hypothetic hotspot track

Johnson and Campsie (1976)described a 300 km-wide seamount belt extending parallel to the JanMayen fracture zone and comprising the Eggvin Bank–Jan Mayen–Jan Mayen Platform region. This beltis considered to represent the track of the postulated Jan Mayen hotspot (Morgan, 1981). If so, an ageprogression in intraplate volcanic activity to the west of Jan Mayen would be expected. Although theEast Greenlandic (Fig. 1) Lower Tertiary volcanism (e.g.,Upton et al., 1995) would match this model,with the exception of the questionable Late Miocene conventional K–Ar ages on feldspar-rich veins indolerites (compare 6.1.), measured ages within this seamount belt are exclusively<0.7 Ma.40Ar/39Arplateau ages (reported herein) of 697± 30 and 680± 83 ka for Eggvin Bank sample 21862-E and JanMayen Platform sample 23295-3, respectively, together with a kaersutite plateau age of 640± 70 kafrom a Vesteris seamount tephrite (Mertz and Renne, 1995) indicate broadly contemporaneous intraplatealkaline volcanic activity from 640 to 700 ka (Lower Middle Pleistocene) distributed within a radius ofabout 350 km north and west of Jan Mayen (Fig. 1). The plateau age of 96± 34 ka of Eggvin Banktholeiite 21861-3-A, the conventional K–Ar age of 0.8 ± 0.4 Ma of Eggvin Bank tholeiite 21860-D(both reported herein), Vesteris seamount volcanic activity at 30–60 ka (Mertz and Renne, 1995), andJan Mayen Holocene activity indicate a younger phase of off-axis volcanism in the age range<0.1 Ma(Upper Pleistocene).

Intraplate volcanism forming seamounts can occur episodically over periods of 106–107 years (e.g.,Pringle et al., 1991) and volcanoes from island chains are known to erupt lavas long after being trans-ported over the location of the active hotspot (e.g.,Clague and Dalrymple, 1988). Such rejuvenated-stageeruptions are generally alkalic. This type of volcanism, for example occurring in the Hawaiian islandchain, is apparently related to rapid changes between uplift and subsidence because of the rapid motionof the Pacific plate (e.g.,Jackson and Wright, 1970; Clague and Dalrymple, 1987). Since the plates in theNorwegian-Greenland Sea move about 10 times slower (e.g.,Vogt, 1986), the fast plate model probablydoes not apply to the high-latitude North Atlantic region. In this case, the alkaline 680 and 697 ka lavas ofthe Eggvin Bank–Jan Mayen region are difficult to interpret as Hawaiian-type rejuvenated-stage alkalinevolcanism of a hot spot track.

Dredging of volcanic rocks between Eggvin Bank and East Greenland in order to test the hot spot trackhypothesis for the western part of this region is not possible because of thick sedimentary cover. Thevolcanic activity in the Eggvin Bank–Jan Mayen region, however, shows no indication of a systematicage progression for a ca. 400 km distance (Fig. 1). Therefore, the hot spot track model is not supported byour geochronological data. It rather appears that Quaternary intraplate volcanism produced lavas duringdiscrete time intervals at ca. 0.7 Ma and<0.1 Ma at various sites in the high-latitude Atlantic north of70◦N.


6.3. Source of Eggvin Bank and neighbouring segments

6.3.1. Primitive mantle-normalised compositionRatios of highly incompatible elements can be useful for monitoring source compositions because the

extent of fractionation from each other by partial melting and differentiation processes is relatively small.Primitive mantle-normalised incompatible elements of Eggvin Bank off-axis lavas produce subparallelpatterns with prominent negative Pb and positive Nb anomalies, respectively, and comprising concentra-tion ranges, e.g., 44–62 times primitive mantle for the highly incompatible Rb or 12–20 times primitivemantle for the less incompatible Sm. The incompatible element patterns of Eggvin Bank off-axis, JanMayen Platform as well as Jan Mayen island alkaline lavas are similiar and there is a resemblance toHIMU (high � (= 238U/204Pb))-type lavas (Fig. 6a). Although enriched mantle (EM)-type mantle sourcesoccur within the high-latitude Atlantic mantle (e.g.,Hanan and Schilling, 1997), they are not dominant inthe central Norwegian-Greenland Sea region. Eggvin Bank off-axis, Jan Mayen Platform and Jan Mayenalkaline lavas do not show the EM-typical enrichment in the highly incompatible elements Rb and Ba.

(a)

(b)

Fig. 6. Primitive-mantle normalised (Hofmann, 1988) incompatible element plot for (a) Eggvin Bank off-axis (samples 21862-B,-C, -E; grey pattern; this work) alkali basalts in comparison to Jan Mayen Platform near-axis (sample 23295-3;Haase et al.,1996), Jan Mayen (sample 167;Trønnes et al., 1999) and St. Helena HIMU (Sun and McDonough, 1989) lavas as well as for(b) Eggvin Bank near-axis tholeiites (sample 21861-3-A with high La/Sm of 4.15 and sample 21860-A with low La/Sm of 0.96;Table 2) in comparison to N-type MORB (Hofmann, 1988) and Central Kolbeinsey MORB (grey pattern;Endres, 1992).


Trønnes et al. (1999)suggested that there is a HIMU component in the North Atlantic upper mantle,which could represent recycled oceanic crust entrained in the ancestral Iceland plume and which has beendistributed laterally by the ancestral plume head.Thirlwall (1995)has interpreted the Icelandic Pb isotopevariation in terms of mixing between a single immature HIMU composition or a range of immature HIMUcompositions, respectively, with an unradiogenic plume source represented by NE Icelandic picrites fromTheistareykir. The Eggvin Bank off-axis incompatible element patterns confirm that HIMU-influencedmantle domains are a common feature of the high-latitude North Atlantic mantle.

Fig. 6b shows the incompatible element patterns of the Eggvin Bank near-axis tholeiites with thelowest (sample 21860-A) and highest La/Sm ratios (sample 21861-3-A) of our data set, compared toCentral Kolbeinsey as well as to N-type MORB. The highly incompatible element concentrations Rband Ba of the Eggvin Bank tholeiites are similar (21860-A) to or enriched (21861-3-A) by a factor of27 relative to N-type MORB. In terms of the medium and heavy rare earth elements (Sm to Lu) andY the Eggvin Bank tholeiites are depleted compared to N-type MORB and sample 21860-A matchesaverage Central Kolbeinsey MORB. This suggests that the near-axis lavas probably were generatedon the North Kolbeinsey spreading axis and represent old oceanic crust rather than recently formed in-traplate volcanism. Consequently, the enriched material presently observed beneath the North Kolbeinseyspreading axis (Haase et al., 2003) must have been present for at least 100 ky beneath this part of themid-Atlantic Ridge. The Eggvin Bank tholeiites show positive Nb as well as negative Pb anomaliesas it is the case with Eggvin Bank alkaline lavas indicating similarities between off-axis and near-axislavas.

6.3.2. Radiogenic isotope variationThe diagrams206Pb/204Pb versus207Pb/204Pb (Fig. 5c) and207Pb/204Pb versus208Pb/204Pb (Fig. 7)

demonstrate different Pb isotope ratios for the Eggvin Bank and Jan Mayen lavas indicating differentmantle sources for both sites. The Eggvin Bank Pb is more radiogenic compared to Jan Mayen. In

Fig. 7.207Pb/204Pb vs.208Pb/204Pb for Eggvin Bank, Jan Mayen and Jan Mayen Platform volcanic rocks compared to MORB fromthe neighbouring spreading axes to the northeast (Southern Mohns Ridge, 71.5◦–72.5◦N) and to the south (Central KolbeinseyRidge, 69.0◦–71.5◦N). Symbols as inFig. 5. Data fromIto et al. (1987), Mertz and Haase (1997), Schilling et al. (1999)andTrønnes et al. (1999), this work.


(a)

(b)

Fig. 8. (a)206Pb/204Pb vs.143Nd/144Nd and (b)206Pb/204Pb vs.87Sr/86Sr for Eggvin Bank volcanic rocks compared to lavas fromIceland as well as from north of Iceland. Symbols and references as inFig. 5. Hatched straight lines separate mantle segmentslocated north of central Iceland from those located south of central Iceland. See text for discussion of Eggvin Bank tholeiite datafields. Slopes for hatched straight lines arey = −3.6 × 10−4x + 0.51976 in (a) andy = 6.9 × 10−4x + 0.69031 in (b).

addition, the isotope diagrams (Figs. 5, 7 and 8) show that the neighbouring Central Kolbeinsey andSouthern Mohns Ridge sources are also different from Eggvin Bank as well as from Jan Mayen/JanMayen Platform sources, respectively. In general, at a given207Pb/204Pb ratio, the Central KolbeinseyRidge has less radiogenic206Pb/204Pb and208Pb/204Pb ratios than the Southern Mohns Ridge, whereasthe Southern Mohns Ridge has less radiogenic206Pb/204Pb and208Pb/204Pb ratios than Jan Mayen/JanMayen Platform, resulting in a subparallel arrangement of Central Kolbeinsey Ridge, Southern MohnsRidge as well as Jan Mayen/Jan Mayen Platform data fields (Figs. 5c and 7).

On the basis of Sr, Nd, and Pb isotopic variationsMertz and Haase (1997)found a distinct large-scalepattern within the high-latitude North Atlantic mantle. At a given Pb isotope composition, ridge as wellas intraplate lavas from the region of north of central Iceland up to the Arctic Ocean have more radiogenicSr and less radiogenic Nd than lavas from south of central Iceland. This pattern is demonstrated inFig. 8using selected high-latitude mantle segments for comparison together with the Eggvin Bank samples.Whereas the Eggvin Bank alkali basalts correspond to the outlined large-scale isotope pattern, the EggvinBank tholeiites originate from a distinct source which is different from the “normal” mantle sourcenorth of central Iceland. The compositions of the Eggvin Bank tholeiites—high-radiogenic Pb and Nd,respectively, and low-radiogenic Sr—corresponds to lavas found in the south-eastern Icelandic volcaniczone (e.g., Vestmannaeyjar).


6.4. Source heterogeneities and mantle domains

It has been shown previously using trace element (e.g.,Schilling et al., 1983) and isotope compositions(Mertz and Haase, 1997; Schilling et al., 1999) that heterogeneous mantle sources feed modern volcan-ism in the North Atlantic north of latitude ca. 70.6◦N. Our new data show that these heterogeneitiesaffected the North Kolbeinsey spreading axis since at least 100 ky (e.g.,Figs. 3 and 5). The lavas fromthe Eggvin Bank region close to the Jan Mayen Fracture Zone are generally enriched in incompatibleelements (Dittmer et al., 1975; Pedersen et al., 1976; Sun et al., 1979; Schilling et al., 1983; Neumannand Schilling, 1984). For example, these lavas show an increase in (La/Sm)N up to ca. 4 whereas fur-ther south the Eggvin Bank erupts lavas with(La/Sm)N < 1 (Fig. 9b). In addition to the increase in(La/Sm)N approaching the Jan Mayen Fracture Zone, volcanic rocks north of latitude 70.6◦N in general

(a)

(b)

(c)

Fig. 9. (a) Variation of Na8.0, (b) (La/Sm)N and (c) Ba/La vs. latitude along the spreading axes between 66◦ and 78◦N indicatinga general northward decrease of the degree of melting and a more enriched mantle north of 70.6◦N. Data fromSun et al. (1979),Sigurdsson (1981), Schilling et al. (1983), Neumann and Schilling (1984), Melson and O’Hearn (1986), Waggoner (1989),Devey et al. (1994), Haase et al. (1996, 2003)andTrønnes et al. (1999), this work.


have higher Ba/La ratios of ca. 10–20 compared to ca. 5–10 of MORB from the central and southernKolbeinsey Ridge segments south of latitude 70.6◦N (Fig. 9c). This compositional contrast is also demon-strated by substantial offsets in isotope compositions occurring at latitude 70.6◦N. Fig. 10a–d shows that87Sr/86Sr,143Nd/144Nd,206Pb/204Pb as well as3He/4HeR/Ra of Kolbeinsey lavas (latitude 68.0◦–70.6◦N)are different from Eggvin Bank near-axis tholeiites and from Eggvin Bank off-axis alkali basalts (latitude>70.6◦N). For example, Central Kolbeinsey Ridge87Sr/86Sr and206Pb/204Pb ratios increase from approx-

(a)

(b)

(c)

Fig. 10. Variation of Sr, Nd, Pb and He isotope ratios versus latitude along the spreading axes between 68◦ and 73◦N indicating adepleted source with little variation south of an overlapping spreading center at ca. 70.6◦N where as the source north of 70.6◦N isenriched and shows a large variation except of He. Grey ranges highlight major trends in the isotope composition of rocks fromthe segment south of 70.6◦N in contrast to the Eggvin Bank near-axis and off-axis volcanic rocks. Data fromPoreda et al. (1986),Ito et al. (1987), Mertz et al. (1991), Macpherson et al. (1997), Mertz and Haase (1997), Trønnes et al. (1999)andSchilling et al.(1999), this work. SFZ: Spar Fracture Zone at latitude ca. 69◦N, OSC: Overlapping Spreading Center at latitude ca. 70.6◦N,JMFZ: Jan Mayen Fracture Zone at latitude ca. 72◦N (at longitude ca. 12◦W).


imately 0.7027–0.7030 and 17.9–18.1, respectively, to Eggvin Bank tholeiite ratios of 0.7031–0.7032 and18.8–19.0, respectively, and to Eggvin Bank alkaline lava ratios of 0.7034–0.7035 and 18.8–18.9, respec-tively. There is a single site at ca. 70.3◦N where Kolbeinsey lavas tap a more enriched mantle, e.g., withan206Pb/204Pb ratio of 18.34 (Ito et al., 1987), relative to the otherwise unradiogenic Kolbeinsey mantle.

The change in source composition at latitude 70.6◦N correlates geographically with overlapping spread-ing Center segments of the Central and North Kolbeinsey Ridges (Appelgate, 1997). A similar correlationis known from the northern Juan de Fuca Ridge (Cousens, 1996; Karsten et al., 1986, 1990). Schillinget al. (1999), based on the interpretation of geographical variations and trends in He–Pb–Nd–Sr isotopespace, suggested that there is a boundary in the vicinity of the Spar Fracture Zone at latitude ca. 69◦Nbetween the zones of influence of a postulated Jan Mayen plume characterised by low3He/4He ratios andthe Iceland plume with high3He/4He ratios. However, since the isotopic compositions along the Kol-beinsey Ridge up to latitude 70.6◦N are unusually homogeneous (Fig. 10), we infer a boundary betweentwo mantle domains beneath the Kolbeinsey Ridge at 70.6◦N.

There is a general resemblance between alkaline Eggvin Bank, Jan Mayen Platform and Jan Mayen lavasnorth of 70.6◦N in terms of normalised incompatible element patterns (Fig. 6) or high time-integratedU/Pb and Th/Pb element ratios producing highly radiogenic Pb compared to most other high-latitudeNorth Atlantic volcanic rocks (Mertz and Haase, 1997). However, the isotope ratios vary between thethree sites with substantial differences especially between Eggvin Bank and Jan Mayen lavas (Figs. 5and 7), indicating that the magma source composition is heterogeneous not only with latitude but alsowith longitude between 7◦ and 15◦W (at latitude ca. 71◦N).

6.5. Source interactions and mantle flow

A prominent mantle model for the Mohns Ridge-Jan Mayen Platform-Kolbeinsey Ridge region suggestsan enriched mantle plume located below the Jan Mayen Platform (Schilling et al., 1999) or below JanMayen Island (e.g.,Schilling et al., 1983) which is dispersing outward at shallow depth and is progressivelydiluted by mixing with the surrounding depleted asthenosphere. This model of binary mixing is supportedby geochemical trends based on certain isotope or trace element ratios as shown inFig. 11. However, forevaluating such source mixing processes it is more useful to apply isotope diagrams using the samex-axisandy-axis denominators (e.g., Pb versus Pb isotope diagrams inFigs. 5 and 7) because in this type ofdiagram binary mixing should result in linear arrays and is therefore simply to identify. In the case of centralNorwegian-Greeland Sea volcanism, these Pb versus Pb isotope diagrams show subparallel data fields forJan Mayen/Jan Mayen Platform on one hand and Southern Mohns Ridge as well as Central KolbeinseyRidge, respectively, on the other hand in206Pb/204Pb versus207Pb/204Pb (Fig. 5c) and207Pb/204Pb versus208Pb/204Pb (Fig. 7) spaces with a slightly shallower slope for the Central Kolbeinsey Ridge in the latterdiagram. The subparallel arrangement indicates that Jan Mayen/Jan Mayen Platform does not mix withthe neighbouring ridge segments, i.e., enriched Jan Mayen/Jan Mayen Platform material disperses neitherto the north-east along the Southern Mohns Ridge nor to the south along the Central Kolbeinsey Ridge.Thus, the curves presented inFig. 11cannot be interpreted to represent trends caused by binary sourcemixing.

Systematic errors in Pb isotope measurements can occur if instrumental mass fractionation is notappropriately corrected. The effect of 0.1% per atomic mass unit mass fractionation is demonstrated bytrajectories in the Pb versus Pb isotope diagrams shown. The true Pb isotope composition of any samplelies along a line plotted through the measured composition with similar length as and parallel to the


Fig. 11.206Pb/204Pb vs. (La/Sm)N for segments between latitude 69◦ and 73◦N. Roman figures indicate hypothetic binary mixingtrends between depleted Southern Mohns Ridge and enriched Jan Mayen sources (I) or depleted Central Kolbeinsey Ridge andenriched Jan Mayen Platform sources (II). However, based on Pb vs. Pb isotope diagrams these hypothetic mixing trends can beexcluded. See text for discussion. Data fromSchilling et al. (1983), Neumann and Schilling (1984), Mertz et al. (1991), Endres(1992), Devey et al. (1994), Haase et al. (1996), Mertz and Haase (1997)andTrønnes et al. (1999), this work.

instrumental mass fractionation trajectory. InFig. 5cit would theoretically be possible to create a moreor less linear Central Kolbeinsey Ridge-Southern Mohns Ridge-Jan Mayen/Jan Mayen Platform array byassuming not only extreme but also contrasting instrumental mass fractionation effects for the Kolbeinseydata on one hand and the Jan Mayen data on the other hand. However, replicate measurements of selectedKolbeinsey samples using a Pb double spike indicates that uncorrected instrumental mass fractionationeffects are insignificant (M. Thirlwall, personal communication). We therefore assume that this is alsothe case for the other compiled Pb isotope data. Furthermore, the mass fractionation trajectories liesapproximately parallel to the data fields (Fig. 7). Thus, the subparallel arrangement of the data fields isnot an analytical artifact but appears to be geologically meaningful.

In cases where mantle plumes are thought to feed enriched material into neighbouring spreading axes,regular geochemical and isotope gradients are observed along the ridge axes, for example, the Galapagosor Easter plumes (Verma et al., 1983; Hanan and Schilling, 1989; Fontignie and Schilling, 1991). Such apattern, however, is not seen along the Eggvin Bank-Kolbeinsey Ridge segment. As shown onFig. 10,the geographically discrete offset in isotope ratios at latitude 70.6◦N does not support the assumption ofsignificant interaction between a hypothetical Jan Mayen/Jan Mayen Platform plume-type mantle andthe Central Kolbeinsey MORB mantle.

Mohns Ridge MORB with(La/Sm)N > 1, Ba/La > 10 (Fig. 9) and87Sr/86Sr of 0.7029 (Schillinget al., 1999) occur as far north as ca. 77◦N indicating the presence of an enriched source more than 600 kmnorth of Jan Mayen. Considering the Jan Mayen/Jan Mayen Platform plume model ofSchilling et al.(1983, 1999)would mean that a far-reaching unilateral pollution of the upper mantle to the north by thesuggested plume occurred. However, no clear gradient in incompatible element ratios (Fig. 9) or in Sr, Nd,and He isotope ratios (Fig. 10) exists along the Mohns Ridge axis. Instead, a large variation in compositionsof the basalts is observed close to Jan Mayen while MORB further north show slightly less variation andthe most enriched lavas are lacking. As an alternative to the model of recent asthenospheric contaminationby plume material, we suggest that the observed incompatible element and isotope ratio variation couldarise from older small-scale heterogeneities in the upper mante, possibly caused by variable mixing of


small-degree melts from enriched parts of the mantle with large-degree melts from relatively depletedmantle peridotite.

In all Pb versus Pb isotope diagrams (Figs. 5 and 7) Jan Mayen, Jan Mayen Platform and EggvinBank lavas are linearly arrayed with the Jan Mayen Platfom rocks lying between the less radiogenic JanMayen and the more radiogenic Eggvin Bank data fields. In contrast, in87Sr/86Sr versus143Nd/144Ndspace (Fig. 5a) Jan Mayen lavas have more enriched signatures and Eggvin Bank near-axis tholeiiteshave less enriched signatures than lavas of the Jan Mayen Platform whereas the Eggvin Bank off-axisalkali basalts are similar to Jan Mayen/enriched Jan Mayen Platform volcanic rocks. The above JanMayen-Jan Mayen Platform-Eggvin Bank array can be explained if most of the Jan Mayen Platformlavas result from mixing between Jan Mayen alkaline lava and Eggvin Bank tholeiite sources. Thisprocess requires that the influence of the Jan Mayen mantle component extend for several tens of kmin a north-west and north-east direction, and that the influence of the Eggvin Bank mantle componentextend up to a few 100 km to the east–northeast. In this case, source interactions between differentsegments would mainly occur in the mantle below the Jan Mayen Platform and along the suggested man-tle flow paths below the topographically shallow region extending ca. 400 km E–W from the EggvinBank to the Jan Mayen Platform between latitude ca. 70.6◦–72◦N and longitude ca. 5◦–15◦W, re-spectively, rather than to the south along the Kolbeinsey Ridge or to the north-west along the MohnsRidge.

6.6. Melt generation

Klein and Langmuir (1987)suggested that variation of the fractionation-corrected Na2O (Na8.0) con-centrations in MORB reflects the degree of mantle melting which in turn depends largely on temperaturevariations. That is, low Na8.0 values indicate high degrees of partial melting (and high temperatures)while high Na8.0 values indicate the opposite, though some dependence on source composition has alsobeen shown (Niu et al., 2001). Nevertheless, the variation of Na8.0 versus latitude along the KolbeinseyRidge between 66◦ and 78◦N (Fig. 9a) indicates that melting temperature probably exerts the dominanteffect since Na8.0 content increases relatively smoothly towards the north despite more complex changesin source enrichment as indicated by variable (La/Sm)N (Fig. 9b). The high Na8.0 north of Jan Mayenimplies lower degrees of partial melting, which is consistent with the relatively thin crust of 4.0± 0.5 kmof the Mohns Ridge at latitude 72.0◦–72.5◦N measured by refraction seismic (Klingelhöfer et al., 2000).The low degree of melting beneath the Mohns Ridge and its thin crust adjacent to Jan Mayen indicate thatthe underlying mantle is comparatively cold, which is inconsistent with the influence of the putative JanMayen/Jan Mayen Platform plume. Moreover, ridge crust thought to be influenced by the Iceland plumeis thicker by a factor of about 2 than the crust of Mohns Ridge. For example, seismic experiments showthat crust on the Reykjanes Ridge axis near latitude 62◦N is ca. 8–10 km thick (Smallwood et al., 1995),and that∼1 Ma old crust on the east flank of the Kolbeinsey Ridge at latitude 70◦N is about 9 km thick(Kodaira et al., 1997).

Basalts from the Mohns and Knipovich spreading axes have a high average H2O/Ce of 287± 33(Michael, 1995), probably implying high water contents in their mantle sources. Based on experimentaldata,Stolper and Newman (1994)andHirose and Kawamoto (1995)suggested that the addition of 0.1%H2O to mantle peridotite increases the degree of partial melting by about 6%. Accordingly, we suggestthat the high H2O contents in the North Atlantic mantle north of 70.6◦N together with the setting ofJan Mayen opposite an active spreading axis may be responsible for the excess melting in this intraplate


region. Smaller intraplate volcanoes like the Eggvin Bank off-axis seamount may form close to thespreading axis when the enriched parts of the mantle begin to melt during mantle ascent close to the axisas envisaged by the model ofDavis and Karsten (1986).

6.7. Nature of Eggvin Bank mantle

One part of the mantle domain north of 70.6◦N tapped by the Eggvin Bank alkali basalts is related tothe source of the enriched Jan Mayen Platform lavas. The other part tapped by the Eggvin Bank tholeiitesis similar to the Icelandic mantle based on consistent Sr–Nd–Pb isotope compositions of lavas fromVestmannaeyjar/south-east Iceland and Eggvin Bank (Figs. 5 and 8). However, it is difficult to explainhow the feeding of the Eggvin Bank mantle by Vestmannaeyjar mantle plums at shallow depth could work.A lateral dispersion of Icelandic plume material by channelling along the Kolbeinsey Ridge (e.g.,Yale andPhipps Morgan, 1998) or by radially symmetric (Ito et al., 1996) mantle flow has been suggested. In thiscase, since no enriched south-eastern Iceland plume-type Vestmannaeyjar source with highly-radiogenicPb is tapped along the entire Kolbeinsey Ridge from the Tjörnes Fracture Zone at latitude 67◦ up to theoverlapping spreading Center at 70.6◦N (Fig. 1), the hypothetical north-directed Iceland plume flow mustlie deeper than the solidus along the Kolbeinsey Ridge as suggested byMertz et al. (1991). This scenariois based on the model of, e.g.,Batiza and Vanko (1984)assuming that enriched plums occur in a matrixof depleted asthenosphere. On the other hand, the transport of plums mainly depends on the regionaldirection of mantle flow (e.g.,Zhang and Tanimoto, 1992). Considering the plate tectonic setting ofVestmannaeyjar within the active southeast volcanic zone of Iceland together with the interpretation thatsouth-pointing V-shaped bathymetric morphologies along the Reykjanes Ridge south of Iceland indicateasthenosphere flow to the south (e.g.,Vogt, 1971), hypothetic Vestmannaehyjar plums most probably canbe regarded as components of the regional mantle flow regime to the south rather than being transportedto the north. For example,Yale and Phipps Morgan (1998)modelled flow rates to the south along theReykjanes Ridge as high as 30 cm/y for a low viscosity asthenosphere.

Therefore, in contrast to the assumption that the Eggvin Bank tholeiite source represents a mantlecomponent recently derived from the presently stationary Iceland plume, we concur withTrønnes et al.(1999) that this source was emplaced in the upper mantle by the original Early Tertiary plume head.This relationship between Eggvin Bank and southeast Iceland plume sources is indicated by a substantialoverlap in Sr–Nd–Pb isotope compositions of samples from both segments and on the assumption that theisotope composition of the Iceland plume essentially has been constant during its life time (e.g.,Thirlwallet al., 1994) from the plume head impinging on the lithosphere to the present on-axis setting.

7. Conclusions

Basalts dredged from the Eggvin Bank include tholeiitic, near-axis lavas and transitional-to-alkaline,off-axis seamount lavas. The Eggvin Bank tholeiites are variably enriched, with their chondrite-normalisedLa/Sm ratios ranging from about 0.6 to 2.7. The most depleted tholeiite is geochemically similar to basaltsfrom the neighbouring Kolbeinsey Ridge. The incompatible element patterns of Eggvin Bank off-axislavas are similiar to other alkaline basalts occurring close to this region (e.g., Jan Mayen, Jan MayenPlatform) and are derived from a HIMU-type source. As suggested previously, our data confirm that thereare large chemical heterogeneities in the mantle north of latitude ca. 70.6◦N.


Sr–Nd–Pb isotope diagrams allow differentiation between mantle sources of Eggvin Bank near-axisand off-axis lavas. The Eggvin Bank off-axis basalts resemble neighbouring alkali basalts in both isotopeand incompatible element patterns indicating a distinctive mantle source for a region extending over atleast 100 km. In contrast, the near-axis tholeiites resemble lavas from the southeastern volcanic zone ofIceland (e.g., Vestmannaeyjar). These differences show that in the Norwegian-Greenland Sea the magmasources are heterogenous not only with latitude but also with longitude, at least in the Eggvin Bank–JanMayen region between ca. 7◦ and 15◦W.

The inferred source of Eggvin Bank off-axis lavas is consistent with the large-scale isotope patternwithin the high-latitude North Atlantic mantle that has previously been described. The Eggvin Banknear-axis tholeiites, however, are generated by an distinct source characterised by highly-radiogenic Pband Nd and relatively low-radiogenic Sr. This compositional pattern is unique in the mantle north ofcentral Iceland. Based on the similiar Sr–Nd–Pb isotope compositions of Eggvin Bank tholeiites andsoutheast Iceland Vestmannaeyjar alkaline lavas, we conclude that the Eggvin Bank tholeiite sourcecould be related to the Icelandic plume mantle. Following the model ofTrønnes et al. (1999), we suggestthat the Eggvin Bank tholeiite source was emplaced in the upper mantle by the original Iceland plumehead during the Early Tertiary.

Isotopic and trace element data for near-axis tholeiites indicate an abrupt change in source com-positions at ca. 70.6◦N. This compositional change coincides geographically with an overlap of thenorthern and central segments of the Kolbeinsey Ridge and apparently reflects a boundary betweentwo chemically distinct mantle domains. Trace element and isotope data show no evidence for inter-actions between the different mantle sources north and south of 70.6◦N. Therefore, the existence ofan enriched Jan Mayen/Jan Mayen Platform plume feeding the Kolbeinsey ridge axes to the south isquestionable.

Lavas of the Jan Mayen/Jan Mayen Platform, the Southern Mohns Ridge, and the Central KolbeinseyRidge, define subparallel arrays on Pb versus Pb isotope diagrams. This indicates that the Jan Mayen/JanMayen Platform source has not mixed with the sources of the neighbouring ridge segments, i.e., enrichedJan Mayen/Jan Mayen Platform material disperses neither to the north-east beneath the Southern MohnsRidge nor to the south beneath the Central Kolbeinsey Ridge. It appears that source interactions mainlyoccur in the Jan Mayen Platform mantle possibly between Eggvin Bank tholeiite and Jan Mayen alkalibasalt sources.

40Ar/39Ar step heating data indicate that approximately contemporaneous intraplate alkaline volcanismwas broadly distributed within a ca. 400 km radius north and west of Jan Mayen at ca. 0.6–0.7 Ma as wellas younger, near-axis tholeiitic and intraplate alkaline activity at<0.1 Ma, respectively. If previouslypublished Miocene K/Ar ages for alkaline basalts dredged close to the Jan Mayen Fracture Zone areaccurate, it appears that the Eggvin Bank–Jan Mayen intraplate region produced significant volumes ofalkaline melts intermittently from the Miocene to recent. The available age data do not support the JanMayen hot spot track hypothesis, since volcanic peaks west and north of Jan Mayen show no indicationof a systematic age progression.

Acknowledgements

Captains, officers, and crews of FS Polarstern and FS Meteor are thanked for their skillful assistence withdredge operations. Thorough and helpful reviews by B.L. Cousens, K. Hoernle and an anonymous reviewer


as well as constructive discussions with R. Kraus are highly appreciated. We thank P. Koppenhöfer forhelp with drawing the figures and W. Jacoby for his patient editorial handling with an earlier versionof the paper. D. DePaolo made unpublished data on Jan Mayen accessible. The Polarstern and Meteorcruises were funded by the Bundesministerium für Bildung und Forschung (BMBF).

References

Appelgate, B., 1997. Modes of axial reorganization on a slow-spreading ridge: the structural evolution of Kolbeinsey Ridge since10 Ma. Geology 25, 431–434.

Batiza, R., Vanko, D., 1984. Petrology of young Pacific seamounts. J. Geophys. Res. 89, 11235–11260.Beckinsale, R.D., Brooks, C.K., Rex, D.C., 1970. K–Ar ages for the Tertiary of East Greenland. Bull. Geol. Soc. Denmark 20,

27–37.Bungum, H., Husebye, E.S., 1977. Seismicity of the Norwegian Sea: the Jan Mayen Fracture Zone. Tectonophysics 40, 351–

360.Campsie, J., Rasmussen, M.H., Kovacs, L.C., Dittmer, F., Bailey, J.C., Hansen, N.O., Laursen, J., Johnson, L., 1990. Chronology

and evolution of the northern Iceland Plateau. Polar Res. 8, 237–243.Chauvel, C., Hémond, C., 2000. Melting of a complete section of recycled oceanic crust: Trace element and Pb isotopic evidence

from Iceland. Geochem. Geophys. Geosyst. 1doi:10.1029/1999GC000002Clague, D.A., Dalrymple, G.B., 1987. The Hawaiian-Emperor volcanic chain, Part I, Geologic evolution. U.S. Geol. Survey

Professional Paper 1350, 5–54.Clague, D.A., Dalrymple, G.B., 1988. Age and petrology of alkalic postshield and rejuvenated-stage lava from Kauai. Hawaii.

Contrib. Mineral. Petrol. 99, 202–218.Cousens, B.L., 1996. Depleted and enriched upper mantle sources for basaltic rocks from diverse tectonic environments

in the northeast Pacific Ocean: the generation of oceanic alkaline vs. tholeiitic basalts. In: Basu, A., Hart, S.R. (Eds.),Earth Processes: Reading the Isotopic Code, vol. 95, American Geophysical Union, Geophysical Monograph, pp. 207–231.

Davis, E.E., Karsten, J.L., 1986. On the cause of the asymmetric distribution of seamounts about the Juan de Fuca ridge:ridge-crest migration over a heterogeneous asthenosphere. Earth Planet. Sci. Lett. 79, 385–396.

Devey, C.W., Garbe-Schönberg, C.-D., Stoffers, P., Chauvel, C., Mertz, D.F., 1994. Geochemical effects of dynamic meltingbeneath ridges: reconciling major and trace element variations in Kolbeinsey (and global) mid-ocean ridge basalt. J. Geophys.Res. 99, 9077–9095.

Dittmer, F., Fine, S., Rasmussen, M., Bailey, J.C., Campsie, J., 1975. Dredged basalts from the mid-oceanic ridge north ofIceland. Nature 254, 298–301.

Eldholm, O., Skogseid, J., Sundvor, E., Myhre, A.M., 1990. The Norwegian-Greenland Sea. In: Grantz, A., Johnson, L., Sweeney,J.F. (Eds.), The Geology of North America, vol. L, The Arctic Ocean Region, Geol. Soc. Am., Boulder, 351–364.

Endres, Ch., 1992. Geochemie und Petrographie von Basalten des nordatlantischen Mittelozeanischen Rückens(Kolbeinsey-Rücken, Norwegisch-Grönländische See): Hinweise auf den Aufschmelzgrad. Unpublished Diploma thesis,Universität Kiel, 69 p.

Fitch, F.J., Grasty, R.L., Miller, J.A., 1965. Potassium-argon ages of rocks from Jan Mayen and an outline of its volcanic history.Nature 207, 1349–1351.

Fleck, R.J., Sutter, J.F., Elliot, D.H., 1977. Interpretation of discordant40Ar/39Ar spectra of Mesozoic tholeiites from Antarctica.Geochim. Cosmochim. Acta 41, 15–32.

Fontignie, D., Schilling, J.-G., 1991.87Sr/86Sr and REE variations along the Easter Microplate boundaries (south Pacific):Application of multivariate statistical analyses to ridge segmentation. Chem. Geol. 89, 209–241.

Furman, T., Frey, F., Park, K.-H., 1991. Chemical constraints on the petrogenesis of mildly alkaline lavas form Vestmannaeyjar,Iceland: the Eldfell and Surtsey (1963–1967) eruptions. Contrib. Mineral. Petrol. 109, 19–37.

Furman, T., Frey, F., Park, K.-H., 1995. The scale of source heterogeneity beneath the Eastern neovolcanic zone, Iceland. Geol.Soc. J. (London) 152, 997–1002.

Garbe-Schönberg, C.-D., 1993. Simultaneous determination of thirty-seven trace elements in twenty-eight international rockstandards by ICP-MS. Geostand. Newslett. 17, 81–97.


Grønlie, G., Chapman, M., Talwani, M., 1979. Jan Mayen Ridge und Iceland Plateau: origin and evolution. Norsk Polarinst.Skrifter 170, 25–47.

Haase, K.M., Devey, C.W., Mertz, D.F., Stoffers, P., Garbe-Schönberg, C.-D., 1996. Geochemistry of lavas from Mohns Ridge,Norwegian-Greenland Sea: Implications for melting conditions and magma sources near Jan Mayen. Contrib. Mineral. Petrol.123, 223–237.

Haase, K.M., Devey, C.W., Wieneke, M., 2003. Magmatic processes and mantle heterogeneity beneath the slow-spreadingnorthern Kolbeinsey Ridge segment. North Atlantic. Contrib. Mineral. Petrol. 144, 428–448.

Hanan, B.B., Schilling, J.-G., 1989. Easter Microplate evolution: Pb isotope evidence. J. Geophys. Res. 94, 7432–7448.Hanan, B.B., Schilling, J.-G., 1997. The dynamic evolution of the Iceland mantle plume: the lead isotope perspective. Earth

Planet. Sci. Lett. 151, 43–60.Hanan, B.B., Blichert-Toft, J., Kingsley, R., Schilling, J.-G., 2000. Depleted Iceland mantle plume geochemical signature: artifact

of multicomponent mixing? Geochem., Geophys., Geosyst., doi:1999G000009.Hards, V.L., Kempton, P.D., Thompson, R.N., 1995. The heterogeneous Iceland plume: new insights from the alkaline basalts

of the Snaefell volcanic centre. Geol. Soc. J. (London) 152, 1003–1009.Havskov, J., Atakan, K., 1991. Seismicity and volcanism of Jan Mayen Island. Terra Nova 3, 517–526.Hirose, K., Kawamoto, T., 1995. Hydrous partial melting of lherzolite at 1 GPa: the effect of H2H on the genesis of basaltic

magmas. Earth Planet. Sci. Lett. 133, 463–473.Hofmann, A.W., 1988. Chemical differentiation of the Earth: the relationship between mantle, continental crust, and oceanic

crust. Earth Planet. Sci. Lett. 90, 297–314.Imsland, P., 1980. The petrology of the volcanic Island Jan Mayen, Arctic Ocean. Nordic Volcanol. Inst. Iceland Internal

Rep. 8003, 134 p.Ito, G., Lin, J., Gable, C.W., 1996. Dynamics of mantle flow and melting at a ridge-centered hotspot: Iceland and the Mid-Atlantic

Ridge. Earth Planet. Sci. Lett. 144, 53–74.Ito, E., White, W.M., Göpel, C., 1987. The O, Sr, Nd and Pb isotope geochemistry of MORB. Chem. Geol. 62, 157–176.Jackson, E.D., Wright, T.L., 1970. Xenoliths in the Honolulu Volcanic Series. Hawaii. J. Petrol. 11, 405–430.Johnson, G.L., Campsie, J., 1976. Morphology and structure of the Western Jan Mayen Fracture Zone. Norsk. Polarinst. Arbok

1974, pp. 69–81.Karsten, J.L., Delaney, J.R., Rhodes, J.M., Liias, R.A., 1990. Spatial and temporal evolution of magmatic systems beneath the

Endeavour Segment Juan de Fuca Ridge: tectonic and petrologic constraints. J. Geophys. Res. 95, 19235–19256.Karsten, J.L., Hammond, S.R., Davis, E.E., Currie, R.G., 1986. Detailed geomorphology and neotectonics of the Endeavour

Segment, Juan de Fuca Ridge: new results from Seabeam swath mapping. Geol. Soc. Am. Bull. 97, 213–221.Klein, E.M., Langmuir, C.H., 1987. Global correlations of ocean ridge basalt chemistry with axial depth and crustal thickness.

J. Geophys. Res. 92, 8089–8115.Klingelhöfer, F., Géli, L., White, R.S., 2000. Geophysical and geochemical constraints on crustal accretion at the very-slow

spreading Mohns Ridge. Geophys. Res. Lett. 27, 1547–1550.Kodaira, S., Mjelde, R., Gunnarsson, K., Shiobara, H., Shimamura, H., 1997. Crustal structure of the Kolbeinsey Ridge, North

Atlantic, obtained by use of ocean bottom seismographs. J. Geophys. Res. 102 (B2,), 3131–3151.Lacasse, C., Paterne, M., Werner, R., Wallrabe-Adamas, H.-J., Sigurdsson, H., Carey, S., Pinte, G., 1996. Geochemistry and

origin of Pliocene and Pleistocene ash layers from the Iceland Plateau, Site 907. Proc. ODP Sci. Results 151, 309–329.Le Maitre, R.W., et al., 1989. A classification of igneous rocks and glossary of terms, Blackwell, Oxford, etc., 193 p.Maaløe, S., Sørensen, I.B., Hertogen, J., 1986. The trachybasaltic suite of Jan Mayen. J. Petrol. 27, 439–466.MacDonald, G.L., Katsura, T., 1964. Chemical composition of Hawaiian lavas. J. Petrol. 5, 83–133.Macpherson, C.G., Hilton, D.R., Mertz, D.F., Dunai, T., 1997. Tracing Plume, MORB, atmosphere contributions to Kolbeinsey

Ridge basalts: He, Ne, and Ar isotope evidence. In: Seventh V.M. Goldschmidt Conference, abstract vol., Tucson, pp. 129–130.Manhès, G., Minster, F.J., Allègre, C.J., 1978. Comparative uranium-thorium-lead and rubidium-strontium study of the Saint

Séverin Amphoterite: consequences for early solar system chronology. Earth Planet. Sci. Lett. 39, 14–24.McDougall, I., Green, D.H., 1964. Excess radiogenic argon in pyroxene and isotopic ages on minerals from Norwegian eclogites.

Norsk Geol. Tidss. 44, 183–196.Melson, W.G., O’Hearn, T., 1986. “Zero-age” variations in the composition of abyssal volcanic rocks along the axial zone of

the Mid-Atlantic Ridge. In: Vogt, P.R., Tucholke, B.E. (Eds.), The geology of North America, vol. M, The western NorthAtlantic region, Geol. Soc. Am., Boulder, pp. 117–136.


Mertz, D.F., Devey, C.W., Todt, W., Stoffers, P., Hofmann, A.W., 1991. Sr–Nd–Pb isotope evidence against plume-asthenospheremixing north of Iceland. Earth Planet. Sci. Lett. 107, 243–255.

Mertz, D.F., Haase, K.M., 1997. The radiogenic isotope composition of the high-latitude North Atlantic mantle. Geology 25,411–414.

Mertz, D.F., Renne, P.R., 1995. Quaternary multi-stage alkaline volcanism at Vesteris Seamount (Norwegian-Greenland Sea):evidence from laser step heating40Ar/39Ar experiments. J. Geodyn. 19, 79–95.

Michael, P., 1995. Regionally distinctive sources of depleted MORB: evidence from trace elements and H2O. Earth Planet. Sci.Lett. 131, 301–320.

Morgan W.J., 1981. Hotspot tracks and the opening of the Atlantic and Pacific Oceans. In: Emiliani, C. (Ed.), The Sea, vol. 7,pp. 443–487.

Morgan, W.J., 1983. Hotspot tracks and the early rifting of the Atlantic. Tectonophysics 94, 123–139.Myhre, A.M., Eldholm, O., Sundvor, E., 1984. The Jan Mayen Ridge: present status. Polar Res. 2, 47–59.Neumann, E.-R., Schilling, J.-G., 1984. Petrology of basalts from the Mohns-Knipovich Ridge; the Norwegian-Greenland Sea.

Contrib. Mineral. Petrol. 85, 209–223.Niu, Y., Bideau, D., Hékinian, R., Batiza, R., 2001. Mantle compositional control on the extent of mantle melting, crust production,

gravity anomaly, ridge morphology, and ridge segmentation: a case study at the Mid-Atlantic Ridge 33–35◦N. Earth Planet.Sci. Lett. 186, 383–399.

Niu, Y., Collerson, K.D., Batiza, R., Wendt, J.I., Regelous, M., 1999. Origin of enriched-type mid-ocean ridge basalt at ridgesfar from plumes: the East Pacific Rise at 11◦20′N. J. Geophys. Res. 104, 7067–7089.

Nunns, A., 1982. The structure and evolution of the Jan Mayen Ridge and surrounding regions. Am. Assoc. Petrol. Geol. Mem.34, 193–208.

Pedersen, S., Larsen, O., Hald, N., Campsie, J., Bailey, J.C., 1976. Strontium isotope and lithophile element values from thesubmarine Jan Mayen province. Geol. Soc. Denmark Bull. 25, 15–20.

Perry, R.K., 1986. Bathymetry. In: Hurdle, B.G. (Ed.), The Nordic Seas, Springer, New York, etc., pp. 211–233.Poreda, R., Schilling, J.-G., Craig, H., 1986. Helium and hydrogen isotopes in ocean-ridge basalts north and south of Iceland.

Earth Planet. Sci. Lett. 78, 1–17.Pringle, M.S., Staudigel, H., Gee, J., 1991. Jasper Seamount: seven million years of volcanism. Geology 19, 364–368.Renne, P.R., 1995. Excess40Ar in biotite and horneblende from the Norils’k 1 intrusion: Implications for the age of the Siberian

Traps. Earth Planet. Sci. Lett. 131, 165–176.Renne, P.R., Swisher, C.C., Deino, A.L., Karner, D.B., Owens, T.L., DePaolo, D.J., 1998. Intercalibration of standards, absolute

ages and uncertainties in40Ar/39Ar dating. Chem. Geol. 145, 117–152.Saemundsson, K., 1986. Subaerial volcanism in the western North Atlantic. In: Vogt, P.R., Tucholke, B.E. (Eds.),

The Geology of North America, vol. M, The western North Atlantic region, Geol. Soc. Am., Boulder, pp. 69–86.

Schwartzman, D.W., Giletti, B.J., 1977. Argon diffusion and absorption studies of pyroxenes from the Stillwater Complex.Montana. Contrib. Mineral. Petrol. 60, 143–159.

Schilling, J.-G., Zajac, M., Evans, R., Johnston, T., White, W., Devine, J.D., Kingsley, R., 1983. Petrologic and geochemicalvariations along the Mid-Atlantic Ridge from 29◦N to 73◦N. Am. J. Sci. 283, 510–586.

Schilling, J.-G., Kingsley, R., Fontignie, D., Poredda, R., Xue, S., 1999. Dispersion of the Jan Mayen and Iceland mantle plumesin the Arctic: A He–Pb–Nd–Sr isotope tracer study of basalts from the Kolbeinsey, Mohns, and Knipovich Ridges. J. Geophys.Res. 104, 10543–10569.

Sharp, W.D., Turrin, B.D., Renne, P.R., Lanphere, M.A., 1996.40Ar/39Ar and K–Ar dating of lavas from the Hilo 1-km coreholeHawaii Scientific Drilling Project. J. Geophys. Res. 101, 11607–11616.

Sigurdsson, H., 1981. First-order major element variation in basalt glasses from the Mid-Atlantic Ridge: 29◦N to 73◦N. J.Geophys. Res. 86, 9483–9502.

Smallwood, J.R., White, R.S., Minshull, T.A., 1995. Sea-floor spreading in the presence of the Iceland plume: the structure ofthe Reykjanes Ridge at 61◦40′N. Geol. Soc. J. (London) 152, 1023–1029.

Stecher, O., Carlson, R., Gunnarsson, B., 1999. Torfajökull: a radiogenic end-member of the Iceland Pb-isotopic array. EarthPlanet. Sci. Lett. 165, 117–127.

Steiger, R.H., Jäger, E., 1977. Subcommission on geochronology: convention on the use of decay constants in geo- and cos-mochronology. Earth Planet. Sci. Lett. 36, 359–362.


Stolper, E., Newman, S., 1994. The role of water in the petrogenesis of Mariana trough magmas. Earth Planet. Sci. Lett. 121,293–325.

Sun, S.-S., Nesbitt, R.W., Sharaskin, A.Y., 1979. Geochemical characteristics of mid-ocean ridge basalts. Earth Planet. Sci. Lett.44, 119–138.

Sun, S.-S., McDonough, W.F., Chemical and isotope systematics of oceanic basalts: implications for mantle composition andprocesses. In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in the Ocean Basins, vol. 42 Geological Society (London)Spec. Publ., 1989, pp. 313–345

Talwani, M., Eldholm, O., 1977. Evolution of the Norwegian-Greenland Sea. Geol. Soc. Am. Bull. 88, 969–999.Thirlwall, M.F., 1995. Generation of the Pb isotopic characteristics of the Iceland plume. Geol. Soc. J. (London) 152, 991–996.Thirlwall, M.F., Upton, B.G.J., Jenkins, C., 1994. Interaction between continental lithosphere and the Iceland plume–Sr–Nd–Pb

isotope geochemistry of Tertiary basalts. NE Greenland. J. Petrol. 35, 839–879.Torske, T., Prestvik, T., 1991. Mesozoic detachment faulting between Greenland and Norway: inferences from Jan Mayen

Fracture Zone system and associated alkalic volcanic rocks. Geology 19, 481–484.Trønnes, R., Planke, S., Sundvoll, B., Imsland, P., 1999. Recent volcanic rocks from Jan Mayen: low degree melt fractions of

enriched northeast Atlantic mantle. J. Geophys. Res. 104, 7153–7167.Upton, B.G.J., Emeleus, C.H., Beckinsale, R.D., Macintyre, R.M., 1984. Myggbukta and Kap Broer Ruys: the most northerly

of the East Greenland Tertiary igneous centres. Mineral. Mag. 48, 323–343.Upton, B.G.J., Emeleus, C.H., Rex, D.C., Thirlwall, M.F., 1995. Early Tertiary magmatism in NE Greenland. Geol. Soc. J.

(London) 152, 959–964.Verma, S.P., Schilling, J.-G., Waggoner, D.G., 1983. Neodymium isotopic evidence for Galapagos hotspot-spreading centre

system evolution. Nature 306, 654–657.Vink, G.E., 1984. A hotspot model for Iceland and the Vøring Plateau. J. Geophys. Res. 89, 9949–9959.Vogt, P.R., 1971. Asthenosphere motion recorded by the ocean floor south of Iceland. Earth Planet. Sci. Lett. 13, 153–160.Vogt, P.R., 1986. Geophysical and geochemical signatures and plate tectonics. In: Hurdle, B.G. (Ed.), The Nordic Seas, vol.

413–662. Springer, New York, etc.Waggoner, D.G., 1989. An isotopic and trace element study of mantle heterogeneity beneath the Norwegian-Greenland Sea.

Unpublished PhD Thesis, University of Rhode Island, 154 p.Yale, M.M., Phipps Morgan, J., 1998. Asthenophere flow model of hotspot-ridge interactions: a comparison of Iceland and

Kerguelen. Earth Planet. Sci. Lett. 161, 45–56.Zhang, Y.-S., Tanimoto, T., 1992. Ridges, hotspots, and their interaction as observed on seismic velocity maps. Nature 355,

45–49.

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