The Prinsen af Wales Bjerge Formation Lavas, East Greenland: the Transition from Tholeiitic to Alkalic Magmatism during Palaeogene Continental Break-up

Abstract

thick lithospheric cap, with 3 He contributed from volatile-rich fluids We present elemental and isotopic (Sr-Nd-Pb-Hf-Os-He) data from elsewhere in the Icelandic plume. The exact nature of the recycled on primitive alkalic lavas from the Prinsen af Wales Bjerge, component is not yet resolved, although Hf isotope compositions rule East Greenland. Stratigraphical, compositional and 40 Ar-39 Ar data out any significant role for recycled pelagic sediment, and the low indicate that this inland alkalic activity was contemporaneous with 187 Os/ 188 Os limits the participation of recycled basaltic material the upper parts of the main tholeiitic plateau basalts and also postand argues instead for a contribution from the mantle section of the dated them. The alkalic rocks show a marked crustal influence, recycled slab. indicating establishment of new magmatic plumbing systems distinct from the long-lived coastal systems that fed the relatively uncontaminated plateau basalts. The least contaminated lavas have high 3 He/ 4 He isotope ratios (R/R A 12•4-18•5), sub-chondritic 187 Os/ 188 Os i (0•120-0•126), low Nd i (>+4) and Hf i KEY WORDS: alkalic lavas; flood basalts; high 3 He/ 4 He; East Greenland; (>+6) that plot below the 'Nd-Hf mantle array', and trace recycled lithosphere; Iceland plume element characteristics similar to HIMU ocean island basalt (OIB). The uncontaminated magma is inferred to have more radiogenic 206 Pb/ 204 Pb values (>19•2) than the plateau basalts and Icelandic basalts, and thus represents a possible 'enriched' component to

High-3He/4He, depleted mantle and low-δ18O, recycled oceanic lithosphere in the source of central Iceland magmatism

“…While the most enriched lava (NAL-625) has higher La/Yb and Sm/Yb than the glasses, it more closely resembles Group 1 than Group 2 in having progressive relative depletion of elements more incompatible than Nb. Province [24][25][26] except for Baffin Island picrites [27]. The 3 He/ 4 He ratio of this sample is also similar to rocks from Loihi Seamount, Hawaii, and the Galapagos islands, the only other modern day ocean islands to register helium isotope ratios greater than 25R A [28][29][30][31].…”

Hot and Heterogenous High‐3He/4He Components: New Constraints From Proto‐Iceland Plume Lavas From Baffin Island

“…Crustal contamination is recorded in high‐ 3 He/ 4 He continental flood basalts associated with the Icelandic plume at Baffin Island, West Greenland, and East Greenland (e.g., Day, ; Larsen & Pedersen, ; Lightfoot et al, ; Peate, ; Yaxley et al, ). If the Iceland hotspot has a single high‐ 3 He/ 4 He component, one hypothesis is that the high‐ 3 He/ 4 He mantle component sampled at the Iceland hotspot has a single Sr‐Nd‐Hf‐Pb isotopic composition over time and that the difference in Sr‐Nd‐Hf‐Pb between Iceland and the least contaminated Baffin Island high‐ 3 He/ 4 He lavas is due to melts of the latter having assimilated some amount of continental crust.…”

“…Crustal contamination is recorded in high-3 He/ 4 He continental flood basalts associated with the Icelandic plume at Baffin Island, West Greenland, and East Greenland (e.g., Day, 2016;Larsen & Pedersen, 2009;Lightfoot et al, 1997;Peate, 2003;Yaxley et al, 2004) Hilton et al, 1999). The shift to lower 87 Sr/ 86 Sr in the least contaminated, highest 3 He/ 4 He Baffin Island lava cannot be explained by continental crust assimilation because assimilation of the local Precambrian crust (which has very high 87 Sr/ 86 Sr-0.713758 to 0.823010-compared to the least crustally contaminated Baffin Island lavas, 0.703008 to 0.703021) would only serve to increase the Baffin Island 87 Sr/ 86 Sr, not decrease it (Figure 8).…”

Nitrogen isotopes of the mantle: Insights from mineral separates

“…N 2 /Ar and 40 Ar/ 36 Ar were analyzed on the same gas using the VG3600. Helium isotopes of olivine separates were analyzed at Scripps Institution of Oceanography following the techniques described by Peate et al [2003]. Helium and Ar isotopes of some samples were analyzed in the Laboratory for Earthquake Chemistry, University of Tokyo following the techniques of Sumino et al [2001].…”