The Prinsen af Wales Bjerge formation lavas, East Greenland: The transition from tholeiitic to alkalic magmatism during Palaeogene continental break-up
|Author(s)||Peate Dw1, Baker Ja1, Blichert-Toft J2, Hilton Dr3, Storey M1, Kent Ajr1, Brooks Ck1, 4, Hansen' H1, Pedersen Ak1, 5, Duncan Ra6|
|Affiliation(s)||1 : Danish Lithosphere Ctr, DK-1350 Copenhagen K, Denmark.
2 : Ecole Normale Super Lyon, Lab Sci Terre, F-69364 Lyon, France.
3 : Univ Calif San Diego, Scripps Inst Oceanog, Geosci Res Div, La Jolla, CA 92093 USA.
4 : Univ Copenhagen, Inst Geol, DK-1350 Copenhagen K, Denmark.
5 : Geol Museum, DK-1350 Copenhagen K, Denmark.
6 : Oregon State Univ, Coll Ocean & Atmospher Sci, Corvallis, OR 97331 USA.
|Source||Journal Of Petrology (0022-3530) (Oxford Univ Press), 2003-02 , Vol. 44 , N. 2 , P. 279-304|
|WOS© Times Cited||59|
|Keyword(s)||alkalic lavas, flood basalts, high He-3/He-4, East Greenland, recycled lithosphere, Iceland plume|
|Abstract||We present elemental and isotopic (Sr-Nd-Pb-Hf-Os-He) data on primitive alkalic lavas from the Prinsen af Wales Bjeige, East Greenland. Stratigraphical, compositional and Ar-40-Ar-39 data indicate that this inland alkalic activity was contemporaneous with the upper parts of the main tholeiitic plateau basalts and also postdated them. The alkalic rocks show a marked crustal influence, 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 He-3/He-4 isotope ratios (R/R-A 12.4-18.5), sub-chondritic Os-187/(OSi)-O-88 (0.120-0.126), low epsilonNd(i) (similar to + 4) and epsilonHf(i) (similar to+ 6) that plot below the 'Nd-Hf mantle array', and trace element characteristics similar to HIMU ocean. island basalt. (OIB). The uncontaminated magma is inferred to have more radiogenic Pb-206/Pb-204 values (>19.2) than the plateau basalts and Icelandic basalts, and thus represents a possible 'enriched' component to explain the compositional variations within the plateau basalts. One model to explain these compositional features is preferential melting of recycled material within the plume upwelling beneath the thick lithospheric cap, with He-3 contributed from volatile-rich fluids from elsewhere in the Icelandic plume. The exact nature of the recycled component is not yet resolved, although Hf isotope compositions rule out any significant role for recycled pelagic sediment, and the low Os-187/Os-188 limits the participation of recycled basaltic material and argues instead for a contribution from the mantle section of the recycled slab.|