Interaction between Continental Lithosphere and the Iceland Plume--Sr-Nd-Pb Isotope Geochemistry of Tertiary Basalts, NE Greenland

• Published in: Journal of Petrology
• Main Authors: THIRLWALL, M. F., UPTON, B. G. J., JENKINS, C.
• Format: Text
• Language: English
• Published: Oxford University Press 1994
• Subjects: Articles; Greenland; Wollaston; Wollaston Forland; Hold with Hope; East Greenland; Iceland; Wollaston forland
• Online Access: http://petrology.oxfordjournals.org/cgi/content/short/35/3/839; https://doi.org/10.1093/petrology/35.3.839

Volcanic rocks associated with Atlantic opening in northern east Greenland (73–76°N) form a ∼1-km thickness of basaltic lavas located on the coast some 400 km north of the major basalt accumulations of the Blosseville Coast (<70°N). The Lower Lava Series, which makes up the lower half of the sequence at Hold with Hope and all of that at Wollaston Forland, is composed of homogeneous quartz tholeiites (5–8% MgO). These are mildly light rare earth element (LREE) enriched (La/Yb N 2.06±0.45, 1 S.D.) and show strong chemical and Pb-Nd-Sr isotopic similarities to Icelandic tholeiites. They are distinguished from Atlantic mid-ocean ridge basalt (MORB) in having less radiogenic Pb and Nd, higher Δ8/4 and lower Δ7/4, and depletion in K and Rb relative to other incompatible elements, and show no evidence of a MORB asthenosphere component in their source. A single nephelinite in the Lower Series has essentially similar isotopic characteristics and K, Rb depletion. The tholeiites were derived from the hot head of the Iceland plume, which had spread laterally within the upper mantle, and represent large melt fractions (15–20%) from spinel-facies mantle combined with small melt fractions (∼2.2%) from the garnet facies. Pb isotopic data indicate that the Iceland plume contains no MORB asthenospheric component, and is therefore most unlikely to arise from enriched streaks in the convecting upper mantle. The K, Rb depletion is shared with the HIMU ocean islands, and suggests a similar origin for the Iceland plume in subduction-processed oceanic crust. The relatively low 206Pb/204Pb ratios, and near-MORB Sr-Nd isotopes, suggest that Iceland overlies an immature HIMU plume. The conformably overlying upper half of the Hold with Hope sequence (the Upper Lava Series) is extremely heterogeneous, being mainly olivine and quartz tholeiites (4.5–9.5% MgO in inferred melt compositions, and up to 27% in accumulative lavas), with occasional undersaturated compositions. The latter are concentrated near the base of the Upper Series, and ...