Post-breakup basaltic magmatism along the East Greenland Tertiary rifted margin

被引:41
作者
Bernstein, S
Kelemen, PB
Tegner, C
Kurz, MD
Blusztajn, J
Brooks, CK
机构
[1] Danish Lithosphere Ctr, DK-1350 Copenhagen K, Denmark
[2] Woods Hole Oceanog Inst, Woods Hole, MA 02543 USA
[3] Univ Copenhagen, Inst Geol, DK-1350 Copenhagen K, Denmark
关键词
basalts; igneous activity; continental drift; East Greenland; continental margin; Tertiary;
D O I
10.1016/S0012-821X(98)00132-0
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Mafic and ultramafic intrusions in East Greenland adjacent to the offshore Greenland-Iceland ridge were emplaced 5-9 My after continental breakup at 55 Ma [1], Rare earth element (REE) concentrations determined by secondary ion mass spectrometry are reported for cumulus clinopyroxene from these intrusions, and the data are used to estimate REE abundance in equilibrium melts using available partitioning data. Estimated equilibrium melts from intrusions have strongly fractionated REE patterns with Nd/Dy(N) in the range 2 to 5.6 and Yb/Dy(N) 0.55 to 0.92, similar to values for coeval basalts, These melts have markedly higher Nd/Dy(N) than earlier breakup related flood basalts, The moderately low Yb/Dy(N) for the post-breakup volcanism is indicative of residual garnet in the source, while their high Nd/Dy(N) ratios can best be explained by aggregating low degree melts from a light-REE-enriched garnet- and spinel-bearing mantle source. We also report He, Sr, and Nd isotopic data for the intrusions. The highest He-3/He-4 ratios (>10 R/R-a) are found in the samples whose REE data reflect the largest proportion of melts from a garnet-bearing source, and having Sr and Nd isotopic compositions identical with the radiogenic Sr and unradiogenic Nd isotope end of the Iceland compositional field. There is no indication of a MORE-type mantle in the source of the intrusions. We postulate that post-breakup volcanism along the East Greenland coastline reflects the increasing proximity of the mantle plume to the East Greenland continental margin, The low degree of melting at high mean pressure inferred for the parental melts for the intrusions may reflect re-thickening of the lithosphere, which in turn was caused by the vigorous volcanism during breakup, with accompanying depletion of upper mantle and underplating of the crust at the continental margin. (C) 1998 Elsevier Science B.V. All rights reserved.
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页码:845 / 862
页数:18
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