The Prinsen af Wales Bjerge formation lavas, East Greenland: The transition from tholeiitic to alkalic magmatism during Palaeogene continental break-up
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 plate...
| Published in: | Journal of Petrology |
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| Main Authors: | , , , , , , , , , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford Univ Press
2003
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| Subjects: | |
| Online Access: | https://doi.org/10.1093/petrology/44.2.279 https://archimer.ifremer.fr/doc/00224/33507/31953.pdf https://archimer.ifremer.fr/doc/00224/33507/ |
| Summary: | 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. |
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