THE NORTH ATLANTIC IGNEOUS PROVINCE
Melilitites in North-East Greenland: samples of fused recycled oceanic lithosphere

Stefan Bernstein, in collaboration with Rikke Harlou (Univ. Durham, UK), Ole Stecher, Joel Baker and David Ulfbeck (Danish Lithosphere Centre), Karen Hanghøj and Mark Kurz (Woods Hole Oceanog. Institution).

The research on the NE Greenland melilitites is model-driven: we aim at providing the first description of the melt component derived directly from recycled oceanic lithosphere. The chemistry of the melilitites suggests that they were formed by low degree ( <5%) melting at pressures at 7 gpa of ca. 2.7 ga old, recycled oceanic lithosphere (bernstein et al., 2003).
the mantle sources of hot-spot magmatism are intensely and widely debated, and our work on ne greenland lavas supports the group of scientists who argue for the importance of large-scale recycling of the oceanic lithosphere. however, modelling of mantle melting in hot-spot regimes has hitherto been focussed on the behaviour of a simple one-component source chemistry (e. g. mckenzie & o'nions, 1995). the enriched compositions of hot-spot magmas, both on continents and in the ocean basins, have been explained in terms of higer average pressure of melting compared to normal mid-ocean ridge magmatism. our work provides strong evidence that the basic assumptions for the more traditional approach to the modelling of mantle melting above hot-spots are incorrect.
While several workers have advocated for the existence of recycled oceanic lithosphere in the source of hot-spot magmatism, the evidence have always been indirect - with the introduction of a hypothetical endmember representing some of the chemical characteristics of the studied lava samples.
Our work presents the first direct evidence that this endmember may actually be found as a distinct volcanic product, namely the NE Greenland alkaline lavas.

Publications
Bernstein, S., Stecher, O. Ulfbeck, D., Harlou, R., Baker, J., & Kurz, M. D. 2003: Melts derived directly from recycled oceanic lithosphere - an example from NE Greenland volcanics. EUG/EGS/AGU joint assembly, Nice, France.

Bernstein, S., Brooks, C.K., and Stecher, O., 2001: Enriched component of the proto-Icelandic mantle plume revealed in alkaline Tertiary lavas from East Greenland. Geology. 29, 859–862.

Bernstein, S., Leslie, A.G., Higgins, A.K., and Brooks, C.K., 2000. Tertiary alkaline basic volcanics in the Nunatak Region, North-East Greenland: new discoveries and their similarities to the maymechites of Siberia. Lithos 53, 1–20.

Figure texts 1. Nunatak Region lavas occur as thin caps (10–150 m thick) on peneplained Proterozoic metasediments in Northeast Greenland. Height of cliff is about 500 m. 2. Hf and Nd isotope compositions of the Nunatak lavas suggest that they are derived from a mantle source which has seen an ancient depletion in light rare earth elements and in Hf relative to Lu. This is compatible with an origin as partial melts of recycled Archaean MORB or komatiites.