Palaeogene Continental to Oceanic Magmatism on the SE Greenland Continental Margin at 63°N: a Review of the Results of Ocean Drilling Program Legs 152 and 163

Abstract

mantle melting zone, accompanied by an increase in the average Drilling along a 63°N transect off SE Greenland during Ocean degree of melting with time from >4% to >12%. These modest Drilling Program (ODP) Legs 152 and 163 recovered a succession degrees of melting imply mantle temperatures only >100°C hotter of volcanic rocks representing all stages in the break-up of the than normal upper mantle. Upwelling mantle must therefore have volcanic rifted margin. The rocks range from pre-break-up continental been fed dynamically to the melt zone to generate the igneous crust tholeiitic flood basalt, through syn-break-up picrite, to truly oceanic of 18 km thickness deduced from seismic and gravity studies. Nbasalt forming the main part of the seaward-dipping reflector MORB-like magmas dominated the earliest part of the succession sequence (SDRS). All the lava flows recovered from the transect although a few flows of ‘Icelandic’ basalt were erupted in the prewere erupted in a subaerial environment. Ar–Ar dating shows break-up phase. In contrast, the post-break-up magmas had an that the earliest magmas were erupted at >61 Ma and has Icelandic mantle source. This suggests that the developing head of confirmed that the main part of the SDRS was erupted during C24r the ancestral Iceland plume was compositionally zoned, with a core (56–53 Ma) following continental break-up. Magma represented by of Icelandic mantle surrounded by a thick outer zone of hot, depleted the pre-break-up lava flows was stored in crustal reservoirs where upper mantle. it evolved by fractional crystallization and assimilation of continental crust. Trace element and radiogenic isotope data show that the contaminant changed, through time, from lower-crustal granulite to a mixture of granulite and amphibolite, suggesting storage of magma at progressively shallower levels in the crust. The degree of contamination declined rapidly as break-up proceeded, and the youngest rocks sampled in the transect are uncontaminated by continental basement. Variation of, for example, Sc/Zr and Sm/