Geochemical and isotopic studies of the tertiary volcanic rocks from the Blosseville coast region, East Greenland
The Lower Tertiary volcanic sequence of the Blosseville Coast region was erupted in a 3 m.y. period immediately prior to the initiation of sea floor spreading in the adjacent part of the North Atlantic. This volcanic province is comprised of a major flood basalt sequence (the Plateau Lavas), the eruption of which was preceded by localised basaltic volcanism (the Lower Lavas) and succeeded by eruptive activity which produced minor volcanic cones.The Lower Lavas and Plateau Lavas comprise the Blosseville Group and these volcanics are entirely tholeiitic in character. The evolution of these lavas can be described in terms of their derivation from mantle sources of limited isotopic and chemical variability. Bulk contamination of these magmas has generated additional isotopic variability though indicating minimal contamination in the majority of cases. The major and trace element compositional diversity amongst these magmas was controlled by a fractionation process involving olivine, clinopyroxene and plagioclase.Two magmatic types are present amongst the Nunatak Group lavas. These volcanics are predominantly alkaline in character and comprise a series of petrographic types which were generatedby low pressure fractionation of picritic parents. These alkaline types were derived from mantle sources with considerable trace element and isotopic variability. The tholeiitic magmas of the Nunatak Group are intimately related to those of the Blosseville Group.It is suggested that the tholeiitic magmas of the region represent the initial establishment of the Icelandic hotspot in the early Tertiary. This magmatic activity has tapped similarmantle sources throughout its history. The alkaline magmas were dervied from fundamentally different mantle sources and are probably generated through tectonic/thermal disturbance of the sub-continental mantle.