Contrasts in composition and evolution of Tertiary CFBs between West and East Greenland and their relations to the establishment of the Icelandic mantle plume

Abstract

Abstract In the West Greenland CFB Province, the early lava compositions were dominated by tholeiitic picrites more depleted in terms of isotopic and trace element characteristics than CFBs from any other province, and comparable to those of present-day Icelandic lavas. Later basalts have similar isotopic and incompatible element ratios. Generally, the West Greenland CFBs show no significant interaction with the lithosphere. In East Greenland, the early picrites and basalts from the Kangerlussuaq area have a very wide range of compositions, which strongly indicate lithospheric interaction. The Scoresby Sund basalts, as well as later basalts in the Kangerlussuaq area, have much less variable compositions, and are similar to the most enriched modern Icelandic picrites. The difference between the early West and East Greenland volcanic rocks is probably related to differences in tectonic setting. In West Greenland continental rifting started before volcanism on the continental margin. The arrival of the proto-Icelandic plume material made primitive picritic magma rise quickly through the already rifted lithosphere. In East Greenland no rifting took place until c. 4 Ma after the arrival of plume material under West Greenland. This allowed small amounts of plume-derived melts to enter and react with the lithosphere and subsequently be incorporated into the CFB magmas at the rifting stage. No thermal doming took place in East Greenland before or during continental break-up, and the East Greenland rifting is considered to have been passive. Very high temperatures and high degrees of melting during picrite generation in East Greenland is a strong indication that the plume was centred under Kangerlugssuaq at the time of rifting. The vigorous interaction between early magmas and lithosphere makes it likely that the plume was centred here also for the 4 Ma prior to rifting.