The Tertiary Kærven Syenite Complex, Kangerdlugssuaq, East Greenland: Mineral Chemistry and Geochemistry

Abstract

The K~erven syenite complex, which reflects the hitherto earliest recorded stages in the Tertiary of East Greenland, outcrops in the middle reaches of the Kangerdlugssuaq Fjord as a peripheral intrusion to the Kangerdlugssuaq intrusion. The rocks of the K~erven complex range from syenite through alkali feldspar quartz-syenite to alkali feldspar granite. The general sequence of crystallization of the K~erven magmas was: alkali feldspar + olivine(Fa96_99 ) + plagioclase(An41_10, clinopyroxene (augite, ferrosalite, ferrohedenbergite), quartz and amphibole. Whole-rock major and trace-element data show coherent geochemical trends which suggest comagmatism. The data reveal that the K~erven rocks are distinct from the rocks from the adjacent Kangerdlugssuaq intrusion (e.g. higher TiO2, FeO T in low-SiO z samples, lower Na20 , approx, constant Zr/Nb). The mineral chemistry supports this conclusion, as the K~erven samples typically have calcic amphiboles and clinopyroxenes with a very limited Na-enrichment in contrast to the sodic trends of the Kangerdlugssuaq intrusion. Normative feldspar compositions plot near to the Ab-Or cotectic in the Q-Ab-Or system and a maximum pressure of crystallization of 3-5 kbar with moderate to low Pn~o is indicated.Trace elements preferently incorporated in plagioclase and alkali feldspar, i.e. Sr, Ba and Rb, show systematics which are not compatible with an evolution of the rock suite by crystal fractionation of these phases, though possibly alkali feldspar may be partially accumulated in a few very evolved rocks. Numerical calculations do not suggest a magmatic evolution by fractional crystallization of the observed phases. The variation of Sr, Ba and Rb as well as of the incompatible elements Nb, Zr and Th support a derivation of the rock suite mainly by mixing two components, a syenitic and a granitic end-member. It is concluded that magma mixing was the most significant process in the formation of the Kzerven rock suite accompanied by some crystal fractionation. Evidence for crustal contamination is detected in a few samples from the outer part of the intrusion but has not affected the main suite of rocks.

Comments on ‘The Tertiary Kærven syenite complex, Kangerdlugssuaq, East Greenland: mineral chemistry and geochemistry’ by P. M. Holm and N.-O. Prægel

“…Accordingly, it is concluded that: (a) At least two groups of syenites and granites occur at Kaerven and as no single coherent trend is shown they may not be comagmatic. (b) The major mineralogical and chemical differences which are claimed between all the syenites and granites of the K~erven syenite complex and the Kangerdlugssuaq intrusion and other satellite intrusions are not shown by the chemical data in Holm and Pr~egel's paper, nor by the presented mineralogical observations of Holm andPr~egel (1988}~i~r Deer andKempe (1976). Some groups of rocks appear common to all the intrusions.…”

“…IN a recent paper Holm and Pr~egel (1988) have described the syenites and alkaline granites of the K~erven syenite complex from the lower Tertiary magmatic province of East Greenland. The province developed during the early stages of the opening in the North Atlantic (e.g.…”

(Presidential Address 1993) Demise of the dinosaurs and other denizens II – by combined catastrophic causes?

“…The Greenland plume is equated with major North Atlantic doming and uplift at 65£5Ma prior to rifting and extensive volcanism after 63Ma (White and McKenzie, 1989;Hill, 1991;Lewis et al, 1992). A proposed starting plume generated melts over an area 2,500km in diameter and passed southwards where 58Ma syenite of hotspot character is intruded near Kaerven (Holm and Praegel, 1988) and massive volcanism and spreading took place 200kms further south (White, 1993). The K/T plume position may be marked by intense alkali dolerite dyke injection and bimodal basaltic and alkaline volcanism (64+3Ma) in northern Greenland (Kap Washington Volcanics) (Brown et al, 1987).…”