Metasomatism in the North Qôroq centre, South Greenland: apatite chemistry and rare-earth element transport

Abstract

The North Q6roq syenite centre forms part of the Gardar Province of South Greenland. Extensive metasomatism, associated with the evolution of syenitic magmas, has resulted in redistribution of the rareearth elements (REE), originally concentrated by magmatic processes, in both the syenites and surrounding granite-gneiss and quartzite country rocks. An important host for REE is apatite which can occur irl significant quantities. Metasomatic apatites show complex, concentric, but irregular patterns of zonation, clearly seen using CL and BSE imaging. This zonation is related to successive pulses of metasomatising fluids. Electron microprobe analysis confirms the presence of significant quantities of REE in the apatites. The dominantcation exchange mechanism proposed is Ca + P ~--~ REE + Si . In contrast to apatites from the nearby Ilfmaussaq intrusion, there is no significant Na present in the structure and exchange reactions involving Na + and REE 3+ for Ca 2+ have not occurred. Apatites from the quartzite are fluor-apatites, while those from the granite-gneiss are more Cl-rich. These differences reflect the fact that granite-gneiss apatites are original and modified by metasomatism, whereas, those in the quartzite are metasomatic in origin. REE were probably transported as carbonate, fluoride or fluor-carbonate complexes, and reflect the activity of a F-rich, CO~ -rich fluid phase.

The Fazenda Largo off-craton kimberlites of Piauí State, Brazil

“…An assessment of the specific behaviour of different trace elements, in the rocks being studied, must be performed taking into account their very different mobilities in metasomatic and hypergene rock transformation processes (e.g., Rae et al, 1996).…”

The Compositional Evolution of Apatite in the Weathering Profile of the Catalao I Alkaline-Carbonatitic Complex, Goias, Brazil

“…The majority of the bibliographic references mentioned here use the double formula for the apatite [A 10 X 6 Y 2 ], and the same will be done here, to simplify comparisons. Various ways of calculating a structural formula for apatite have been presented in the literature: a) on the basis of the total number of oxygen atoms or anionic content (Roeder et al 1987, Treloar & Colley 1996, Rønsbo 1989, Rae et al 1996, b) on the basis of cationic sum at the A position plus the cation sum at the X or phosphorus position (Fleet & Pan 1995, Prins 1973, c) on the basis of the sum of ions at the X position (Fransolet & Schreyer 1981), and d) on the basis of number of cations in position A (Le Bas & Handley 1979, Sommerauer & Katz-Lehnert 1985, Liu & Comodi 1993.…”

Evolution of the North Qôroq centre nepheline syenites, South Greenland: alkali-mafic silicates and the role of metasomatism

“…1). It is cut by a number of basic to evolved dykes, and two small brecciated diatremes of carbonatitic af nity (Coulson, 1996;Coulson et al, 1998Coulson et al, , 2003. Pegmatites are fairly common throughout the centre.…”

“…Extensive in situ fractional crystallization has been postulated for the extensive chemical variation exhibited both within units and throughout the centre (Chambers, 1976). Metasomatism, associated with reactive uids, generated by the repeated intrusion of younger syenite (Rae and Chambers, 1988;Rae et al, 1996;Coulson and Chambers, 1996), has produced a variety of metasomatized syenites and country rocks.…”