Abstract
We review the compositional variation of eudialyte-group minerals (EGM) from the Ilímaussaq complex in South Greenland. Investigated samples cover all major rock units and associated pegmatites and aplites. The whole data set (>3000 analyses from >250 samples) exhibits variable XMn (0.1–0.5), REE (0.2–1.7 apfu), Nb (0.1–0.4), and Cl contents (0.4–1.6 apfu). Most EGM compositions are Na-rich (13–15 apfu), while deviations to Na-rich but also to Na-poor compositions occur because of a combination of primary features (peralkalinity, water activity) and secondary alteration. During magma evolution, REE contents in EGM cores generally increase and reach their highest contents in the most evolved rock units of the complex. This points to the moderate compatibility of REE in EGM and a bulk D (cEGM/cmelt) value of <1 during magma differentiation. Chlorine contents in EGM cores continuously decrease, and are lowest at the rims of individual crystals, suggesting a continuous decrease of Cl activity in the magmas by large-scale EGM and sodalite extraction during the orthomagmatic stage and water enrichment during the late-magmatic stage. The overall variations of XMn across stratigraphy are only minor and likely influenced by the co-crystallization of sodic pyroxene and amphibole (c.f. aegirine, arfvedsonite) and local phase proportions. Similarly, Nb and Ti contents are influenced by co-crystallizing aenigmatite, rinkite, and others. Their presence buffers Ti and Nb contents to rather constant and low values, while their absence may cause variable enrichment on a local scale. Very low Sr contents (<0.1 apfu) in magmatic EGM from Ilímaussaq are related to the basaltic nature of the parental magmas of the complex, as large-scale plagioclase fractionation occurred prior to the formation of the Ilímaussaq magmas, effectively removing Sr from the system. This is in line with very strong negative Eu anomalies in EGM from Ilímaussaq. Consistently, Sr contents in EGM from alkaline complexes, for which foiditic parental magmas are assumed, are much higher and, in such cases, negative Eu anomalies are generally absent.
Highlights
Minerals of the eudialyte-group (EGM) are a complex group of mostly Na- and Ca-rich Zr-silicates with variable amounts of K, Sr, Fe, Mn REE, Y, Nb, Ti, and other elements
They mostly occur in pegmatites or late-stage dyke rocks that crosscut otherwise miaskitic rocks (e.g., Magnet Cove, Kovdor, Dara-i-Pioz) or as interstitial phases dispersed in spatially restricted areas of otherwise miaskitic rocks (e.g., Tamazeght, Pilanesberg, Junguni)
Large data sets that document the compositional variation of eudialyte-group minerals (EGM) from Ilímaussaq have been presented by several authors [9,10,20,21,22,35], all focusing on rocks that constitute the floor and intermediate sections
Summary
Minerals of the eudialyte-group (EGM) are a complex group of mostly Na- and Ca-rich Zr-silicates with variable amounts of K, Sr, Fe, Mn REE, Y, Nb, Ti, and other elements. Members of the eudialyte-group are known from roughly 100 localities worldwide, defining so-called agpaitic rocks, as recently reviewed by [1] They mostly occur in pegmatites or late-stage dyke rocks that crosscut otherwise miaskitic rocks (e.g., Magnet Cove, Kovdor, Dara-i-Pioz) or as interstitial phases dispersed in spatially restricted areas of otherwise miaskitic rocks (e.g., Tamazeght, Pilanesberg, Junguni). These occurrences show large differences in terms of areal extent and abundance of EGM-bearing dyke rocks. A comparison is made to EGM compositions from several other key localities and we show that the general EGM chemistry at a given locality can be used to characterize the nature of parental magma and fluid sources, depending on the relative timing of EGM formation (early magmatic, late magmatic, hydrothermal)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
