Interpretation of field observations in the southern part of the Ilímaussaq intrusion, South Greenland

Demin, A

doi:10.34194/rapggu.v45.7294

Cited by 2 publications

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“…The kakortokite section northwest of Lakseelv is relatively well exposed and was measured and described by Demina (1971Demina ( , 1972Demina ( , 1979. The most detailed description of the section from 1979 was never published.…”

Section: The Kakortokite Sequence Northwest Of Lakseelvmentioning

confidence: 99%

Assimilation and extensive metasomatism of agpaitic rocks from the transitional layered kakortokite, Ilímaussaq Intrusion, South Greenland

Schønwandt,

Barnes,

Ulrich

2023

Resource Geology

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The peralkaline Ilímaussaq Intrusion of the Gardar Province in South Greenland consists of several intrusive phases that have been related to different magmatic pulses and igneous cumulate processes. The lowermost exposed part of the intrusion is kakortokite, a eudialyte‐nepheline syenite, with distinctive sub‐horizontal layering which passes upwards into lujavrite, a fine‐grained melanocratic eudialyte‐nepheline syenite. Along the contact between kakortokite and lujavrite lies a transitional layered kakortokite, which has been defined previously based on textural and mineralogical criteria. However, published literature presents conflicting descriptions of this sequence in terms of thickness, layering, contacts, and mode of origin. Our own and previous field and petrographic investigations suggest that parts of the eudialyte‐rich zones in the transitional layered kakortokite comprise metasomatized and partially assimilated naujaite autoliths, a sodalite‐rich eudialyte nepheline syenite, detached probably from the roof of the intrusion. Here, we focus on the nature of the transitional layered kakortokite and conclude, in contrast to the conventional model, that it was formed by metasomatic transformation and assimilation of naujaite autoliths. We propose that the breakdown and replacement of sodalite locally increased chlorine and sodium concentrations, which may have catalyzed the precipitation of eudialyte. In detail, we suggest that the uppermost four eudialyte‐rich horizons were strongly influenced by metasomatic processes caused by mineral‐melt reaction, and were not simply the result of conventional igneous magmatic cumulate formation, as has been inferred for the underlying kakortokite layered units. Recognition of a significant metasomatic process has important bearing on the distribution of minerals with specific elements, like REE in eudialyte, both from a petrological and an economic perspective.

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Section: The Kakortokite Sequence Northwest Of Lakseelvmentioning

confidence: 99%

Assimilation and extensive metasomatism of agpaitic rocks from the transitional layered kakortokite, Ilímaussaq Intrusion, South Greenland

Schønwandt,

Barnes,

Ulrich

2023

Resource Geology

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“…The accumulation of volatiles and residual elements under the naujaite in the roof of the lujavritic magma chamber was the cause of reactions between naujaite and the lujavritic magma resulting in alteration of the naujaite (Steenfelt & Bohse 1975) and in the formation of various reaction products (Sørensen 1962;Demin 1972).…”

Section: Information From Other Gardar Complexesmentioning

confidence: 99%

The Ilímaussaq alkaline complex, South Greenland – an overview of 200 years of research and an outlook

Sørensen

2006

Meddr Grønland. Geosci.

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The Ilímaussaq alkaline complex, South Greenland, the type locality of agpaitic nepheline syenites and of thirty minerals, among which arfvedsonite, eudialyte and sodalite, has been studied since 1806. The paper reviews the outcome of 200 years of geological investigations and presents an overview and a synthesis of the petrology of the complex. The site of the complex was invaded successively by augite syenitic, alkali granitic and nepheline syenitic melts. Remnants of the augite syenite and granite intrusions are found along the contacts of the nepheline syenites and as xenoliths in these. The nepheline syenites, which occupy the major part of the complex, are divided into a roof series, an intermediate series and a floor series. The roof series crystallized from the roof downward in the order pulaskite, foyaite, and the agpaitic rocks sodalite foyaite and naujaite. The floor series consists of cumulates: an inferred hidden part formed simultaneously with the roof series and an exposed part of layered agpaitic nepheline syenites (kakortokites) which were formed at least partly later than the roof series. The floor series passes gradually into the overlying intermediate series consisting of the agpaitic rock type called lujavrites. The lujavrites enclose rafts of naujaite and appear to have been emplaced by piecemeal stoping. The larger lujavrite masses are floor cumulates, but lujavrite dykes and sheets occupy fractures in the roof series rocks. According to one model for the evolution of the complex, the nepheline syenites formed by consolidation of one magma batch in a closed system. The lujavrites were formed from the residual melts left after the formation of the roof series and the floor series and were sandwiched between these. A second model implies that the kakortokites and lujavrites formed from one or more separate magma pulses which intruded the already consolidated roof series rocks. This model is supported by new information on contact relations and especially on the petrology and geochemistry of a marginal pegmatitic facies that forms a rim around the kakortokite-lower aegirine lujavrite part of the complex. It consists of a massive-textured matrix intersected by pegmatites. The matrix was the first rock to form in the lowermost exposed part of the complex and gives information about the composition of the initial magma of the kakortokite-lujavrite sequence. It is concluded that the agpaitic rocks of the complex were formed from at least two successive magma injections, which formed respectively the roof series and the kakortokite-lujavrite sequence.

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Interpretation of field observations in the southern part of the Ilímaussaq intrusion, South Greenland

Cited by 2 publications

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Assimilation and extensive metasomatism of agpaitic rocks from the transitional layered kakortokite, Ilímaussaq Intrusion, South Greenland

Assimilation and extensive metasomatism of agpaitic rocks from the transitional layered kakortokite, Ilímaussaq Intrusion, South Greenland

The Ilímaussaq alkaline complex, South Greenland – an overview of 200 years of research and an outlook

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