Autometasomatic alteration of gabbro, Kap Edvard Holm intrusive complex, East Greenland

Elsdon, R.

doi:10.1180/minmag.1982.045.337.25

Cited by 10 publications

(3 citation statements)

References 15 publications

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“…Mineral assemblages similar to those described above have been reported from other gabbros in East Greenland (Elsdon 1982;Rose & Bird 1986) and in regionally metamorphosed iron-rich gabbros in Quebec (Klein 1984). These areas of intense alteration and fracturing appear to represent localized zones of high permeability during the latest stages of cooling of the Skaergaard intrusion.…”

Section: Amphibole Veinssupporting

confidence: 80%

Mineralized fracture systems of the Skaergaard intrusion, East Greenland

Bird,

Rogers,

Manning

1986

Meddr Grønland. Geosci.

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Extensive fracture systems in the Skaergaard intrusion, including veins, sills and dikes, constitute channels for the flow of magmas and hydrothermal solutions during the subsolidus cooling and deformation of the intrusion. The abundance, orientation, transgressive relations and mineralogy of these fracture systems provides a record of fluid transport and chemical reactions during the Skaergaard's subsolidus cooling history. The earliest mineralized fractures in the Layered Series are gabbroic pegmatites that occur as veins, sills and irregular patches. These structures are crosscut by leucocratic granophyres. Veins filled with hydrothermal minerals occur throughout the Skaergaard intrusion and its host rocks. Hydrothermal minerals in veins are similar to mineral assemblages found in metabasalts ranging in grade from upper amphibolite to zeolite facies. The earliest hydrothermal veins contain upper amphibolite facies assemblages. They are <1-2 mm wide, continuous for tens of metres and occur with frequencies of 0.2 to >1.5 and 1.4 to >20 fractures/metre in the Layered Series, and Marginal Border Group and contact metamorphosed basalts, respectively. These early veins are inferred to have formed at temperatures of >500° to 750°C and <925°to 960°C. Later vein types contain mineral assemblages characteristic of lower amphibolite, greenschist and sub-greenschist facies and occur as more localized fracture systems than the early, high temperature vein types. Compositions of secondary minerals from all of these hydrothermal vein types show systematic changes relative to both the overall fractionation trend and local modal variations in the igneous mineralogy of the Skaergaard intrusion. Observed phase relations and fracture abundances are, in general, consistent with isotopic and transport characteristics of the Skaergaard magma-hydrothermal system reported by Taylor & Forester (1979) and Norton & Taylor (1979).

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Section: Amphibole Veinssupporting

confidence: 80%

Mineralized fracture systems of the Skaergaard intrusion, East Greenland

Bird,

Rogers,

Manning

1986

Meddr Grønland. Geosci.

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“…Metasomatism is widely used to describe the chemical alteration of solid rocks and minerals by external fluids, but the definition of metasomatism (e.g., Lindgren, 1933;Ramberg, 1952;Best and Christiansen, 2001;Pirajno, 2013) does not exclude the possibility that partially crystallized magmas may start being metasomatized by their own fluids: autometasomatism is a special case of metasomatism whereby the metasomatic agent is sourced from the same magmas that are being metasomatized (e.g., Elsdon, 1982). In a magmatic-hydrothermal context this necessitate that (1) the magmatic volatile phase be exsolved from the melt but stay in the magma as it crystallizes, and (2) either the rock or the fluid change its chemical composition so they lose their thermodynamic equilibrium.…”

Section: Introductionmentioning

confidence: 99%

Evolution of Montviel alkaline–carbonatite complex by coupled fractional crystallization, fluid mixing and metasomatism — part I: Petrography and geochemistry of metasomatic aegirine–augite and biotite: Implications for REE–Nb mineralization

Nadeau

Stevenson

Jébrak

2016

Ore Geology Reviews

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Magmatic volatiles are critically important in the petrogenesis of igneous rocks but their inherent transience hampers the identification of their role in magmatic and mineralization processes. We present evidence that magmatic volatiles played a critical role in the formation of the 1894 Ma Paleoproterozoic Montviel alkalinecarbonatite complex, Canada, and the related carbonatite-hosted REE-Nb deposit. Field and drill core relationships indicate that lithological units of the complex were emplaced in the following order: clinopyroxenites, melteigites, ijolites, melanosyenites, leucosyenites, granites, lamprophyric silicocarbonatites, rare magnesiocarbonatites, calciocarbonatites, ferrocarbonatites, late mixed carbonatites, kimberlitic silicocarbonatites and polygenic breccias. Magmatic minerals within these units were systematically metasomatized. In undersaturated silicate rocks, augite recrystallized to aegirine-augite and aegirine, plagioclase recrystallized to albite, and nepheline recrystallized with analcime, cancrinite and albite. Primary biotite was replaced by secondary, REE-rich metasomatic biotite, particularly along fractures and alteration pockets. In carbonatites, liquidus phases consisted of calcite and dolomite and were recrystallized to ferroan dolomite, ankerite, siderite, barytocalcite, witherite and strontianite, which are intimately related to the REE-bearing carbonates and fluorocarbonates. Biotite is common to all lithologies, ranges in REE concentrations from 1.5 to 230 ppm and yielded subsolidus crystallization temperatures ranging from 770°C to 370°C. Sm-Nd isotope analyses from biotite and aegirine-augite yield a range of ε Nd values (+3.4 to −3.0) that suggests mixing of fluids from three sources during the crystallization of the Montviel magmas. The clinopyroxenites to melteigite, ijolites and melanosyenites crystallized augite and biotite with initial ε Nd value ≥ 3.4 and these minerals were metasomatized by a 1st fluid, lowering their ε Nd to values comprised between 0.8 and 3.4. Silicocarbonatites and carbonatites subsequently crystallized aegirine-augite and biotite with initial ε Nd value ≥2.6 and a 2nd fluid metasomatized the minerals to lower ɛ values. Both the 1st and the 2nd fluids eventually mixed with a 3rd recrystallizing aegirine-augite and biotite and lower their εNd values down to −3.0. The results presented herein suggest that the mantle magmas evolved through 4 distinct mantle pulses by fractional crystallization, mixing of depleted mantle fluids with crustal fluids, and metasomatism. Some of the silicate rocks also show evidence of assimilation of wall rock as part of their petrogenetic evolution. During the last stages of its evolution in carbonatites, the fluid source transited from the depleted mantle to the crust and we speculate that this resulted in a violent explosive eruption creating the diatreme-shaped, HREE-rich polygenic breccia.

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“…2). The earlier gabbro cumulates and other basic rocks, on the other hand, have been reported fully by Deer & Abbott (1965) , Elsdon (1969Elsdon ( , 1970Elsdon ( , 1971aElsdon ( and b, 1972Elsdon ( , 1982, and Abbott & Deer (1972).…”

Section: Wmentioning

confidence: 86%

Syenitic and associated intrusions of the Kap Edvard Holm region of Kangerdlugssuaq, East Greenland

Deer,

Kempe,

Jones

1984

Meddr Grønland. Geosci.

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Kap Edvard Holm, near Kangerdlugssuaq, forms part of one of the six Tertiary igneous centres of southern East Greenland. The plutonic rocks are mainly cumulate gabbros but there are several syenite masses, together with some minor granophyres and other acid rocks. The larger syenites - Kap Boswell, Kap Deichmann, and Hutchinson Gletscher I - are intruded as conical masses into the gabbros with an intermediate ring of igneous breccia. The petrography, mineralogy, and bulk chemistry of the rocks are reported. The syenites are generally nordmarkitic, containing hedenbergite and aegirine-augite, and amphiboles ranging from hastingsite, ferroedenite, and ferrorichterite (katophorite) to arfvedsonite, while aenigmatite is quite common in the Kap Boswell and Barberkniven syenites and veins. Many rock and mineral analyses are given. An estimate of the composition of the parent magma gives a nordmarkitic liquid very close to that of the main peripheral intrusions at Kangerdlugssuaq and also to the quartz trachytic late differentiate of the Azores alkali basalt. This agrees with the authors' earlier suggestion that all the syenite masses were most probably the products of a quartz trachyte magma, fractionated in the case of the main intrusion to yield the range of rock types occurring there, and itself produced by differentiation of an alkali basalt magma such as yielded some of the many dykes present in the region. An alternative explanation, proposed by Brooks & Gill (1982), that the main intrusion derived from the reaction of a foyaitic magma, fractionated from a nephelinitic parent, with the enclosing gneisses and basalts, could not have been repeated so exactly throughout the minor peripheral intrusions at Kangerdlugssuaq and again at Kap Edvard Holm.

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Autometasomatic alteration of gabbro, Kap Edvard Holm intrusive complex, East Greenland

Cited by 10 publications

References 15 publications

Mineralized fracture systems of the Skaergaard intrusion, East Greenland

Mineralized fracture systems of the Skaergaard intrusion, East Greenland

Evolution of Montviel alkaline–carbonatite complex by coupled fractional crystallization, fluid mixing and metasomatism — part I: Petrography and geochemistry of metasomatic aegirine–augite and biotite: Implications for REE–Nb mineralization

Syenitic and associated intrusions of the Kap Edvard Holm region of Kangerdlugssuaq, East Greenland

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