Original paper

Magmatic CO2, brine and nitrogen inclusions in Sveconorwegian enderbitic dehydration veins and a gabbro from the Bamble sector, Southern Norway

Knudsen, Trine-Lise; Lidwin, Arne

European Journal of Mineralogy Volume 8 Number 5 (1996), p. 1041 - 1064

107 references

published: Oct 30, 1996
manuscript accepted: Jun 17, 1996
manuscript received: Jan 5, 1996

DOI: 10.1127/ejm/8/5/1041

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ArtNo. ESP147050805013, Price: 29.00 €

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Abstract

Abstract Four metamorphic stages, called M1 to M4, can be recognized in the core of the granulite fades Bamble sector of Southern Norway. M1 conditions of p = 3.1-4.1 kbar, T = 750-850°C, are connected with the emplacement of numerous gabbro intrusions (1230-1110 Ma). The following M high-grade Sveconorwegian metamorphism (1150-1070 Ma) is estimated at 5.9-9.1 kbar, 790-840°C, and involves intrusion of mm to one meter wide enderbitic veins. M3 involes isoclinal folding and restricted retrograde mineral growth in the rocks. It occurred at p-T conditions of 1.7-5.6 kbar, 510-350°C (M4). Brine inclusions with a salinity of approximately 80 wt% and pure nitrogen inclusions of relatively low molar volume (minimum 44 cm /mole), are present as early fluids in the syn-Mi gabbro-pegmatites and were probably introduced from the surrounding metapelites during gabbro crystallization. Fluid inclusion textures indicate that the brine and nitrogen were immiscible during entrapment. Enderbitic veins intruding at M2 carry CO2 as a magmatic fluid which induced a 4 -5 mm wide dehydration zone in the surrounding rocks. The width of this zone is independent of the width of the enderbitic veins. Pure nitrogen inclusions (with minimum molar volume similar to nitrogen inclusions in the gabbropegmatite) occur mainly in those enderbitic intrusions which crosscut metapelites. All rocks show similar fluid density distributions suggesting that the densities of the early fluid inclusion were reset along the steep early retrograde uplift path and that CO2 was introduced in the gabbro-pegmatite along secondary trails at this stage. Fluid evolution during the (M3) isoclinal folding of the rocks is dominated by decrepitation and retrapping of the earlier trapped fluid inclusions along secondary trails. The present data highlight differences in metamorphic fluids present in the high-grade Bamble sector during the Sveconorwegian evolution: Brine ± nitrogen and CO2 ± nitrogen are present at low to medium pressure Mi conditions and at granulite-facies M2 conditions respectively

Keywords

enderbitegabbro-pegmatitefluid inclusionsearly Sveconorwegian brinebrine-N2 immiscibility.