Title: Halogen geochemistry of fluid during amphibolite-granulite metamorphism as indicated by apatite and hydrous silicates in basic rocks from the Bamble Sector, South Norway
Abstract: The halogen chemistry of apatites, biotites, amphiboles and titanites from metabasites in the Proterozoic Bamble Sector amphibolite-granulite facies transition zone (Norway) has been studied to gather data on the behaviour of halogens during original magmatism and subsequent metamorphism. Three groups of apatites could be recognized: (1) FOH-apatites with more than 50 mole % F and virtually no Cl. (2) FOH-apatites with up to 15 mole % of Cl. (3) Cl-rich apatites with up to 6.73 wt.% Cl. The latter are the most Cl-rich metamorphic apatites ever reported. The F-contents of coexisting biotite do not follow this division, but their Cl-contents do. Log(z.sfnc;HFz.sfnc;H2O) values for the coexisting fluid phase calculated from biotite are slightly lower than those calculated from apatite. Log(z.sfnc;HClz.sfnc;H2O) values in the coexisting fluid phase calculated from biotite are substantially higher than those calculated from apatite. The log(z.sfnc;HFz.sfnc;H2O) reflects the composition of the peak metamorphic fluid phase. The apatites show three types of patterns of F-contents: (1) W-shaped, (2) Rimward increasing and (3) Rimward decreasing. Pattern (2) reflects progressive metamorphism. Pattern (3) is thought to reflect growth starting near peak metamorphism and going on during retrograde dilution of the peak metamorphic fluid by a newly introduced aqueous one. Some apatites show local resorption effects along cracks. No regional trend in calculated log(z.sfnc;HFz.sfnc;H2O) values is present. As different from other granulite terrains, the Bamble biotites and amphiboles from granulite facies samples do not have higher halogen contents as those from the amphibolite facies area. The samples show that halogen bearing fluids were controlled at a very restricted scale during peak as well as retrograde metamorphism.
Publication Year: 1993
Publication Date: 1993-06-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 43
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