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| Titel: |
Geochemistry of Middle Proterozoic mafic and composite mafic-felsic dykes in southeastern Sweden |
| Auteur: |
Nilsson, Magnus |
| Verschenen in: |
GFF |
| Paginering: | Jaargang 114 (1992) nr. 1 pagina's 113-130 |
| Jaar: |
1992-03-10 |
| Inhoud: |
Mafic and composite mafic-felsic dykes of Middle Proterozoic age occur within the general area of the Transscandinavian Igneous Belt in southeastern Sweden. The composite dykes consist of felsic, quartz-feldspar porphyritic cores and mafic margins. The mafic rocks are altered with pyroxene typically replaced by amphibole and plagioclase by sericite or epidote. Two subalkaline groups can be distinguished among the mafic dykes. A tholeiitic group comprises NE-trending mafic dykes in the southern part of the area, some NW-trending dykes further north, and all the mafic margins of the composite dykes irrespective of dyke trend. The calc-alkaline dyke geochemistry is constrained mainly to NE-trending dykes in the northern part of the studied area. Within both groups there is enrichment of LIL-elements to contents above those of normal within-plate tholeiites. This was caused by metasomatism across the dyke contacts during greenschist-facies metamorphism and to some extent probably also by crustal contamination. The REE contents are those of normal continental tholeiites. Geotectonic discrimination diagrams indicate oceanic or arc affinity which is in conflict with the ensialic setting of the dykes. This is in accordance with studies of continental tholeiites elsewhere. Field relationships suggest that the composite dykes were formed by semi-synchronous intrusion of mafic and felsic magma. However, trace elements and the REE distribution indicate that the two magmas were not derived from a single parental melt. A possible explanation is that the mafic magmatism caused anatectic melting in the lower crust. The two magmas then intruded more or less simultaneously. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
Details van artikel 5 van 23 gevonden artikelen
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