An Unusual Enstatite-Forsterite Basalt from Kolbeinsey Island, North of Iceland
This is the first account of volcanic rocks erupted from a northern extension of the MidAtlantic Ridge to a locality between Iceland and Jan Mayen. The islet of Kolbeinsey (67° 08' N., 18° 36' W.) is being rapidly eroded and now measures 52×36 m, and reaches only to 7.5m above sea level. T...
| Published in: | Journal of Petrology |
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| Main Authors: | , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
1970
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| Subjects: | |
| Online Access: | http://petrology.oxfordjournals.org/cgi/content/short/11/2/205 https://doi.org/10.1093/petrology/11.2.205 |
| Summary: | This is the first account of volcanic rocks erupted from a northern extension of the MidAtlantic Ridge to a locality between Iceland and Jan Mayen. The islet of Kolbeinsey (67° 08' N., 18° 36' W.) is being rapidly eroded and now measures 52×36 m, and reaches only to 7.5m above sea level. Two identical specimens of vesicular basalt were collected by the Icelandic Coastguard vessel Aegir in 1962, and have now been chemically analysed. The mineral compositions were determined by electron microprobe analysis. The rock carries micro-phenocrysts of highly magnesian olivine (Fo 98 8 ) and of plagioclase (An 85 to An 30 ). Brown and lemon-yellow grains of augite (Wo 42 En 45 Fs 13 ) are accompanied by pale-yellow, euhedral to subhedral, groundmass orthopyroxenes of highly magnesian composition (Wo 4 En 88 Fs 8 ) and with a calcium content higher than found previously in enstatites. The chemistry of the basalt, also, is unusual in showing Fe 2 O 3 = 8.98 per cent and FeO = 0.38 per cent. The high state of oxidation is considered in relation to the production of forsterite and enstatite from basalt magma. Historic submarine volcanism in the region is discussed in relation to bathymetric and geophysical data. |
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