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The Trachybasaltic Suite of Jan Mayen |
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| Authors: | MAALOE SVEN; SORENSEN IB; HERTOGEN JAN |
| Institution: | 1Institut for Geologi Allegaten 41, 5014 Bergen, Norway 2The Geological Survey of Greenland Østervoldgade 10, 1350 Copenhagen, Denmark 3Afdeling Fysico-chemische Geologie Celestijnenlaan 200C, Heverlee, 3030 Belgium |
| Abstract: | The alkalic suite of Jan Mayen is of the trachybasaltic typewith a K2O/Na2O ratio of about 1·64. The suite includesall intermediate types of lavas between ankaramite and trachyte,with ankaramites being particularly prevalent. The major andtrace element trends are well defined. A new method allows distinctionbetween fractionated and accumulative ankaramites, and it isshown that the most primitive ankaramite contains 13–14per cent MgO. Experimentally determined P-T phase relationsof this composition suggest that it might be a primary composition,formed by partial melting of a spinel lherzolitic source at19·5kb and 1415°C. The fractionation from ankaramiteto trachybasalt occurred at low pressure, and was controlledby delayed gravitative settling of phenocrysts, while the fractionationfrom trachybasalt to trachyte is explained by crystallizationon the walls of the magma chambers. |
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