Age and origin of agpaitic magmatism at Ilímaussaq,south Greenland: RbSr study |
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| Authors: | Alan B Blaxland Otto Van Breemen A Steenfelt |
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| Institution: | 1. Isotope Geology Division, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 OQU, Scotland;2. Grønlands Geologiske Undersøgelse, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark |
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| Abstract: | A RbSr whole-rock isochron gives an age of 1168±21 m.y. for the agpaitic units of Ilímaussaq, showing that this complex belongs to the main phase of Gardar igneous activity in south Greenland and is not, as previously supposed, a significantly younger intrusion. Moreover, the agpaites must have intruded very soon after the earlier augite syenite phase of Ilímaussaq. The initial 87Sr/86Sr ratio of 0.7096±0.0022 for the agpaites is in marked contrast to the low (～0.703) ratio obtained for the augite syenites and suggests that selective enrichment of 87Sr occurred by preferential leaching of radiogenic strontium from unstable positions in Rb lattice sites in older crustal material by the highly reactive agpaitic magma. |
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