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- Volume 92 (1969)
- Fascicule 2
- La variation du rapport (87Sr/86Sr)0 dans les roches génétiquement associées au magma plagioclasique
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La variation du rapport (87Sr/86Sr)0 dans les roches génétiquement associées au magma plagioclasique
Abstract
Determinations of (87Sr/86Sr)0 in representative rocks of different units of the igneous, mainly anorthositic, complex of South Rogaland and its gneissic cover yield the following indications.
1. The anorthositic core of the Egersund-Ogna massif (considered as magmatic) is characterized by a low initial ratio (0.704-0.705) indicative of a mantle derivation without or with very little crustal contamination. The leuconoritic gneissic border of the same massif has however higher ratios.
2. The first (anorthosito-noritic) and second (monzonoritic) phases of the Bjerkrem-Sogndal lopolith are characterized by a higher ratio (0.707) in accordance with the assumed origin, by crustal contamination, of the plagioclasic magma.
3. Still higher ratios (0.711-0.713) are observed in the third (mangeritic) phase of the same massif, apparently pointing to a still higher contamination at this stage. The values observed may even be little different from that of the average wall gneiss. The data relative to these last rocks are still too scarce to allow the verification of that point.
4. The anatectic leuconorite, and paraanatectic anorthosite of the Haaland-Helleren massif, formed at the expense of the border of Egersund-Ogna and the first phase of Bjerkrem-Sogndal, have initial ratios in accordance to their accepted origin.