1921. No. 8. ox THE ECLOGITKS OF ^•OK\VA^• 



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with the eclogitts, but it seems to me more probable that it then crvstallized 

 primarily in the amphibolite faciès, as we assume that partly was the case 

 with the Romsdalshorn rock. 



The first stage ot" alt er at i o 11 of the enstatite, in the specimens 

 rom Su lo near A ale sund, S aet re on II are id, and Kjede and 

 Lis to in Selje appears in the development of narrow border zones almost 

 black from pigmentary material. Laura Hezner' describes quite a similar 

 phenomenon in the eclogite-amphibolite from Sulztal and believes it to con- 

 tain green hornblende. P'rom its greenish tint the alteration product in our 

 rocks would also seem to be hornblende. 



The amphibolitization being an interaction of garnet and pyroxene, 

 either of these, as a rule, will be exhausted first. Usually some garnet has 

 remained. Now, the garnets rich in pyrope are not stable in the amphibolite 

 facies, and the garnets actually presei-\ed in garnet-amphibolites have in all 

 cases so far studied proved to be rich in almandite, as shown later on. 



It might therefore be supposed that the garnets, at the amphibolitization, 

 should be enriched in almandite, but we ha\-e not yet anv positive evidence 

 on this point. 



The amphibolitization of eclogites is a diaphtoretic metamorphism in 

 the sense of Becke, or, in the language of the facies theorv, a change from 

 the eclogite to the amphibolite facies. The alteration apparently took place 

 during that time when the inclusions of eclogite were submerged in the gneiss 

 magma and the crystallization began there. The temperature had then sunk 

 to the held of stability of the amphibolite, and the presence of mineralizers 

 emanating from the magma favoured the re-crN'Stallization in the outer zones 

 C)t the inclusions and on the walls of Joints in which solutions of silicic 

 acid intruded, giving rise to quartz-veins. 



It was not determined b}' means of anal3^ses, whether any change in the 

 bulk composition w^as induced by this alteration or not, but comparing the 

 resulting amphibolites with others whose composition is known, no change 

 would seem probable, as a rule.^ But in some cases a considerable addition 

 of material is apparent. In the altered zones around the quartz veins on 

 Silden (p. 37 1 the amphibolite contains ver^- much biotite. In many othei" 

 cases the amount of plagioclase is larger than what could originate from 

 the eclogite minerals. And true resorption and assimilation also has taken 

 place, often perhaps not much, but in other cases on a large scale. 



Sometimes zoisite, epidote, margarite, and chlorite appear in the eclogites, 

 indicating that alteration has surpassed the amphibolite facies and approached 



' Loc. cit. (T. M. P. M. 22, 1903, p. 5101. 



- When this paper was already sent to the print, I received the work of M"^' Y. Brière, 

 "Les eclogites françaises — leur composition minéralogique et chimique; leur origine", 

 thesis, Paris 1920. Among many other interesting results this careful study contains 

 analytical evidence, in the case of an eclogite and its amphibolitic alteration product from 

 Puy Fcrrières, that no change of the bulk composition has taken place (op. cit. p. 55 1. 



