Abstract

J. E. M. White said that with reference to the eastern contact zone, a photograph was presented showing inclusions of hornfelsed gabbro that are apparently undisplaced, in a structural sense, in the ultramafic host; indeed, they literally seem to be suspended within the latter. Could this anomaly be conceivably resolved through recourse to a model involving either selective assimilation or fluidization?

Regarding the fine grained late ultramafic dykes cutting both the intrusion and the eastern contact aureole, you observed that an amphibole is present and as these veins are widespread, despite their generally aphanitic texture, could it be possible that a rather high water content would have greatly enhanced the fluidity of this particular magma? Moreover, there may be some interrelation between the formation of the hornblendite facies in the comparable ultrabasic plutons of SE Alaska and the development of the amphibole in the late dykes of the Reinfjord complex.

Finally, within this context of the dyke magmas, can you account for the increasing basicity of the main intrusion as a whole, a trend which ultimately culminated in the emplacement of the central core of dunite? Could a progressive melting of the upper mantle be involved here as has been envisaged for the se Alaskan analogues?

Dr B. E. Leake supported the author’s interpretation. The sequence of intrusions, commencing with gabbro and culminating in a dunite core was extremely difficult to explain by crystallization from one magma unless the ultramafic rocks were emplaced in their present position as already crystallized

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