DISCUSSION OF PAPERS PUBLISHED IN PREVIOUS PARTS OF THE QUARTERLY JOURNAL

Abstract

From Dr B. J. W alton : A similar association is present north of Narssarssuaq, South Greenland (Walton, in the press). In this area there are two large intrusive complexes comprising noritic gabbros, hypersthene-augite- and hornblende-bearing diorites, and hypersthene-monzonite. These are clearly younger than the main phases of regional metamorphism, folding, and granitization but slightly older than an extensive phase of granitic development. The younger granite forms very large bodies and invades the basic rocks. The basic-intermediate rocks constitute an appinitic suite with close similarities to the Caledonian intrusive complexes of Scotland. With reference to the Caledonian fold-belt and to the orogeny which developed in Ketilidian (Pre-Cambrian) times in South Greenland, these bodies are best described as late-orogenic, using the term orogeny to refer to the complete sequence of events in the development of the fold-belt. Tyrrell (1955) showed that these rocks occupy a characteristic position in the tectono-igneous cycle. There is evidence that in South Greenland the basic rocks were intruded almost contemporaneously with the younger granites rather than during the geosynclinal phase, as suggested by Hutchison for the Singapore association. It seems likely that these rocks are characteristic of the epeirogenic uplift phase of an orogeny. Tensional conditions could prevail in part during this phase, which would allow introduction of simatic basaltic material. Extensive contamination by sialic material may cause the development of the appinitic suite. The younger granites are probably mainly palingenetic in origin.