Abstract
1972 has seen a further development of the trend noted in Report of Activities, 1971 towards detailed isotopic studies of particular petrological and geochronological problems rather than the regional programmes of K/Ar mineral age determinations carried out previously. As the main picture of Greenland geochronology emerges so the problems to be solved become more complex and require close cooperation and mutual understanding between field and the laboratory investigators. In many studies the limits of the currently available field and laboratory techniques have been reached and in several cases now under investigation interpretation of the results involves a much more exact knowledge of the conditions under which the various rock and mineral systems become closed to loss of radiogenic daughter elements.
Highlights
(3) Basement rocks in the Nagssugtoqidian and Rinkian mobile belts The area of Precambrian gneisses north of Søndre Strømfjord which gives a regional K/Ar age of approximately 1700 m.y
Chessex reports that the zircons from the highly deformed rocks show no evidence of a major thermal or tectonic event around 1700 m.y., the K/Ar age obtained for rocks in the Nagssugtoqidian mobile belt
First results of this work are given in Pidgeon (1973) and report a U/ Pb concordia age of 3030 m.y. for a zircon separated from a granite formed at a relatively late stage in the geological development of the area
Summary
(3) Basement rocks in the Nagssugtoqidian and Rinkian mobile belts The area of Precambrian gneisses north of Søndre Strømfjord which gives a regional K/Ar age of approximately 1700 m.y. Chessex reports that the zircons from the highly deformed rocks show no evidence of a major thermal or tectonic event around 1700 m.y., the K/Ar age obtained for rocks in the Nagssugtoqidian mobile belt.
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