Isotopic studies in the East Greenland Caledonides (72°–74°N) – Precambrian and Caledonian ages

Abstract

Rb-Sr isotopic studies on crystalline rocks from different rock units of the East Greenland Caledonides have given a number of isochron and 'errorchron' ages, as well as sets of inconclusive data. All the results are presented here as an illustration of the problems encountered, though previously published data is given in summary form. Eleven collections from Archaean - early Proterozoic rock units have given seven early Proterozoic Rb-Sr whole rock isochrons, while one set of data points plot about a 2450 m.y. reference line. Seven collections from metasediments of presumed middle to late Proterozoic age produced only one 'errorchron' of c. 1245 m.y., but data points from all the collections plot about a 1250 m.y. reference line. Six collections from a suite of 'older' granites gave four isochron ages of 1080, 1000,765 and 650 m.y. Eight collections from Caledonian granites gave four isochron ages, three 'errorchrons' and one mineral-whole rock isochron; the ages fall in the range 377-550 m.y.