Early Archaean Age for the Isua Iron Formation, West Greenland

摘要: SOME 150 km north-east of Godthaab, on the edge inland ice cap, a refolded syncline mainly basic rocks containing banded ironstones and other supracrustal origin is enclosed by granitic gneisses (Fig. 1). These have yielded an Rb-Sr whole-rock isochron age 3,700 ± 140 m.y., indistinguishable from that Amitsoq Godthaab area1. The present metamorphic grade both iron formation upper greenschist to amphibolite facies. There no published map area, but following geological details are taken reports Keto2. total succession 2 3 thick. lower part consists quartzites meta-greywackes. overlain garnet–chlorite schists formation, including Fe-oxides carbonates. top facies metabasites, Bridgwater et al.3 suggest Isua supracrustals may represent shallow-water shelf