The Isua block of West Greenland is composed of a belt of supracrustal rocks and surrounding granitic gneisses, both of which yield dates of approximately 3750 m.y. This age is equivalent to that of the Amitsoq gneisses of the nearby Godthaabsfjord area. From the lilhological variation and structural style, two major deformalional events are recognised in both the supracrustals and the gneisses: D1, a phase of fabric formation caused by a vertical simple shear mainly affecting rocks of the supracrustal belt; and D2. a phase of major and minor folding of the earlier structures probably caused by an ENE–WSW ductile dextral simple shear movement. Measurements of the amount of strain from a distinctive conglomeratic unit yield strain paths for the two deformations and a value of vertical displacement of approximately 7 km for D1. Two dyke sets invade the supracrustals and gneisses, a tangential set during D2 and a radial set after D2.

You do not currently have access to this article.