A gravity survey across the Gardar Igneous Province, SW Greenland

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Abstract
The Gardar Igneous Province is believed to involve the remains of Proterozoic rifting which evolved through repeated phases of activity around 1300 Ma, 1250 Ma and 1170 Ma ago. A gravity survey across part of the province has established the presence of a gravity 'high' of some 300 g u amplitude which is 30 km wide and elongated ENE–WSW, centred on Tunugdliarfik and axially along one of the main zones of Gardar intrusives. This gravity anomaly is similar to that of other ancient rift systems and appears to be a residual of the axial anomaly to be found in modern active rifts. It is interpreted in terms of a basic mass underlying a late Gardar rift, some 50 km long and 25 km wide, intruding the crust. Evidence suggests the Gardar rifting cannot be explained in terms of a major crustal separation as an extension of the mid-continental rift and Keweenawan systems of North America. It is more consistent with crustal stretching of no more than 10 km and possibly diapiric mechanisms. The coastal gravity gradient appears to be due to a change in crustal thickness coincident with the coastline, some 25 km beyond the present ice cap limit. Although Greenland may be in overall isostatic balance, it seems that the coastal zone remains overcompensated.