Tectonism and magmatism during NE Atlantic continental break-up: the Vøring Margin

Abstract

The temporal and spatial relationships of tectonic and magmatic features on the Vøring volcanic margin show that continental break-up occurred in association with significant magmatic activity about 18 Ma after initiation of lithospheric extension. From the distribution of extension across the margin and the volumes of melt produced, a thermal anomaly of 50–80°C is estimated, in agreement with predictions from recent plume models. A tectono-magmatic model is proposed in which the ascending proto-Iceland plume released the rifting, over a > 300 km wide zone, by uplift-induced extension of the NE Atlantic lithosphere already affected by tensional stresses. Initial rifting took place without decompressional melting when the plume, carrying the thermal anomaly, was still 600–700 km beneath the lithosphere. Subsequently, widespread magmatism occurred when the plume impinged on, spread out beneath and infilled the rift-defined relief at the base of the lithosphere. Break-up is suggested to be a consequence of melt-induced weakening of the lithosphere, whereas the anomalously thick igneous crust at the continent-ocean transition along the NE Atlantic margins is explained by melt focusing towards the uplifted break-up axis.