Magnetostratigrahy of the exposed lava section east of the IRDP drill hole in Reydarfjordur, eastern Iceland

Abstract

Magnetic polarity directions (VGP) of 154 exposed Miocene basalt lavas from Reydarfjordur, eastern Iceland, can be used successfully for correlation with the IRDP drill core. Three partly synchronous lava sections east of the drill site are predominantly normally magnetized and are stratigraphically of the same age as lavas dated (K‐Ar) at about 9 to 10.5 m.y. (McDougall et al., 1976). The age range and magnetic properties of these lavas, the landward equivalents to marine magnetic anomaly 5 (epoch 9), suggest that several reversely magnetized lavas in one of the investigated sections were remagnetized by a 10 m thick dyke. The data presented suggest that in fresh lavas with low Curie temperatures, relatively thick dykes (about 10 m) may cause thermal overprinting of the host rocks to a distance from the dyke equal to its thickness. These results are in contrast with the generally accepted thesis that dykes affect host rocks only up to about 1/5 of their thickness. No systematic decrease in magnetic intensity with depth was observed for a 0.9 km thick vertical lava section in Holmatindur, about 13.5 km east of the drill site. It is suggested that the heterogeneity of the lava pile in terms of magnetic intensity reflects primarily the distinct geochemistry and/or grain size of magnetic phases of individual lavas.