Stratigraphy and correlation of the region surrounding the IRDP drill hole 1978, Reydarfjordur, eastern Iceland

Abstract

The 1.9 km thick sequence intersected by the IRDP 1978 drill hole at Reydarfjordur, eastern Iceland, is correlated with the westward dipping exposed volcanic pile on the basis of extensive field mapping and paleomagnetic studies. The base of the landward extension of sea floor magnetic anomaly 5 (epoch 9) can be located at the top of the Grjota olivine tholeiite formation, intersected at about 1.5 km in the core and exposed at sea level about 9 km east of the drill site. Other exposed marker formations can also be identified in the core. The drill site is located within a relatively dense dyke swarm (10% crustal dilation), previously interpreted as the feeder of the overlying volcanic formations. Field observations, including vertically discontinuous dykes and the lack of lava‐feeder relationships, suggest that the dykes were intruded by lateral injection from the south and are considerably younger than, and thus could not have fed, the exposed lava pile in the vicinity of the drill site. It is proposed that about 10.3 m.y. ago (roughly coinciding with the lower boundary of anomaly 5) the Reydarfjordur volcanic center ceased to be active and volcanic activity shifted about 20 km to the west, where the Breiddalur and Thingmuli volcanic centers later developed. The exposed stratigraphic succession between Thingmuli and Reydarfjordur volcanic centers is composed of lavas deposited in flank areas, relatively removed from a paleovolcanic zone, which now probably lies buried to the west of the IRDP drill site. The lowest 450 m of the core may represent lavas related to activity in the Reydarfjordur volcanic center 13.5 km to the east.