Dynamic support by the Icelandic plume and vertical tectonics of the northeast Atlantic continental margins

Late Paleocene-early Eocene continental rifting in the northeast Atlantic differs significantly from earlier episodes of margin formation in the Central Atlantic. At a nonvolcanic margin, rifting occurs over a wide area, with little associated magmatism. Postrift subsidence decreases in a predictable, exponential pattern with time. In contrast, subsidence analysis of Ocean Drilling Program and Deep Sea Drilling Project drill sites from the Voring Plateau, Hatton Bank, and East Greenland Margin show that in these areas the continent-ocean transition (GOT) is very sharp, with beta increasing over a horizontal distance of 30-50 km from values of 1.1-1.50 on the continent side to infinity at the GOT. Drilling penetrated the thick seaward dipping basaltic sequences that typify the East Greenland Margin at Site 917. Fluvial sandstones underlying the basalts show that the area was subaerially exposed prior to continental breakup, but the amount and timing of any uplift are presently unconstrained. Sediment backstripping techniques allow a comparison between the reconstructed and predicted subsidence histories and thus an estimate of the thermal anomaly through time. Anomalous slow subsidence in the early postrift period at 63 degrees N offshore East Greenland is attributed to support by the Icelandic plume. Dynamic support is weaker on the Hatton Bank and on the Voring Plateau. Variations in the strength and duration of the support suggest that the plume was a large, 1000-km-radius structure that lay under the Greenland craton at the time of breakup. Current data suggest that it may have crossed the East Greenland coast at 40 Ma. Discrepancies between uniform stretching models and the reconstructed subsidence for sites on the East Greenland shelf and the Voring Plateau allow the amount of igneous underplating at the time of breakup to be estimated. Calculations suggest a maximum of around 8.8 km of gabbroic underplating occurred at the time of breakup under the East Greenland shelf and 2.4 km under the Voring Plateau, although both these bodies thin rapidly away from the GOT.