40 Ar- 39 Ar ages of lavas from the southeast Greenland Margin, ODP Leg 152, and the Rockall Plateau, DSDP Leg 81

Abstract

Ar- 39 Ar incremental heating experiments were performed on volcanic rocks recovered by drilling during Ocean Drilling Program Leg 152, southeast Greenland Margin (63°N), and Deep Sea Drilling Project Leg 81, southwest Rockall Plateau (56°N). Both of these legs drilled into thick sections of submerged lava flows, known as seaward-dipping reflector sequences, that are part of the Tertiary North Atlantic Volcanic Province (NAVP). Results show that subaerial volcanism began at the southeast Greenland Margin as early as 61-62 Ma with the eruption of continentally contaminated lavas. After an apparent hia- tus, volcanism continued with the subaerial eruption of noncontaminated, mid-ocean-ridge basalt (MORB) -like lavas. A sill or flow was emplaced at 52 Ma into the sediments overlying the basement lavas at the most seaward site (918). The MORB-like lavas of the Rockall Plateau gave poor results, although the data suggest that they erupted at 57 -58 Ma and may be contempo- raneous with the compositionally similar oceanic lavas of Leg 152. Compiled ages from the NAVP indicate that most of the lavas were erupted in two distinct magmatic episodes. The first occurred prior to 60 Ma with volcanism at the southeast Greenland Margin, in West Greenland, and the northwest British Isles. This early stage of widespread volcanism most likely records the arrival of the Iceland mantle plume. The second phase of magmatism began about 57 Ma with voluminous basaltic eruptions centralized along the eventual line of continental separa- tion. Magmatism at this stage was associated with continental breakup and asthenospheric upwelling with probable thermal input from the mantle plume.