163 Preliminary Report


Despite the significant loss of operational time because of environmental conditions, extraordinary recovery of core at three critical sites provided the material to address most of the high-priority objectives of the leg. However, the main tectonic objective of drilling through the breakup unconformity and sampling the prerift crust (presumably sediments) was not fulfilled.

The following are the initial, major results of the cruise:

1. There now exists a virtually complete record of the volcanic evolution of the East Greenland margin at latitude 63°N, from earliest, depleted and continentally contaminated, relatively deeply segregated magmas, through breakup-related picritic and tholeiitic magmas derived by shallower and larger degrees of melting, to a steady-state oceanic magma series.

2. Preliminary identification of two magnetic polarity reversals, the first ever recorded from the early Tertiary age volcanic materials of East Greenland, and the recovery of fresh, feldspar-phyric flow units suitable for radiometric dating offer the promise of a detailed and precise time scale for the volcanic activity. This basic chronology will reveal the timing and rates of volcanic and tectonic processes.

3. The Iceland plume mantle component is more strongly expressed in the compositions of basalts at latitude 66°N compared with 63°N. Together with evidence from DSDP Leg 81 (Hatton Bank, Rockall Plateau) and ODP Leg 104 (Vøring Plateau), we now have sufficient information to map the basic compositional structure of the mantle melting regime that existed during the initiation of the Iceland plume and breakup of the North Atlantic.

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