The principal objective of drilling Transect EG65 was to sample volcanic basement formed during breakup and onset of seafloor spreading in a position midway between the plume track of Transect EG68 (Greenland-Iceland Rise) and the distal drilling sites of Transect EG63 (Ocean Drilling Program [ODP] Legs 152 and 163) (Fig. F6). The SIGMA survey shows that the maximum thickness of the volcanic crust changes northward between 64° and 66°N from 18–20 to 30–32 km. Importantly, by 66°N (SIGMA-II line), the maximum crustal thickness (~28 km) is close to the thickness imaged along the entire Greenland-Iceland Rise (SIGMA-I line) (Hollbrook et al., 2001). Likewise, the composition of basalts recovered by drilling along Transects EG66 (see the "Transect EG66 Results" chapter), EG68 (see the "Transect EG68 Results" chapter), and at Site ODP 988 have close affinities to those of Paleogene Iceland and the East Greenland flood basalt province, suggesting melt generation and differentiation under similar conditions. Given the coherence of these relationships, we viewed the area of transitional crust between 64° and 66°N as the highest priority for drilling because work here could provide the critical samples to directly relate changes in crustal structure to processes of mantle melt generation and crustal accretion.
The goal of Transect EG65 drilling was to sample above and below the break-up unconformity and to recover material from the youngest portions of the seaward-dipping reflector sequences feasible with our drilling system (i.e., without sediment cover). Based on the excellent coverage by the H/S Dana survey, a transect at 65°N was selected that closely followed seismic Line DLC9709 (Fig. F1). This seismic line (Fig. F2) shows key structural elements in the uppermost crust with an inner continental basement high and an outer igneous plateau with strong seaward-dipping reflectors separated by a prebreak-up sedimentary basin. This setting is conducive to an offset drilling strategy by providing stratigraphic coverage despite limitations in drilling depth.
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