Metagabbros and metabasalts were recovered during Leg 149. Metagabbros from Site 900 (Figs. F1, F2) consist of plagioclase, clinopyroxene, and amphibole and were metamorphosed under amphibolite to granulite grade conditions (Cornen et al., 1996). Metabasalts were recovered as basaltic and diabasic clasts at Site 899, ~60 km to the west of Site 900. The Site 900 metagabbros and Site 899 metabasalts provide evidence for variability in parental melt compositions with trace and rare earth element concentrations that would be comparable to transitional- to enriched-type mid-ocean ridge basalt. Because of this range in compositions, the mantle source region may have been heterogeneous (Cornen et al., 1996; Seifert et al., 1996; Seifert and Brunotte, 1996). However, other factors, such as the nature of the mantle source region (oceanic vs. continental), depth of partial melting within the mantle, and variable extents of partial melting may have also affected the parental melt compositions of the Leg 149 protoliths.
Sites 1067 and 1068 from Leg 173 were located on the same structural high as Site 900 from Leg 149 (Figs. F1, F2). Results from whole-rock shipboard analyses showed that Leg 173 (Sites 1067 and 1068) amphibolites and metagabbros have tholeiitic affinities and were compositionally distinct with lower Mg numbers and higher trace element contents compared to the Leg 149 metagabbros (Whitmarsh, Beslier, Wallace, et al., 1998). The age of the Site 1067 amphibolites has been determined to be ~270 Ma, based on dating of magmatic zircons, and most likely represents the intrusion age during the Hercynian (Manatschal et al., in press). These amphibolites, therefore, predate the opening of the Atlantic ocean basin in this region at ~126 Ma (Whitmarsh and Miles, 1995) and predate the upwelling and partial melting of the mantle to produce basaltic liquids associated with rifting.