No abstract

During Leg 38 basalt, dolerite, and gabbro-dolerite were recovered from nine sites in the Norwegian-Greenland Sea. The upper part of the acoustic basement of two sites (Site 345 on the eastern flank of the Mohns Ridge, and Site 350 on the southern part of the Jan-Mayen Ridge) consists of highly altered basaltic (tuff) breccia. In the upper part of basement at Site 336 (the northern slope of the Iceland-Faeroe Ridge), there is a red chemical weathering crust which grades downward into fresh basalt. Relics of basaltic eluvium were also found in the upper part of basement at Site 342 (the V0r-ing Plateau). Flow basalt was recovered at only two sites (Site 337 on the eastern flank of the Norwegian Seamounts and Site 345 on the eastern flank of the Mohns Ridge). Hole 344 (on the Knipovich Ridge) recovered a subabyssal intrusive body of dolerite (diabase), gabbro-dolerite, and gabbro. Basalt of other sites (336, 338, 342, 343, 348, 350) may be the sills or dikes; however, the presence of thick basalt flows is not improbable. The basalts have different degrees of alteration; the basalt at Site 343 has the most alteration and the basalt at Site 350 has the least alteration.Based on chemical characteristics the basaltic rocks are divided into two main types: (1) low-alkaline tholeiite (Sites 336, 338, 348), and (2) alkaline and subalkaline basalt (Sites 337, 342, 343, 350). High-alumina subalkaline basalts are present at Site 350. Except for Sites 344 and 345, basalts of all others site have a high iron content. This is typical for the northern Atlantic volcanic province. A high titanium content is also notable. It should be noted that the Leg 38 basalts are: (1) closely related to the Paleogene-Neogene plateaubasalt of East Iceland and Faeroe Islands (Sites 337 342, 350); (2) are similar to the tholeiites of the Mid-Atlantic Ridge (Sites 336, 338, 348), differing from them by low magnesium content and a high iron content; and (3) they are similar to transform fracture zone basalts (Sites 343, 344, 345). However, the basalts of any region have their own specific properties. This suggests heterogeneity of the earth's crustal structure and in the composition of the mantle.