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General geological results of the Leg 49 drilling program are discussed without emphasis on petrologic and geochemical data. Three holes (407, 408, and 409; Figure 1) were drilled on the west flank of Reykjanes Ridge. Our results suggest that the ridge has been anomalously shallow, relative to the worldwide average ridge depth, since at least 36 m.y. ago (anomaly 13). It is clear, however, that thermal or tectonic events during the past 17 million years have perturbed the ridge depth profile, and perhaps bias the simple backtracking results for older crust toward anomalously shallow depths. On the basis of our results, regional uplift, with an average vertical component of up to 25 meters per million years since 36 m.y. ago, is possible and cannot be excluded. Other holes are close to the crest of the Mid-Atlantic Ridge (410 and 410A) or in the rift valley itself (411). None of the ridge-crest sites (including 409) shows evidence of hydrothermal alteration and all rocks are extremely fresh. Magnetic properties show evidence of oxidation of Hole 410A basalts, however. Generally, all sites show a degree of alteration which correlates strongly with age, suggesting long-term reaction between basalts and cold sea water. Two sites, 412 and 413, are in fracture zone B in the FAMOUS area. The rocks here are generally fresh and unaltered basalts similar to rocks recovered from the rift mountains by dredging and during Leg 37. Even though Site 412 is in the north side of the valley and 413 is in the south, they are both the same age, and match the age of the magnetic anomaly on the young (north) side of the valley.

General Implications of the Leg 49 Drilling Program for North Atlantic Ocean Geology