C.G. Engel B.P. Luyendyk 1969 <div id="Abs1-section" class="c-article-section"><div id="Abs1-content" class="c-article-section__content"><p>OVER the years, samples of basalt from the oceanic crust have been taken mainly from seamounts, fracture zones and ridge and rise crests^1–6, and rarely from the vast fields of abyssal hills which cover a large part of the deep-sea floor. The basalt sampled from the deeper regions of the oceanic crust (for example, on fault scarps) is a distinct variety of tholeiitic basalt, while alkali basalt is restricted to the volcanic edifices⁴. Oceanic tholeiitic basalt differs from alkali basalt and continental tholeiite chiefly in having a relatively low percentage of K₂O (0.2 weight per cent)⁴. Some authors have speculated that this type of tholeiitic basalt is the major extrusion from the upper mantle and constitutes the predominant rock type in the upper oceanic crust.</p></div></div> application/pdf 10.1038/2231049a0 en Nature Petrological, magnetic and chemical properties of basalt dredged from an abyssal hill in the North-east pacific article