Basalts from the Deep Ocean Floor

G. D. Nicholls
Geology Department, University of Manchester

Summary: Basalts dredged from the floor of the deep ocean show general tholeiitic affinities. Some samples are rich in aluminium and of very similar composition to the Warner high-alumina basalt from California. Both olivine tholeiite and high-alumina basalt have been found in the form of glass in dredgings from the Mid-Atlantic Ridge, indicating that liquid magmas of both compositions have been erupted on to the sea bed in this area. In explanation of this association a tentative hypothesis of fractional melting of hydrated upper mantle material is proposed. It is suggested that under the mid-ocean ridges the ‘basaltic fraction’ of the mantle is locally in the form of an amphibole. Fractional incongruent melting of this amphi-bole appears to be a possible explanation of the range of composition encountered in dredged glass samples.

Mineralogical Magazine; 1965 v. 34; no. 268; p. 373-388; DOI: 10.1180/minmag.1965.034.268.32
© 1965, The Mineralogical Society
Mineralogical Society (