The nature and composition of rock samples dredged from the Mid-Atlantic Ridge between 22°N and 52°N

Abstract

Dredge hauls along the Mid-Atlantic Ridge between 22°N and 52°N have brought up various rock types including basalts, serpentinites, gabbros and dolerites. The basalts are of particular interest in that numerous fragments have been obtained with well developed glassy margins. Although the interiors of these fragments are often cryptocrystalline and not readily determinable by optical examination, chemical analysis has demonstrated that the basalts are of tholeiitic character. Amongst them high alumina olivine tholeiite is represented, comparable to the basalt of the Medicine Lake Highlands in California. Glass of this composition clearly demonstrates that magma of high alumina characteristics can exist in a wholly liquid condition. The presence of such glass on freshly fractured fragments dredged from the ocean floor demonstrates that such high alumina basaltic magma cannot be restricted to the continental areas of the earth. Distinct differences exist between the compositions of the dredged basalts and those of basalts exposed on the islands along the Mid-Atlantic Ridge, but there are similarities between the basalts dredged from the Mid-Atlantic Ridge and those obtained by Wiseman (1937) from the Carlsberg Ridge in the Indian Ocean.