Ip. Lukashevich et Ag. Gorshkov, CHEMISTRY OF THOLEIITIC MAGMATISM AS RELATED TO THE EVOLUTION OF MIDOCEANIC RIDGES, Geotectonics, 23(06), 1989, pp. 550-555
The idea of tectonically homogeneous zones is used to study the relati
onship of variations in the composition of oceanic tholeiite basalts t
o the evolution of mid-oceanic ridges. A major element in classificati
on of tholeiite basalt glasses is presented, from which it follows tha
t low-Ti basalts poor in alkalis and rich in calcium (Type I) are conf
ined to areas formed during the initial 30 m.y. of the rift system, an
d to tectonically complicated ridge zones. High-Ti basalts enriched in
alkalis and depleted in calcium (Type III) occur in rift zones that h
ave undergone more than 80 to 90 m.y. of evolution since the basalts w
ere extruded. In terms of their composition and relationship to durati
on of rift zone evolution, Type-II basalts are transitional.