EVOLUTION OF THOLEIITIC BASALT VOLCANISM OF THE EASTERN PACIFIC

Abstract

We conducted a special study of tholeiite volcanism of the eastern Pacific, using multivariate statistical methods. It was based on our own and published analyses of samples obtained in deep-sea dredging and drilling in the region that extends from the Explorer and the Juan de Fuca Ridges on the north to the Eastern Fracture Zone on the south, including the Galapagos Rift Zone on the east. Isolated diagram fields extending both vertically and horizontally are formed by basalt samplings from the Galapagos spreading zone and the Explorer zone. To interpret them, we consider the distribution of rare-earth elements (REE) in the rocks. Analysis of relevant data shows that REE concentration curves, normalized relative to carbonaceous chondrites, are approximated by a straight line, and therefore are characteristic of original rock compositions depleted in light REE. Rocks with more iron have a higher overall REE-concentration level, as revealed by their higher ytterbium content. This trend of compositional variability of basalts is specific in each of the zones studied.