GEOCHEMICAL CRITERIA FOR THE RIFT ORIGIN OF THE PLIOCENE-PLEISTOCENE BASALTS OF THE EASTERN SIKHOTE ALIN

Abstract

To obtain more complete petrological information, we thoroughly studied volcanic rocks of the Sovetskaya Gavan complex in the Koppi River basin on the Sovetskaya Gaan' Plateau and along upper reaches of the Samarga River in the northwestern part of the Samarga Plateau. Petrographically, rocks of this complex are fairly uniform. They are dominated by basalt and doleritic basalt. Our petrologic data do not support the possibility of assigning the basaltic rocks of the Sovetskaya Gavan' complex either to the trap association of platforms, or to the alkalic olivine basalts. The systematic drop in alkali content of evolving basalt magma, as well as the suboceanic nature of the youngest extrusives are the distinguishing features of igneous complexes of continental rifts with spreading rates greater than 1 cm per year.