Geochemical structure of the Yoko-Dovyren layered dunite-troctolite-gabbro-norite massif, northern Baikal area

The application of the principle and algorithm of the cluster analysis of rock compositions in magmatic complexes, which were described elsewhere, made it possible to reveal the spaceless and spatial geochemical structure of the Yoko-Dovyren layered mafic-ultramafic massif. The diversity of rocks composing this intrusion was demonstrated to comprise eleven discrete geochemical types (clusters): dunites, harzburgites, melanotroctolites, troctolites, two types of olivine gabbro, two types of olivine gabbronorites, quartz gabbronorites, and granophyres. These geochemical types of rocks and the corresponding fractionation parameters (the iron atomic fraction f of mafic minerals and the anorthite concentration An of plagioclase) define a succession corresponding to the tendencies in the crystallization of a magma of respective composition. This geochemical succession is in complete agreement with the succession in which rocks were formed in the intrusion (from dunite in its bottom part to quartz gabbronorites and granophyres near its roof) and is complicated by cyclical repetitions. The main tendency revealed in the cyclic layering is as follows: cyclical intercalations consist of rocks corresponding to the neighboring members of the rock succession (plagiodunites and melanotroctolites, melanotroctolites and troctolites, troctolites and olivine gabbro, olivine gabbro and olivine gabbronorites). These tendencies are closely similar to those identified in the Kivakka intrusion, a fact suggesting that these tendencies can be common for all layered complexes of mafic and ultramafic rocks.[PUBLICATION ABSTRACT]