PHYSICOCHEMICAL CONDITIONS OF IRON-TITANIUM OXIDE FORMATION IN ROCKS OF THE KONDER ALKALIC ULTRAMAFIC PLUTON

Abstract

Olivinite was developed in the emplacement front of clinopyroxenite and gabbro, and its thickness is directly proportional to the combined thickness of these clinopyroxene-bearing rocks. Oxidation of dunite olivine and the resulting formation of olvinite could have occurred within a narrow fO2 range (10-2 to 10-5) upon cooling below temperatures of 550° to 530°C. The variation in fluid regime of dunite-oxidizing clinopyroxenite and gabbro upon such cooling, as reflected in the evolution of iron-titanium oxide compositions, is described by the curve derived from an equation given in the paper. Consequently, these clinopyroxene-bearing rocks would have oxidized dunite only if their temperature has been no lower than 800°C, and that of the dunite no higher than 550°C. The process that produced olivinite should be classified as one of high-temperature metasomatic alteration at the contact between two physico-chemically contrasting rock media. Overall, the data seem to support the restite model of emplacement of the Kondyor pluton, even if they are regarded as semiquantitative.