Том 24, № 2 (2016)

Mutual interaction of redox pairs resulting in the origin or decomposition of a metal phase is analyzed based on the concept of intrinsic oxygen fugacity. Reactions are suggested that may be responsible for the synthesis (or decomposition) of submicrometer-sized metal nuggets when experimental melts are quenched and can explain the possible crystallization of Pt—Fe alloys when basaltic melts cool and elucidate the nature of color of Au-bearing ruby glass. Possible disproportionation reactions of certain lower oxides into a higher oxide and respective metal in cooled silicate melts are discussed.

This paper presents a study of ongonites from the Chechek and Akhmirovo dike belts located within the Kalba—Narym batholith in Eastern Kazakhstan. The obtained conclusions are based on the investigations of melt and fluid inclusion in quartz phenocrysts, supplemented by mineralogical and geochemical data. It was established that the dike rocks were formed by crystallization of volatile-rich rare-metal melts in the presence of an aqueous fluid phase with subordinate amounts of carbon dioxide and methane. The ongonites crystallized from three geochemically different melts. Porphyritic phenocrysts in the ongonites of the Chechek and Akhmirovo dike belts crystallized at close temperatures 560–605°C and pressure of 3.6–5.3 kbar. Ongonite magmas that formed the Chechek and Akhmirovo dike belts had a high ore potential. However, degassing dynamics was not favorable for the development of metasomatism and formation of hydrothermal mineralization at the level of dike emplacement. The area of the rare-metal magmatism represented by ongonite dikes and rare-metal granite pegmatites has been distinguished in the northern part of the Kalba—Narym zone. The formation of rare-metal magmas was related to the differentiation in large granitoid chambers under the effect of juvenile fluids derived from the Tarim mantle plume.

This paper presents a study of Middle Paleozoic, Late Paleozoic, Early Cretaceous, and Early—Late Cretaceous granitoid complexes from two Pacific marginal seas. The granitoid complexes are subdivided into two large groups: (1) mantle-crust derivatives, including andesite differentiates, and (2) crustal palingenetic granites. In terms of formation depth, they are subdivided into abyssal, mesoabyssal, and hypabyssal granites, with decreasing depth from the old to young complexes. It was established that the granitoids of different genesis have peculiar geochemical features. The granitoids of distinguished genetic types differ in the content and proportions of alkalis, primarily, K, as well as Rb, Sr, and Ba. The palingenetic granites show the predominance of K over Na and are classified as high-K calc-alkaline rocks, whereas andesitic derivatives correspond to the calc-alkaline rocks. The former are characterized by the higher Rb and Ba contents, which is related to the geochemical affinity of these elements to K. In contrast, the Okhotsk Sea rocks are characterized by the predominance of Na over K, the elevated Sr content, and the lower Ba and Rb contents. In terms of geodynamic setting, the studied granitoids fall in the field of volcanic arcs and syncollisional rocks. The latters are represented by the palingenetic granitoids of the Sea of Japan.