Chemical composition of rocks and minerals from the Mid-Atlantic Ridge near 15°20'N

The monograph summarizes results of petrological and geochemical studies of rocks from the ocean floor collected by the authors during expeditions to the Central Atlantic. Detailed work in the Capa Verde transform fault zone gave a large amount of new information about magmatic and hydrothermal systems of the Mid-Atlantic Ridge.

(Table 1.15) Composition of glassy basalts from the north part of the Bougault anomaly, Mid-Atlantic Ridge 15°N

Structure and composition of sub-surface bottom sediments from the southwest Barents Sea have been under study. The study has revealed heterogeneity of sediment structure resulted from temporal irregularity and variability of sedimentation processes. The study of the heavy minerals from 0.1-0.01 mm grain size fraction has shown prevalence of green hornblende, epidote, garnet, and ilmenite in all types of sediments; these minerals are the basis of terrigenous-mineralogical province. At the same time in different areas local terrigenous-mineralogical associations have been identified. Clay mineral composition of in the sediments was quite uniform: biotite, chlorite, hydromica, smectite. Despite this, a number of features indicating initial stages of clay mineral transformation has been identified. Differences in material composition and structure of the studied sediments are associated with rapid change in paleogeographic situation on the land - ice cover melting on the Kola Peninsula and subsequent Holocene climatic situation.

Composition of basalts from the north part of the Bougault anomaly, Mid-Atlantic Ridge 15°N

A quantitative model of development of magmatic and ore-magmatic systems under crests of mid-ocean ridges is constructed. Correct physical models of melting zone formation in approximation to active spreading, non-stationary dynamics of magma intrusion from a center of generation, filling of magma chambers of various shapes, feeding of fissure-type volcanoes, and retrograde boiling of melts during solidification of intrusive bodies beneath axial zones of spreading in crests of ridges are proposed. Physicochemical and mathematical theories of disintegration of multi-component solutions, growth of liquational drops of ore melts, and sublimation of components from magmatic gases are elaborated. Methods for constructing physically correct models of heat and mass transfer in heterophase media are devised. Modeling of development of magmatic and ore-magmatic systems on the basis of the Usov-Kuznetsov facies method and the Pospelov system approach are advanced. For quantitative models numerical circuits are developed and numerical experiments are carried out.

Mineral, chemical and isotope compositions of clay subfractions from formations of the Srednii Peninsula, Murmansk coast of the Barents Sea

Fine-grained clay subfractions (SFs) with particle size of <0.1, 0.1-0.2, 0.2-0.3, 0.3-0.6, 0.6-2.0, and 2-5 µm separated from claystone of Upper Precambrian Pumanskaya and Poropelonskaya formations on the Srednii Peninsula were studied by transmission electron microscopy, X-ray diffraction, and Rb-Sr methods. All subfractions consist of low-temperature illite and chlorite, and contribution of chlorite decreases with diminishing particle size. The crystallinity index and I002/I001 ratio increase from coarse- to fine-grained SFs. Leaching by ammonium acetate solution and Rb-Sr systematics in combination with mineralogical and morphological data indicate that illite in Upper Proterozoic claystone from the Srednii Peninsula formed during three time intervals: 810-830, 610-620, and about 570 Ma ago. The first generation of this mineral with low Rb/Sr ratio dominates in coarse-grained SFs while the second and third generations with a high Rb/Sr ratio prevail in fine-grained SFs. All of three generations are known in Poropelon claystone, whereas Puman claystone contains only illite of the first and second generations. Geological processes responsible for multistage illite evolution in claystones are discussed.