Volume 22, 2, 2003
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Volume 22, 2, 2003 |
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A.A. Sorokin, V.A. Ponomarchuk, S.K. Kozyzev, A.P. Sorokin, M.S. Voropaeva. New isotopic geochronological data for Mesozoic magmatic complexes of the North-Eastern margin of the Amur superterrane. 3
S.S. Zimin. Basite and ultrabasite massifs and related chromites; the features of their composition and nature. 7
F.P. Lesnov. Deep-seated xenoliths of ultramafites in alkali-basaltoid provinces: some specific features of REE geochemistry. 15
A.S. Zhitkov, G.I. Govorov. Tectonic control of the geochemical parameters of volcanites in the ocean-continent transition zone. 38
G.F. Ufimtsev. Order in the structure of tectonic relief of the transition zone in Eastern Asia. 44
N.T. Kochneva. The position of large ore districts in the orogenic structures of Central Chukotka (from data of morphostructural analysis). 49
B.M. Tishkin, L.N. Khetchikov, T.B. Afanasyeva, D.K. Kokorina, A.M.Kokorin. Recrystallization of quartz veined aggregates, and the problems of ore genesis. 57
S.M. Saprygin. Tectonic recurrence in the South and Middle Sakhalin entrails from instrumental data. 73
V.I. Isaev, N.V. Shpakova, O.S. Isaeva. The distributed bank of the geological and geophysical data on the oil and gas of the Sakhalin area. 81
Chronicles
F.À. Kuznetsov. Gaseous hydrates in ecosystem. 92
Anniversaries
N.A. Shilo (to the 90-th anniversary) 94
Obitueries
V.I. Sukhov (1931-2003) 95
V.A. Buryak (1932-2003) 97
A.A. Sorokin, V.A. Ponomarchuk, S.K. Kozyzev, A.P. Sorokin, M.S. Voropaeva
New isotopic geochronological data for Mesozoic magmatic complexes of the North-Eastern margin of the Amur superterrane
The paper presents new isotopic geochronological data for Mesozoic magmatic complexes of the north-eastern margin of the Amur superterrane obtained by the 40Ar/39Ar method. The age of the Early Cretaceous Upper Amur and Burinda intrusive complexes, Taldan and Gal’ka volcanic and subvolcanic complexes is specified. It is suggested to distinguish the Late Cretaceous trachybasalt-trachyanesite volcanic complex.
S.S. Zimin
The paper describes the peculiar occurrence of ultrabasite massifs, their shape, rock structure, and alteration of rocks with depth or from contact inward. Participation of komatiitic horizons, sometimes dikes and picritic lavas, and meimechites in ophiolitic volcanites of East Asia is also discussed. The increasing oxidation with depth of chromspinnelides is shown, which is related, like mass serpentization in ultrabasite and basite massifs, with the effect of post-magmatic fluids flowing along one or several channels underneath. This provides new possibilities for better understanding of genetic mineralogy of these magmatic rock bodies.
Basite and ultrabasite massifs and related chromites; the features of their composition and nature
F.P. Lesnov
Ultramafites from deep-seated xenoliths in all the known alkali-basaltoid provinces are abnormally and very non-uniformly enriched in light REE and some other highly incompatible elements as compared with similar rocks from continental massifs and mid-oceanic ridges. The non-uniformity of such enrichment is manifest both between different provinces and within one single province; quite often it is evident in an individual xenolith and even in individual grains of minerals. Data on REE content have been generalized in the paper, as well as data on other impurities and main components in the collection of 180 samples that characterize about 30 continental and insular alkali-basaltoid provinces. Such abnormal enrichment of ultramafites in light lantanoids is stipulated by the accumulation in them of epigenetic contaminate localized in the intergrain space, on the walls of microfractures and in the fluid inclusions in the minerals. An essential portion of the contaminate easily dissolves in the diluted solution of hydrochloric acid, which results in substantial reduction of REE content in the samples. In the analysis of bulk rock samples using contemporary methods, light REE included in the contaminate practically cannot be separated from structural impurity of light REE that is lower in concentration and is directly incorporated in the crystalline grid of the minerals. The conceptions prevail that abnormal enrichment of ultramafitic xenoliths is stipulated by the mantle metasomatism processes. Based on the analysis performed, the author arrived at the conclusion that such enrichment of ultramafites from xenoliths in light REE and other incompatible impurities is due to direct fluid introduction from the accommodating alkali basaltoids in the process of xenolith transportation from the upper-mantle magmatic chambers to the surface, rather than by the mantle metasomatism processes.
Deep-seated xenoliths of ultramafites in alkali-basaltoid provinces: some specific features of REE geochemistry
A.S. Zhitkov, G.I. Govorov
Data on the concentration of uranium, thorium, and potassium and K/U ratios in volcanic rocks at the juncture of the Kuril-Kamchatka and Japan arcs show similar geochemical parameters of lava from volcanoes of the Kuril-Kamchatka arc system of the Late Cretaceous and Quaternary stages of their development and different parameters of Quaternary lavas from the Japan and Kuril island arcs. This suggests that magma of these two arcs was generated in different tectonic settings: in an island-arc environment in the Kuril-Kamchatka arc and in a marginal continental environment in the Japan arc.
Tectonic control of the geochemical parameters of volcanites in the ocean-continent transition zone
G.F. Ufimtsev
The structure of tectonic relief of the continent-ocean transition zone in Eastern Asia is determined by a symmetrical composition of divisions characterized by ordered combinations of the forms comprising them. The nature of such a structure is considered in connection with the structure of the geoid relief and is recognized not only in the geodynamics of lithospheric plates but also in the interaction of the crustal and mantle segments of the Earth, essentially differing in density and thermal regime.
Order in the structure of tectonic relief of the transition zone in Eastern Asia
N.T. Kochneva
With the aid of morphostructural analysis and interpretation of space images, the structural sketch map of Central Chukotka has been developed. It can be used for reconstruction of the tectonic plan of the epoch of intensive mineralization. Within the limits of Central Chukotka, an arch uplift that is split by two tectonic axial zones is recognized. The longitudinal zone is of great ore controlling importance; almost all large deposits of the region are located in it. Ring-type and linear deformations have been detected in the arch uplift. Many of the ring-type structures are comparable with chamber structures that control mineralization. The complexly constructed ring structures with increased saturation in magmatic products are confined to the intersection of the greatest systems of orthogonal through faults. They determine the position of the largest ore districts.
The position of large ore districts in the orogenic structures of Central Chukotka (from data of morphostructural analysis)
B.M. Tishkin, L.N. Khetchikov, T.B. Afanasyeva, D.K. Kokorina, A.M.Kokorin
The degree of crystalline perfection (DCP) of quartz from veins of gold deposits has been correlated with the temperatures of decrepitation and homogenization of gas-liquid inclusions in it and with the chemical and mineral composition of quartz veined aggregates. Analogous work has been carried out with a quartz monocrystal. It has been shown that the DCS of quartz was significantly influenced by the composition of the substratum, from which quartz had been crystallized and recrystallized, and the power of the heat field created by veins and country rocks. Two trends have been outlined in the change of the degree of crystalline perfection with temperature: a reverse one for quartz veined aggregates, which underwent recrystallization, and a direct trend for monocrystals of quartz. This is due to two mechanisms of quartz formation: I –by crystallization and recrystallization of ore-bearing differently polymerized silicate fluid melts (solution melts), which in some cases experienced gelation; II – from hydrothermal solutions. The first mechanism is peculiar to the massive quartz of filling veins; and the second one, to formation of druses, «prisypki», pseudomorphs, etc.
Recrystallization of quartz veined aggregates, and the problems of ore genesis
The proposed model of magma differentiation in the geodynamic field specifies that ore generation starts at the subliquidus temperatures of the melt involving its viscous flow with the formation of a laminated structure in the magmatic chamber. Successive decompression of such a chamber in the tectonic process is responsible for successive filling of fractures with the melts similar in composition to the layers of the magmatic chamber. The migration of the melt along the fractures may be accompanied by its further differentiation. The model provides an explanation of the stages of mineralization and its relation with dikes including those of basic composition. It offers new opportunities for prediction of economic parameters of mineralization from data on the chemical composition of ore veins.
S.M. Saprygin
If geophysical, piezometric, geodetic and other instrumental data are used, then our notions of tectonic recurrence are changed. It appears that a sequence of tectonic events was realized in the South and Middle Sakhalin entrails during 75 years (1906-1981): strong earthquakes, horizontal movements, mud volcano eruptions and the Pacific plate subduction took place. This recurrence consists of two parts: a 72-year epoch of the entrails unloading by earthquakes, creep faults and mud volcano eruptions, and a three-year period of loading of the Eurasian plate margin by standing wave of horizontal compression.
Tectonic recurrence in the South and Middle Sakhalin entrails from instrumental data
V.I. Isaev, N.V. Shpakova, O.S. Isaeva
In the “Dalinformgeocenter”, on the basis of the integrated digital packets of the geological and geophysical data of oil-and-gas sedimentary basins, the distributed data bank of the Sakhalin area has been created. As the server of relational databases, the graphic system ArcView, communicating with heterogeneous DBMS has been used by the DBMS Oracle in the client part. The local computer networks created on the basis of structured cable systems are united through an isolated non-switched telephone pair. The transfer rate of the unified computer network makes 5-100 Mbit / sec.
The distributed bank of the geological and geophysical data on the oil and gas of the Sakhalin area
The internal means of the Oracle and ArcView create virtual representations of the users, and the transparency of arrangement of the data in the network is ensured, which solves the problems of redundancy and data integrity, and extremely simplifies the activity of the users with the data bank. The system provides updating of the databases «work project» - «current project», standardizes data, and the system of management of “all-round verification of access rights» ensures data protection.
The distributed data bank is the basic informational-and-analytical base of prediction of oil and gas potential of sedimentary basins and operational obtaining of miscellaneous information for controlling the entrails fund. The basic prospects for the development of the data bank involve piling up data of other sedimentary basins of the Far East region and creation the regional corporate computer network.