20_6

Volume 20, 6, 2001

Geophysics and Tectonics
Yu. F. Malyshev.Types of the earth's crust in East Asia, and their geological interpretation 3
K.Zh. Seminsky.Tectonophysical regularities of the lithospheric destruction as exemplified by the Himalayan compression zone 17
A.A. Sorokin. The Paleozoic accretionary complexes of the eastern segment of the Mongolian-Okhotsk fold belt 31

Volcanism
Yu.A. Martynov and D.U. Li. Late Mesozoic-Cenozoic basaltic volcanism in Korea 37
V.P. Simanenko. Mid-Jurassic volcanites of the eastern part of the Partizansk coal basin (Primorye) 50

Sedimentology
V.N. Svalnov. The oceanic manganese micronodules as indicators of sedimentation conditions 57

Metallogeny
M.V. Goroshko, G.B. Solomatin, and V.V. Nikolaev. Experience in the use of aerogamma-spectrometric survey for metallogenic zoning of the southeastern part of the Siberian platform 70
N.A. Borodkin and V.A. Pristavko. Geological-geochemical characteristics of the Ekug-Tumaninsky ore field (Chukotka) 88
I.D. Petrenko, N.M. Bolshakov, V.A. Gumenyuk, and A.A. Poletaeva. Mineralogical, geochemical and paleohydrogeochemical zoning of the Mutnovskaya ore field (Kamchatka) 103

Chronicles
G.L. Kirillova. The Third Symposium IGCP 434 109

Reviews
V.A. Buryak. Fundamental research devoted to the geology of placers and metallogeny 116
N.I. Filatova and V.S. Vishnevskya.The Cretaceous in Eastern Russia: sedimentation, geodynamics, biodiversity, and climate 120

Anniversaries
Ye.A. Kulish (70-th birth anniversary) 121
V.A.Stepanov (60-th birth anniversary) 122

Index of papers published in the journal in 2001 123

Yu. F. Malyshev
Types of the earth's crust in East Asia, and their geological interpretation

A scheme is constructed showing types of the earth's crust in East Asia from the data of 49 regional and transregional seismic profiles (geotransects). There have been distinguished 6 types of the continental crust and 2 types of the transitional crust. As a result, the following has been established: 1. Evolutionary series of types of the crust from normal and high thickness and normal seismic velocity of the continental crust through that with the normal thickness and low velocity inside the continent to the thin crust with low velocity, and then to the transitional types of the crust at its Pacific margin. 2. Anomalous characteristics of tectonic elements of the crust as compared to the world data. 3. Contrasting parameters of the relict and newly formed crust in the major sedimentary basins (the Vilyui Syneclise, Songliao, the North China one) and in the Yakutia diamond-bearing province. This indicates a transformation of large volumes of the continental crust affected by the Pacific plates.

K.Zh. Seminsky
Tectonophysical regularities of the lithospheric destruction as exemplified by the Himalayan compression zone

Regularities of recent structure formation in Central Asia are discussed on the basis of tectonophysical concepts of division of the volume under deformation into blocks by faults of variable orientations that are characterized by length, depth and width. A map of the zone-block structure of the lithosphere has been compiled for the region under study; it shows blocks contacting with each other in wide zones of destruction that are distinguished by high density of faults and associated earthquakes. From results of the analysis of geometrical sizes and degrees of activity of destructive zones, a strict hierarchy of destruction is revealed; within the limits of the continent the Himalayan zone of interaction of the Indostan and Eurasian plates has been mapped as the 1st rank target for further detailed research. It is established that the zone-block structure of the Himalayan zone resulted from the evolution of the fault zones that merged at a certain stage of the rank development to create a uniform network and, therefore, were transformed into destructive zones. The latter develop or are re-activated under substantial impact of movements of separated blocks. Thus, the main regularities of structure formation of the Himalayan compression zone, which have been established by the analysis of the zone-block structure, are in agreement with the results obtained earlier basing on the concepts of viscous flow of the substratum under loading in this region and provide additional specific details. From the quantitative processing of seismological and, in part, geological and structural data, generalized percentage ratios have been defined for contribution of elementary dynamic settings into the formation of the internal structure in the zones of compression, extension, shear, compression with shear, and extension with shear. According to these ratios, the Himalayan zone of destruction is formed under compression with shear. This, in distinction from the clearly manifested transpression, is predetermined by the indentor character of the inheritedly developing contact of the two lithospheric plates. Destructive zones of the 2nd and 3rd ranks, included in the paragenesis of compression proper, are localized at the northern and southern boundaries of the Himalayan zone; by orientation, peculiarities of the internal structure and the pattern of dynamic settings of their formation, these zones suggest that the Himalayan zone is mature, with its active axis of stress tensor being inclined. The paragenesis of the strike-slip fault involves its central and, largely, eastern parts, showing the well-known process of the material transfer from the area of the highest compression to the frontal boundary of the Indostan block. In general, the character of the lithospheric destruction is controlled not only by (1) the intensity and direction of the external impact, (2) structure, composition and dimensions of the volume under deformation, but also by (3) the laws of active interaction of blocks and destructive zones with each other. Major laws are the existence of spatial-temporal irregularity of the process, which is directly reflected in the temporal and spatial variations of the degree of activity and dynamic settings even in the homogeneously loaded volumes, and also the rank hierarchy of the zone-block lithospheric structure.

A.A. Sorokin
The Paleozoic accretionary complexes of the eastern segment of the Mongolian-Okhotsk fold belt

In the modern structure of the eastern part of the Mongolian-Okhotsk fold belt fragments of Paleozoic subduction complexes are distinguished. Some of them accreted to the southern margin of the North Asia craton; while the others, to the continental blocks of the Late Paleozoic Amur superterrane. The accretionary complexes of the opposite continental margins are separated by the Lower Mesozoic turbidite formations reflecting the last stage of existence of the Mongolian-Okhotsk paleooceanic basin.
In the history of closure of the Mongolian-Okhotsk Ocean a possibility of repeated functioning of subduction zones along the converging margins of the North Asia craton and the Amur superterrane is shown. By the beginning of the Mesozoic such subduction processes resulted in the formation of complex accretionary and fold structures along those margins.

Yu.A. Martynov and D.U. Li
Late Mesozoic-Cenozoic basaltic volcanism in Korea

A summary of the published geological and geochemical information on the Late Cretaceous-Cenozoic magmatism on the Korean Peninsula shows a regular change of geochemical features of basaltic magmas in the Cenozoic from typically subduction (Late Cretaceous) to typically intraplate features (Quaternary). Proceeding from this, the existence of two major magmatic sources is suggested - the subduction and intraplate sources. According to geochemical and isotope data, the intraplate source was localized within the bounds of the heterogeneous subcontinental lithosphere and exerted a determining influence on the composition of different age basalts. The contribution of the subduction component into magma genesis diminished at the Cenozoic boundary, which is along with the change in the character of volcanism from mainly felsic to mainly basic and with a shift of the latter toward the eastern and northeastern parts of the peninsula gives grounds to suggest a change in the tectonic regime of the region development at the beginning of the Paleogene, cessation of subduction, and onset of rifting. Together with the earlier published information on the East Sikhote-Alin volcanogenic belt, these data are indicative of the necessity to correct the existing concepts of tectonic evolution of the Eurasian continental margin in the Cenozoic, of the age and mechanism of opening of the Japan Sea basin.

V.P. Simanenko
Mid-Jurassic volcanites of the eastern part of the Partizansk coal basin (Primorye)

The mid-Jurassic assemblages of the Monakinskaya suite in the Partizansk coal basin, Primorye, are made up of coal-bearing deposits, volcanites, and subvolcanic rocks. Volcanites are represented by rhyolites; and subvolcanic rocks, by dacites and rhyodacites. Chemically, the magmatic rocks of the suite are close to volcanites of the marginal-continental volcanic belts of the Pacific continental framing developed on the thick continental crust. With respect to the character of the deposits, composition, age and geodynamic position, they are best correlated with magmatites of the North Korea Late Jurassic-Early Cretaceous belt.

V.N. Svalnov
The oceanic manganese micronodules as indicators of sedimentation conditions

On the basis of comprehensive investigations of protosyngenetic manganese micronodules it is shown that they are formed mainly at the water-sediment interface, and have a short history of formation. They are very sensitive to changes of the environment, sedimentation rate, and conditions of syngenesis. These changes are adequately reflected in the micronodule composition in the moment of their incipience, that is, micronodules are a reliable target for investigation of sedimentation conditions.

M.V. Goroshko, G.B. Solomatin, and V.V. Nikolaev
Experience in the use of aerogamma-spectrometric survey for metallogenic zoning of the southeastern part of the Siberian platform

As exemplified by the southeastern part of the Siberian platform, a possibility in principle of application of results of aerogammaspectrometric survey is shown for a preliminary metallogenic zoning of the poorly studied territories with respect to rare and radioactive elements (U, Zr, Ta, Nb, Tr, Mo, and others) on the basis of processing aerogammspectrometric data and specification of structural-tectonic constructions from interpretation results of aeromagnetic and gravity fields.
Large metallogenic subdivisions of three metallogenic epochs have been discriminated: Early-Late Proterozoic, Late Paleozoic, and Late Mesozoic Tyrkan-Maimakan ore-bearing system, and Aim-Aldan and Tyrkanda ore-bearing areas. In turn, smaller metallogenic subdivisions are identified within their bounds: ore districts, clusters and fields. The metallogenic specific character of the ore districts, clusters and fields has been determined.

N.A. Borodkin and V.A. Pristavko
Geological-geochemical characteristics of the Ekug-Tumaninsky ore field (Chukotka)

The geological composition of the famous in Eastern Chukotka Ekug-Tumaninsky ore field with tin and gold-antimony mineralization is described. By the results of geological-geochemical research the following was established: an assemblage of 28 elements, the level of the local geochemical background and the indicator role of every element with respect to tin, gold and polymetallic mineralization; the anomalous character of the Ekug -Tumaninsky ore field with respect to Au, W, Sb, Sn, As, Pb, Zn, Ag, Mo, Bi, Li and Be: four characteristic geochemical assemblages: tin-rare metal, arsenic-rare metal, polymetallic and gold-antimony; geochemical structure of the Ekug-Tumaninsky ore field where three smaller structures are distinguished: tin-rare metal, gold-antimony and tungsten - polymetallic taxons; concentric lateral zonation in the distribution of the basic metals Sn ® Au ® W in the ore filed; and the genetic relationship of tin, gold and tungsten mineralization caused by crystallization of the metal-bearing hypabyssal intrusion.

I.D. Petrenko, N.M. Bolshakov, V.A. Gumenyuk, and A.A. Poletaeva
Mineralogical, geochemical and paleohydrogeochemical zoning of the Mutnovskaya ore field (Kamchatka)

The interrelationships between mineralogical and geochemical zoning of gold-and-silver polymetallic mineralization are considered. It is associated with the Pliocene-Early Pleistocene paleovolcanic structure. Basing on the study of gas-liquid inclusions and a paleovolcanic analysis, reconstructions of the geomorphological and hydrogeochemical setting during ore formation have been performed, and conclusions have been made on its genesis, which explain the reason for the referred zoning.
The hydrothermal system formed after cessation of active volcanism. At the initial stages its parameters were determined by the temperature regime of the cooling near-surface peripheral magmatic chamber; as a result, silver-polymetallic ores were forming with a distinct lateral concentric zoning. As the chamber was cooling, structural factors were brought to the forefront; late-stage mineralization is formed in the zones of substantial dislocations, and is cross-cutting with respect to the early zonal system.