Volume 21, 3, 2002
|
Volume 21, 3, 2002 |
|
A.A. Sidorov. Ore formations and metallogenic zoning of the Pacific Belt 3
A.N. Derkachev, I.A. Tararin, Ye.P. Lelikov, A.V. Mozherovskiy, Y.Grainert, N.N. Barinov. Manifestation of low-temperature hydrothermal activity in the backarc basin, Okhotsk Sea (Kuril deep-sea basin) 14
L.V. Eirish, V.A. Stepanov. The platinum content of the Far East: zoning, objective regulations, and problems 27
G.Z. Gilmanova, L.A. Maslov, R.G. Kulinich, O.S. Komova. Geodynamics of the earth's crust in the Taiwancollision zone 40
V.M. Grannik.Paleoseismofocal zones of Sakhalin 50
Byung-Su Lee and Kwang-Soo Seo. Conodont bistratigraphy of the Mungog formation (Lower Ordovician), Yeongweol, Korea 66
B.I. Pavlyutkin, N.I. Belyanina.Quaternary deposits of Primorye: results of systematization and perspectives of study 80
P.I. Fedorov, N.I. Filatova, S.I. Dril, K.H. Chang, S.O. Park. Cenozoic volcanism in the southern part of Korea 94
G.V. Kharitonova, V.N. Zemlyanukhin , A.S. Manucharov, N.I. Chernomorchenko. Electronic-microscopic examination of Pb2+- Zn2+-saturated clay minerals 107
Anniversaries
Georgy Mikhailovich Vlasov (to the 90-th anniversary) 119
A.A. Sidorov
Ore formations and metallogenic zoning of the Pacific Belt
Zones of epithermal mineralization are connected mainly with the close physical-chemical (volcanogenic) conditions of ore formation and seem to be peculiarly qualitative; numerous breaks of uniformity in both internal and external zones are determined chiefly by metallogenic inheritance as a result of rejuvenation of metal-bearing formations.
A.N. Derkachev, I.A. Tararin, Ye.P. Lelikov, A.V. Mozherovskiy, Y.Grainert, N.N. Barinov
Manifestation of low-temperature hydrothermal activity in the backarc basin, Okhotsk Sea (Kuril deep-sea basin)
Mineralogy and geochemistry of the low-temperature hydrothermal formations developed on the surface of basalts and in their fractures on a submarine volcano in the north-eastern part of the Kuril deep-sea basin have been studied. The following order of distinguishing of mineral phases has been established: Fe-rich sulphides (pyrite) - Fe-rich layered silicates (hydromica of celadonite - nontronite type) - amorphous silica (opal) - Fe-oxyhydroxides (goethite) - Mn-oxyhydroxides (vernadite). The sulphide mineralization is of phenocryst-stockwork type. The finding of pure barite fragments does not exclude presence of the hydrothermal "smokers" on this volcanic structure.
L.V. Eirish, V.A. Stepanov
The platinum content of the Far East: zoning, objective regulations, and problems
A review of platinoid ore and placer occurrences in the Russian Far East was done. Zones and areas of potentially platinum-bearing intrusions and regions of possible "black schist" ore mineralization are specified and briefly characterized. Platinoid occurrences are noted in connection with gold ores in brown coals, etc. Commercial platinoid placers, including large ones (Kondyor), are associated with basite-ultrabasite intrusions.
Ore deposits of platinoids in the Far East have not yet been detected. To raise the prospective effectiveness, it is recommended that the petrological and geochemical study of rock complexes potentially promising for platinoids be stepped up, and the analytical base and the methods of platinoid extraction from ores of complex deposits be improved.
G.Z. Gilmanova, L.A. Maslov, R.G. Kulinich, O.S. Komova
Geodynamics of the earth's crust in the Taiwan collision zone
Based on the results of recent geophysical research carried out in the Pacific Oceanology Institute, gravity modeling has been done and the geodynamic state of the earth's crust has been predicted along the latitudinal profile (~21.5°N) stretching from the West Philippine basin to the South China Sea and crossing the Gagua, North Luzon and Hengchong Ridges, and also the North Luzon trough and the northern termination of the Manila trench. The results obtained allow the conclusion that many peculiarities of contemporary geodynamics in so active a region are determined by its own density inhomogeneities. Geodynamic calculations accord with tectonic and geophysical characteristics of the main morphostructures in the region. Particularly, the earlier conclusion that the Gagua Ridge formed as a result of tectonic piling-up of the earth's crust and the eastern slope of the North Luzon Ridge is in the state of active compression. The observed directions of the rate vectors of masses displacement there are indicative of the process of isostatic compensation of this morphostructure. According to calculations, the zone of juncture of the North Luzon Ridge and the North Luzon trench is an area of substantial strike-slip deformations, which corresponds to one of the main tectonic boundaries of the region. Generally, the geodynamics of the region is determined by the relaxation of the mantle bulge in the West Philippine basin, and leveling of the density boundaries in the gravity field. Comparison of the results of the joint analysis of the geoid height and bathymetry with mechanical calculation results shows that an analogous objective regularity is traced in the vector field of masses viscous movement.
V.M. Grannik
Paleoseismofocal zones of Sakhalin
Brief characteristics of structural elements of the Early Cretaceous and Late Cretaceous-Paleogene active Pacific margins are given. The essence of the notions "seismic focal zone" (Benioff zone) and "paleoseismic focal zone" (Benioff paleozone, subduction suture) is specified. Benioff zones correspond to a subducting part of the oceanic plate. They are represented by one or several zones of the geological medium continuity located at the boundaries or inside the subducting plate caused by mechanical dislocations of rock and thermal fluid masses, phase transitions (structural and material transformations) of rocks of the subducting plate and its interaction with the subasthenospheric mantle. In folded belts Benioff paleozones are represented by subduction sutures fixing blocking of subsidence of oceanic plates and disappearance of the earlier active Benioff zones. Pre-Mesozoic Benioff paleozones can also be included into zones of folding. The Central Sakhalin Benioff paleozone (a zone of melanged large-block mixites and ophiolite melange 65-70 km wide, dipping west at 13-56°) and the Okhotsk Sea Benioff paleozone (a zone of ophiolite melange 40-70 km wide, dipping west at 45°) included into the Early Cretaceous and Late Cretaceous-Paleogene active margins are reconstructed. The geological structure of the island and adjacent water areas in the Late Mesozoic-Early Cenozoic formed in the course of subsequent development of the characterized different-age active margins.
Byung-Su Lee and Kwang-Soo Seo
Conodont bistratigraphy of the Mungog formation (Lower Ordovician), Yeongweol, Korea
Three sections (Golmacha, Seonghwangchon, and Mohari sections) of the Mungog Formation, Yeongweol, are examined for conodont biostratigraphy. Assemblage Zone 1 (=Semiacontiodus nogamii - Cordylodus lindstroem -Utahconus beimadaoensis Zone), Assemblage Zone 2 (=Rossodus manitouensis - Chosonodina herfurthi Zone), Assemblage Zone 3 (=Scolopodus quadraplicatus-Paroistodus proteus - Drepanoistodus forceps Zone), and Assemblage Zone 4 (=Paracordylodus gracilis Zone are tentatively established within the formation. The preliminary data on correlation of these zones are briefly summarized. The Cambrian - Ordovician boundary in the Yeongweol area is probably present within beds immediately below Assemblage Zone 1, near the base of the Mungog Formation.
B.I. Pavlyutkin, N.I. Belyanina
Quaternary deposits of Primorye: results of systematization and perspectives of study
Debatable problems of the Quaternary deposit stratigraphy of Primorye are discussed. Critical analysis of the earlier adopted unified scheme of division of the Quaternary deposits (Decisions…, 1987) and distinguished regional horizons is given. We have cast doubt on the belonging of the Nakhodkinsky and Lazovsky horizons to the first and second steps of the Upper Neopleistocene, respectively. Comprehensive study of the sections of the South Primorye coastal area (from drilling data) allowed us to distinguish the Golubovskaya suite composed of two subsuites: lower, pebbled (aIII1gl1) and upper, clay-silt (amIII1gl2). We propose the stratotype of the suite, describe it, and give the evidence of its age. Correlation with other sections of this region has also been done. Based on the stratotype of the upper subsuite, we propose to distinguish the Golubovsky regional horizon (III1gl).
P.I. Fedorov, N.I. Filatova, S.I. Dril, K.H. Chang, S.O. Park
Cenozoic volcanism in the southern part of Korea
New data are offered on the strontium chemical and isotopic composition of Miocene (Pohang graben) and Pliocene-Quaternary (Cheju Island) volcanic complexes from the southern part of Korea connected with extension settings. The Early Miocene volcanics of the Yangnam zone are differentiated, from basalts to dacites, and are characterized by increased concentrations of high field-strength elements (HFSE) often exceeding those for E-MORB, by high Lan/Ybn ratios and a distinct Ta and Nb minimum, and also by the markedly varying values of 87Sr/86Sr=0.7041-0.7048, and according to data [Shimazu et al., 1990; Song et al., 1997], 143Nd/144Nd=0.512643-0.512843. The Middle Miocene basalts of the Pohang zone are distinguished by high alkalinity, high concentrations of LILE exceeding those for the oceanic island basalts (OIB) and close to the latter by HFSE contents. 87Sr/86Sr values in this group of rocks are close to those for the Early Miocene Pohang volcanics and range between 0.7044 and 0.7045; 143Nd/144Nd values vary between 0.512831 and 0.512845 [Shimazu et al., 1990; Song et al., 1997]. The Pliocene-Quaternary volcanics from Cheju Island are represented by alkaline basaltoids with insignificantly developed tholeiites, and also by trachytes. Basaltoids are noted for great enrichment in non-coherent elements, a stable Ta-Nb maximum, REE strong fractionation characterizing them as rocks of the intraplate alkaline series. Tholeiites from Cheju Island marked by LILE and HFSE high concentrations are distinguished by the varying behavior of the Ta-Nb anomaly. Tholeiites, alkaline basalts and trachytes are characterized by the variation interval 87Sr/86Sr=0.7040-0.7044.
Compositional variations of Cenozoic volcanics from the southern part of the Korea region allow a conclusion on the different nature of magma generating sources. For example, one relates the formation of the Early Miocene tholeiites of the Yangnam zone to mixing of the depleted and subduction components of the sources; the genesis of the Middle Miocene alkaline basalts of the P'ohang zone is determined by an intraplate source close to tholeiites from the Yangnam zone by their isotopic composition; the formation of the Pliocene-Quaternary basalts of Cheju Island is connected with mixing of the depleted and subduction components of the source.
G.V. Kharitonova, V.N. Zemlyanukhin, A.S. Manucharov, N.I. Chernomorchenko
Electronic-microscopic examination of Pb2+- Zn2+-saturated clay minerals
Saturation of montmorillonite and kaolinite in the 1 N Pb(CH3COO)2 solution is shown to result in the formation of a new metastable phase represented by hexagonal tabular electronically transparent monocrystals. Numerous crystals measuring up to 3 mm have been detected in montmorillonite preparations; and solitary crystals measuring up to 1mm, in kaolinite preparations. No changes in the particle organization of clay minerals have been registered in their saturation in the 1N ZnCl2 solution.