Volume 19, 4, 2000
|
Volume 19, 4, 2000 |
|
Petrology, Mineralogy and Geochemistry
L.N.Khetchikov, V.A.Pakhomova, V.K.Popov, A.A.Chashchin, V.I.Sapin.Composition of melted inclusions in minerals and temperature regime of rock formation, Dikiy Greben Volcano (Kamchatka) 3
A.B.Osipenko, L.P.Anikin, Yu.M.Stefanov.Rodingites of the Kamchatka Cape, Eastern Kamchatka 12
S.V. Rasskazov, A. Boven, A.V. Ivanov, V.G. Semenova.Middle Quaternary volcanic impulse in the Olekma-Stanovoy mobile system:40Ar-39Ar dating of volcanics from the Tokinsky Stanovik 19
A.Yu. Antonov. On the genesis of the mafic shliroid inclusions in the Late Mezozoic granitoids of the Aldan Shield south boundary (the Stanovoy Range) 29
G.N.Gamyanin, Yu.Ya.Zhdanov, V.G.Moiseenko. Natural and man-made mineral spheroids 52
G.G.Shcheka, N.I.Ekimova. On genetic nature of the native osmium in ferroplatinum 61
Sedimentology and Stratigraphy
M.N. Shapiro, A.V. Lander, N.P. Chamov. Genesis of sialic clastics in the Eocene-Oligocene formations of Northeast Kamchatka: implication for geodynamics of the Komandorsky Basin, the Bering Sea 66
A N. Filippov, I.V. Kemkin, E. S. Panasenko.Early Jurassic hemipelagic deposits of the Samarka terrane (Central Sikhote-Alin): structure, composition and sedimentary environments 83
Yu.D.Markov, A.V.Mozherovsky, N.N.Barinov, N.A.Sereda. Layered silicates of green clayey formations from the shelf sediments of the recent Ilse des Cenders Volcanoes (South China Sea)97
I.B. Tsoy, V.V. Shastina. Cenozoic siliceous microplankton assemblages in the Terpeniya Rise deposits (the Okhotsk Sea) 105
E.L. Shkolnik, E.A. Zhegallo. New results on SEM investigation of grain phosphorites from the Pesca Locality, Columbia 116
Metallogeny
P.V.Komarov. Metallogenic cycle and geochronological mineralization epoch in a matter-genetic and time classification of hydrothermal deposits 123
L.N.Khetchikov, V.A.Pakhomova, V.K.Popov, A.A.Chashchin, V.I. Sapin
Composition of melted inclusions in minerals and temperature regime of rock formation, Dikiy Greben Volcano (Kamchatka
Data on peculiarities of Dikiy Greben Volcano rocks (southern Kamchatka) and characteristics of mineral-forming inclusions in their minerals are presented. X-ray spectroscopy showed high SiO2 contents (more than 71 wt%) in silicate glasses of all the study inclusions, and peculiarities of other oxides concentration in them. In all probability, the inclusions preserved residual liquors. Irrespective of the rock basicity, the SiO2- content is high in a matrix glass as well (often 78 wt%). The concentration of other components is close to that of the mineral-impregnations. Thus, a total rock composition is determined by the composition of minerals-impregnations. Evolution of temperature regime during crystallization of mineral-impregnations in a magmatic chamber has been studied using homogenization of melted inclusions.
A.B.Osipenko, L.P.Anikin, Yu.M.Stefanov
Rodingites of the Kamchatka Cape, Eastern Kamchatka
New data on peculiarities of geological setting and composition are presented for contact calc-silicate metasomatites – rodingites, associated with serpentinized ultramafics of the Kamchatka Cape Peninsula ophiolite complex. Morphology of occurrences, chemical and mineralogical composition of the studied metasomatites are similar to analogous from different ophiolite complexes of Eastern Kamchatka. As proposed, process of rodingitization has a distinct two-staged character. At the early stage, high-temperature interaction occurred, followed by calcium saturation of protoliths. The last-stage epigenetic mineral alteration was isochemically proceeded (except for the hydroxyl-ion enter) and represented mainly by successive substitution of initial H2O-free mineral assemblages to H2O-bearing mineral paragenesises.
S.V. Rasskazov, A. Boven, A.V. Ivanov, V.G. Semenova
Middle Quaternary volcanic impulse in the Olekma-Stanovoy mobile system: 40Ar - 39Ar dating of volcanics from the Tokinsky Stanovik
40Ar-39Ar ages of volcanic rocks from the Tokinsky Stanovik were determined by total laser fusion of a matrix. An interval of dates obtained is between 0.59 and 0.28 Ma and represents a singlevolcanic impulse. The initial and final eruption products of the latter were basanite hawiites. More alkaline lavas of the basanite, phono-basanite and olivine melanephelinite compositions dominated the middle stage of volcanic activity. Volcanism was controlled by reactivation of a weakened zone of the Stanovoy suture. Variations in magmatic conduit orientations indicate a change of tectonic stress during the volcanic activity. Eruptions commenced under northeast compression and westeast extension in the crust. An anti-clockwise rotation of a tensional tensor was accompanied with volcanic eruptions enveloped a larger area. Volcanism finalized under westeastern compression and northsouthern extension. It is suggested that volcanism in the Tokinsky Stanovik was initially triggered by compressional forces derived from the North American-Eurasian collision zone and afterwards developed due to the compressional stress created in the collision zone between the Izu-Bonin and Honshu arcs.
On the genesis of the mafic shliroid inclusions in the Late Mezozoic granitoids of the Aldan Shield south boundary (the Stanovoy Range)
Amongdiver se inclusions in the granitoids from the Stanovoy Range, fine-grained mafic inclusions, in which SiÎ2 content varies from gabbro to quartz diorites (even within separate accumulations) with the predominance of the basites and having the specific “needle” magmatic structures are of great importance. These inclusions, as compared to the enclosed granitoids, appeared to be more melanocratic. Their mineral composition suggests that they crystallized at high temperatures and pressures, but the contents of fo2, CH2Î, and PH2Î are very close and have similar or increased concentrations of alkali sum, K,Rb, Pb, Ba and more often similar concentrations of TiÎ2, P2Î5, H2Î, B, F, Li, Be, Sn, Zn, i.e. the components usually accumulating in the latest leucocratic products of the granitoid magma differentiation, most enriched in volative components. Because of their composition similarity to the region basalt-andesitic volcanics it might be proposed that they are genetically associated with the crust high temperature mafic (mainly alkali) upper mantle magmas rather than with low temperature crust granitoid magmas. Most probably, as the result of the different degree interaction and mixture of these contrast magmas, the largest part of the magmatic products of the intermediate composition and the “drop-similar” formations (shliroid inclusions) in the mafic magmas were formed. The inclusions came to the surface due to their rather high saturations of bubbles and quickly crystallized in the conditions of the similar fo2, regime of the volative components and, accordingly, the tendency to the diffusion smooth of the compositions of the interacting magmas.
G.N. Gamyanin,Yu.Ya. Zhdanov, V.G. Moiseenko
Natural and man-made mineral spheroids
The paper presents data on an unusual spheroidal form of minerals established in gold ore hydrothermal mineral occurrence and similar man-made spheroids. The paper also considers species diversification of the spheroids, which are represented by free and intermetallic phases, oxide and sulphide formations together with their surface and inner structure, mineral phase composition constituting natural and man-made spheroids. Some typical differences between natural and man-made mineral spheroids are given.
On genetic nature of the native osmium in ferroplatinum
The investigation of widespread plate inclusions in grains of the ferroplatinum showed that part of these belongs to relics of the earlier iridosmin-osmirid phases, enriched in Ru. Others are thin (lesser than 100mm) and net- like composed of a pure osmium (more than 96 wt% Os). We consider it to be a result of a breakdown of solid solution of osmium in the ferroplatinum. As to the authors’ opinion, it is due to limited miscibility at the Pt-Os range, which decreases along with the iron-enriched platinum. The compositions suffered to solid solution decay are near Pt9Fe with Os content above 1.3 at.% in enclosed platinum. The highest solubility of osmium within the studied composition of platinum (according to square measurements of the osmium plates) reaches as much as 14 at% of Os. The regularities above are sufficiently supported by the experimental investigations on the solubility of Os at the Pt.
M.N. Shapiro, A.V. Lander, N.P. Chamov
Genesis of sialic clastics in the Eocene-Oligocene formations of Northeast Kamchatka: implication for geodynamics of the Komandorsky Basin, the Bering Sea
The Eocene-Oligocene terrigenous rocks with relatively high content of acid clasts (granite, rhyolite and quartz) are very common in the southwest of the Karaginsky Island and Govena Peninsula (Northeast Kamchatka). These rocks are considered as a part of an accretionary prism formed above the NW-dipping subduction zone. To the northeast from the continent, basalts and tuffs of the Govena volcanic arc and Eocene-Oligocene terrigenous rocks of its train are developed. But there are almost absent acid rocks, and a sialic component is low that enables to exclude this arc from the source of the sialic clasts in the coastal sediments. It is suggested that the accretionary prism was composed of the Eocene-Oligocene sediments accumulated in the eastern part of the Komandor basin at the foot of the Shirshov Ridge and transported to Kamchatka in the Miocene after the formation of a new spreading axis. The geodynamic reconstructions of the region for the Eocene-Miocene are represented
A. N. Filippov, I. V. Kemkin, E. S. Panasenko
Early Jurassic hemipelagic deposits of the Samarka terrane (Central Sikhote-Alin): structure, composition and sedimentary environments
The results of lithologic, petrographic and biostratigraphic investigations of hemipelagic cherty-argillaceous rocks of ancient oceanic plate sedimentary cover are presented. They are widespread as fragments in the Samarka terrane of Middle-Late Jurassic accretionary wedge (Central Sikhote-Alin). These rocks are Late Plinsbachien-Early Toarcian in age and consist of clayey radiolarian red cherts, brown and grey-greenish radiolarian siliceous mudstones and silty mudstones. Hemipelagic sediments were accumulating at the areas located near the intraplate oceanic volcanic rises of the alkaline basalts that were the main provenance. They are distinguished by the volcanic ash layers that indicate that the explosive volcanism was active along the convergence zone, and most likely are evidence of an episode of the subduction rate rise.
Yu.D.Markov, A.V.Mozherovsky, N.N.Barinov, N.A.
Layered silicates of green clayey formations from the shelf sediments of the recent Ilse des Cenders Volcanoes (South China Sea
Distribution and mineral composition of green clayey sedimentary formations (the moulds of test cavities of foraminifers, globules and clay rock fragments) were studied in the area of the recent Isle des Cendres Volcanoes. The rise of iron hydroxides was established in the sediments of northwestern volcano foot during the activation of this volcano and near tectonic dislocations.
Cenozoic siliceous icroplankton assemblages in the Terpeniya Rise deposits (the Okhotsk Sea
Siliceous microplankton assemblages (radiolarians, diatoms, and silicoflagelates) recovered from the Terpeniya Rise lower sedimentary cover are ifferent in age. The oldest ones identified in amudstone layer consist of poorly- preserved radiolarians and sporadic marine diatoms and it was dated within a wide time interval from the Paleocene to Early Eocene from the pollen data. Three zonal diatom and radiolarian assemblages were identified in the tuffaceous diatom layer. These are 1 - the latest Oligocene/Early Miocene (the diatom Thalassiosira praefraga Zone, the radiolarian assemblage Lipmanella japonica conica-Gondwanaria dogieli); 2 – the latest Early Miocene (the diatom Crucidenticula kanayae Zone, the radiolarian Calocycletta costata Zone), 3 - the diatom Denticulopsis praelauta Zone, the radiolarian Calocycletta costata Zone). It is inferred that Cenozoic marine sedimentation emerged within both the Yuzhno-Okhotsk Basin and West Kamchatka at the same time, i.e. in Paleocene.
New results on SEM investigation of grain phosphorites from the Pesca Locality, Columbia
The grained phosphorites from the Pesca Locality of the Eastern Cordillera (Columbia) were studied in detail using SEM. The phosphorites are typical for the Late Cretaceous phosphorite-bearing system of Venezuela, Columbia, Ecuador and Peru. Phosphate grains are often composed of foraminifer tests (about 30 % of the grain volume). The grains composed of fragments of calcareous sponges (class Inosoa) and microbial mats were observed for the first time (all together make up 50-60 % of the grain volume). The presence of phosphate oncolites (up to 15 %), oncolite coatings on the grains, and phosphatized cement from the microbial mat was proved. Phosphorites of the studied area show an extremely close resemblance to the coeval phosphorites of North Africa (especially Morocco, Algeria and Tunis) in the type of biological remains. Phosphorites of the Pesca Locality can be classified as deposits formed by the combination of the re-washed and accumulated, originally phosphatized sediments of the outer shelf and subtidal-intertidal zones.
Metallogenic cycle and geochronological mineralization epoch in a matter-genetic and time classification of hydrothermal deposits
The concept of metallogenic cycle of mineralization is under consideration. The relationships between plutonic, volcanogenic, and amagmatogenic cycles and tectono-magmatic stage (megacycle) of minaralization have been established. Geochronological mineralization epoch has been characterized, and its relationships with etallogenic cycle and metallogenic epoch are studied. Role of geochronological epoch as a egularly structured period (from a stage to an epoch or vice versa) and a standard for estimation of polychronous mineralization of deposits, ore fields and regions, is substantiated. It is shown that metallogenic cycle and geochronological epoch of ineralization are the final more complex regular mineral units and formation periods that along with other units of matter-genetic and time classification reflect the peculiarities of hydrothermal deposits.