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Vol 13, No 4 (2019)
- Year: 2019
- Articles: 7
- URL: https://journals.rcsi.science/1819-7140/issue/view/13150
Article
Postcollision Magmatism of Western Sector of the Mongol–Okhotsk Orogenic Belt: Oxidation Conditions and Metallogenic Zoning
Abstract
The Transbaikal sector of the Mongol–Okhotsk orogenic belt displays a well-consistent geochemical and metallogenic zoning. The axial zone of the belt, which is controlled by the Mongol–Okhotsk suture zone from the north, is composed of reduced ilmenite-series rocks. Tin, tungsten, and rare-metal deposits and occurrences previously distinguished by S.S. Smirnov as a rare-metal belt are confined to the ilmenite-series rocks. The reduced rocks are framed from the north and south by oxidized magnetite-series rocks with chalcophile mineralization. The distribution zones of the ilmenite-series rocks correspond to anomalies with lower gravity and magnetic fields, whereas the magnetite-series oxidized rocks correspond to anomalies with higher gravity and magnetic fields.
311-319
Sources of Sediment Clasts and Depositional Environment of the Upper Paleozoic Shazagaitui and Zhipkhoshi Formations of the Chiron Basin, Eastern Transbaikalia
Abstract
The article presents the results of comprehensive geological and geochemical study of the sedimentary rocks of the Upper Paleozoic Shazagaitui and Zhipkhoshi formations filling the upper part of the Chiron Basin, as well as U–Pb geochronological and Lu–Hf isotopic studies of zircons from these formations. The geochemical features of the terrigenous rocks of the Shazagaitui and Zhipkhoshi formations indicate that they were formed in a subduction zone environment. The presence of conglomerates and gravelstones and the predominance of unrounded and subrounded fragments in the rocks of the Shazagaitui and Zhipkhoshi formations also indicate their sedimentation in tectonically active zones. The abundant detrital zircons of Paleoproterozoic age, as well as the Paleoproterozoic and Archean Hf model ages of most of the zircons in the sandstones of the Shazagaitui and Zhipkhoshi formations, suggest that the main source of sediment clasts for these formations are the magmatic and metamorphic rocks of the southern surrounding of the North Asian Craton. However, the presence of Devonian–Carboniferous zircons with relatively young (mostly Neoproterozoic) Hf model ages is evidence that these zircons in the sedimentation basin were derived through erosion of mature (?) island arcs, but the contribution of this source is minor. The obtained results in combination with our regional geological data from previous studies suggest that the sediments of the Shazagaitui and Zhipkhoshi formations were accumulated in a basin setting on the southern framing of the North Asian Craton facing the Paleozoic Ocean.
320-340
On the Relative Age of the Late Cretaceous Zorin and Chingandzha Floras in the Northeast of Russia
Abstract
The Zorin and Chingandzha floras significantly differ in their systematic composition, but they are buried at the same stratigraphic level. On this basis, they are considered to be of the same age and are assigned to the Turonian–Coniacian period. The revealed features of the lithological composition of the plant-bearing deposits, their sequence, and the composition of the overlaying volcanic rocks indicate that both floras represent the first stage of the development of the outer zone of the Okhotsk–Chukotka Volcanic Belt. However, they are separated by one or two local geological events, and hence by a significant period of time. It can be confirmed that the Zorin flora was formed and existed earlier than the Chingandzha flora.
341-349
Concentrically-Zoned Massifs of the Tamanvayam Group (Koryak–Kamchatka Platiniferous Belt): Structure, Age, Petrological and Geochemical Aspects
Abstract
The paper presents new geological, petrological, and geochemical data on the dunite–clinopyroxenite–gabbro massifs of the Tamanvayam area. The time of formation of the intrusions is specified using U–Pb zircon dating. The Machevna Massif is mainly composed of gabbroids and clinopyroxenites, which are related by gradual facies transitions and intruded by amphibole gabbro, leucogabbro, and monzogabbro. The youngest rocks, cutting across all of the above-described varieties, are granites and granodiorites (tonalites), which make up composite injection bodies and small stocks in the central part of the massif. According to the new U–Pb dates, all of the intrusive rocks of the Machevna and Poputny intrusions were formed in a narrow time range of 73.1–67.7 Ma. The obtained range overlaps the formation interval of the siliceous volcanogenic sequences of the Achaivayam Formation (biostratigraphic studies, retrospective data). The geochemical similarity of the gabbroids and pyroxenites with intersecting amphibole gabbros and leuco- and monzogabbros allows us to attribute them to a single magmatic complex. The geochemical affinity and the penecontemporaneous formation of the intrusive rocks of the Tamanvayam area and volcanics of the Achaivayam Formation indicate their formation during a single tectonomagmatic event. At the same time, the gabbroids and pyroxenites can be considered as comagmatic rocks of the basalts and picrobasalts of the Achaivayam Formation. The high-Ca picrobasalts of the Achaivayam Formation that developed near the Machevna intrusion were presumably derived from parental melts of concentrically zonal massifs.
350-363
Improving Accuracy of Altimeter-derived Marine Gravity Anomalies for Geological Structure Research in the Vietnam South-Central Continental Shelf and Adjacent Areas
Abstract
In recent years, the satellite altimeter technology allows to enhance the marine investigation in any area. Up to now, many scientific studies have attempted to improve the accuracy and resolution of altimeter-derived gravity anomalies and have produced a gravity grid with interval of 1' × 1' for most the oceans all over the world. However, this gravity anomalies are not very high accuracy and have a large difference compared to shipboard gravity anomalies, especially in the coastal and islands areas. The purpose of this article is to improve the accuracy of altimeter-derived marine gravity anomalies for geological structure research in the Vietnam South-Central continental shelf and adjacent areas. The least squares collocation method is used to correct the altimeter-derived marine gravity data based on the shipboard gravity data in order to improve the accuracy of marine gravity anomalies. In this article, the altimeter-derived marine gravity anomalies are taken from Sandwell, D. T., et al., (V24.1) and the shipboard gravity anomalies are from the surveyed projects between Vietnam, Russia and other countries. Here, comparison of both those data has brought a mean-squared error is about ±9.358 mGal. After correcting, the mean-squared error between the corrected-altimeter-derived marine gravity and shipboard gravity anomalies are improved from ±9.358 to ±1.208 mGal (for the altimeter data coincided with shipboard track). Also, in this article, the Cenozoic sedimentary density and thickness are determined through the 3D interpretative methods of the above-corrected gravity anomalies in combination with seismic data. The achieved results realize how the efficiency and actuality of the corrected-altimeter-derived marine gravity anomalies for the detailed researches of geological structures. Especially, it is more meaningful in the remote or sparsely surveyed regions.
364-374
Lithochemistry Potential for Comparison and Correlation of Deposits on the Example of the Komsomolsk Section in Northern Sikhote-Alin, Far East of Russia
Abstract
The lithochemistry potential for comparison and correlation of terrigenous deposits and paleoreconstructions of facies sedimentation settings is studied on the example of the Komsomolsk section. The completed works and analysis of the first data on the contents of chemical components and values of lithochemical modules of the Upper Jurassic–Lower Cretaceous rocks making up the Komsomolsk section confirm the folded structure of this section previously identified by other methods. It is established that the layers of the southwestern and northeastern parts of the section are wings of a single syncline fold, while a “barren” sequence exposed in the northeasternmost part of the section lies at its base. The importance of combining different methods is noted.
375-389
First Findings of Early Cretaceous Foraminifera in the Lower Stream of Amur River, Khabarovsk Krai
Abstract
In southeastern Khabarovsk krai, in the basin of the Tumnin River, the foraminifera complex containing the characteristic species Ammosiphonia beresoviensis (Bulatova), represented by exclusively agglutinated shells, is revealed for the first time in sections of Albian deposits. In terms of composition and structure, the complex is closest to the associations widespread in the Albian in the Arctic paleogeographic zone. It differs from the coeval assemblages of Sakhalin and Japan in the absence of warm-water species.
390-395