| 1. |
- Ernst, R. E., et al.
(författare)
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The 1501 Ma Kuonamka Large Igneous Province of northern Siberia : U-Pb geochronology, geochemistry, and links with coeval magmatism on other crustal blocks
- 2016
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Ingår i: Russian Geology and Geophysics. - : GeoScienceWorld. - 1068-7971. ; 57:5, s. 653-671
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Tidskriftsartikel (refereegranskat)abstract
- A new large igneous province (LIP), the 1501 ± 3 Ma Kuonamka LIP, extends across 700 km of northern Siberia and is linked with coeval dikes and sills in the formerly attached Sao Francisco craton (SFC)-Congo craton to yield a short-duration event 2000 km across. The age of the Kuonamka LIP can be summarized as 1501 ± 3 Ma (95% confidence), based on 7 U-Pb ID-TIMS ages (6 new herein) from dolerite dikes and sills across the Anabar shield and within western Riphean cover rocks for a distance of 270 km. An additional sill yielded a SIMS (CAMECA) age of 1483 ± 17 Ma and sill in the Olenek uplift several hundred kilometers farther east, a previous SIMS (SHRIMP) age of ca. 1473 Ma was obtained on a sill; both SIMS ages are within the age uncertainty of the ID-TIMS ages. Geochemical data indicate a tholeiitic basalt composition with low MgO (4-7 wt%) within-plate character based on trace element classification diagrams and source between E-MORB and OIB with only minor contamination from crust or metasomatized lithospheric mantle. Two subgroups are distinguished: Group 1 has gently sloping LREE ((La/Sm)PM = 1.9) and HREE ((Gd/Yb)PM = 1.8) patterns, slightly negative Sr and moderate TiO2 (2.2 wt%), and Group 2 has steeper LREE ((La/Sm)PM = 2.3) and HREE ((Gd/Yb)PM = 2.3), strong negative Sr anomaly, is higher in TiO2 (2.7 wt%), and is transitional from tholeiitic to weakly alkaline in composition. The slight differences in REE slopes are consistent with Group 2 on average melting at deeper levels. Proposed reconstructions of the Kuonamka LIP with 1500 Ma magmatism of the SFC-Congo craton are supported by a geochemical comparison. Specifically, the chemistry of the Chapada Diamantina and Curaga dikes of the SFC can be linked to that of Groups 1 and 2, respectively, of the Kuonamka LIP and are consistent with a common mantle source between EMORB and OIB and subsequent differentiation history. However, the coeval Humpata sills and dikes of the Angola block of the Congo craton represent a different magma batch.
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| 2. |
- Grinko, A. A., et al.
(författare)
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Sediment Organic Matter in Areas of Intense Methane Release in the Laptev Sea : Characteristics of Molecular Composition
- 2020
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Ingår i: Russian Geology and Geophysics. - 1068-7971 .- 1878-030X. ; 61:4, s. 456-477
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Tidskriftsartikel (refereegranskat)abstract
- We present results of study of the molecular composition of organic matter (OM) in the bottom sediments of the Laptev Sea by gas chromatography-mass spectrometry, isotope gas chromatography-mass spectrometry, and Rock-Eval pyrolytic analysis. The OM of all collected sediment samples shows a significant terrigenous contribution. Compounds that are biomarkers of methanotrophic microorganisms arc also found. A positive correlation between the contents of the studied biomarkers and the contents of pelite and total organic carbon is observed at the sites with documented intense methane bubbling. For example, the average content of C30 hopenes at the methane stations is twice higher than that at the background ones. The average content of C32 alpha beta-hopanes in sediment samples from the methane seepage area is 1.5 tunes higher than that at the background stations. We suggest that the increased C30 alpha beta-hopane content (similar to 1.5 times higher within the methane seepage area) and the decreased more index relative to the C31 hopane index are due to the inflow of OM of petroleum origin. The presence of biphenyl in sediments indicates its petroleum origin, which supports our assumption of the migratory nature of petroleum hydrocarbons in the methane seepage area. Triterpenoids found in the sediment OM indicate diagenetic bacterial transformation of OM in the methane seepage areas, which shows that methane has been released for a long time. We assume the intense activity of the consortium of methanotrophs and sulfate reducers in the methane seepage areas.
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| 3. |
- Ledneva, G. V., et al.
(författare)
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Late Triassic siliceous-volcano-terrigenous deposits of the Chukchi Peninsula : composition of igneous rocks, U-Pb age of zircons, and geodynamic interpretations
- 2016
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Ingår i: Russian Geology and Geophysics. - : GeoScienceWorld. - 1068-7971 .- 1878-030X. ; 57:8, s. 1119-1134
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Tidskriftsartikel (refereegranskat)abstract
- Study of Late Triassic volcanic, subvolcanic, and volcanosedimentary rocks of the Chukchi Peninsula (Vel'may terrane) has shown their different geochemical types. Basalts, dolerites, and tuffs of the lower-middle strata of the Upper Triassic section bear evidence for their formation in suprasubductional geodynamic setting. Basalts and dolerites of the upper strata of this section correspond in composition to within-plate rocks and are similar to Middle-Late Triassic oceanic-plateau basalts and dolerites. U-Pb dating of magmatic zircons from tuffs of the lower-middle strata and from dolerites of the upper strata shows the almost synchronous magmatic activity in the suprasubductional (206 +/- 5 Ma) and within-plate (212 +/- 4 Ma) geodynamic settings. (C) 2016, V.S. Sobolev IGM, Siberian Branch of the RAS.
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| 4. |
- Mekhonoshin, A. S., et al.
(författare)
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Relationship between platinum-bearing ultramafic-mafic intrusions and large igneous provinces (exemplified by the Siberian Craton)
- 2016
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Ingår i: Russian Geology and Geophysics. - : GeoScienceWorld. - 1068-7971. ; 57:5, s. 822-833
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Tidskriftsartikel (refereegranskat)abstract
- This study aims at summarizing available geological and geochemical data on known Proterozoic platinum-bearing ultramafic-mafic massifs in the south of Siberia. Considering new data on geochemistry and geochronology of some intrusions, it was feasible to compare ore-bearing complexes of different time spans and areas and to follow their relationships with the recognized large igneous provinces. In the south of Siberia, the platinum-bearing massifs might be united into three age groups: Late Paleoproterozoic (e.g., Chiney complex, Malozadoisky massif), Late Mesoproterozoic (e.g., Srednecheremshansky massif), and Neoproterozoic (e.g., Kingash complex, Yoko-Dovyren massif, and massifs in the center of the East Sayan Mts.). In most massifs but Chiney the initial magmas are magnesium-rich. On paleogeodynamic reconstructions, the position of the studied massifs is the evidence that three most precisely dated events in North Canada continued into southern Siberia: In the period 1880-1865 Ma, it was the Ghost-Mara River-Morel LIP; at 1270-1260 Ma, the Mackenzie LIP; and at 725-720 Ma, Franklin LIP. In Siberia, the mostly productive massifs with respect to PGE-Ni-Cu mineralization are those linked with the Franklin LIP: Verkhny Kingash, Yoko-Dovyren, and central part of the Eastern Sayan Mountains, e.g., Tartay, Zhelos, and Tokty-Oy.
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| 5. |
- Pikovsky, Y. I., et al.
(författare)
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The block structure and the presence of oil and gas in the Siljan impact crater
- 2017
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Ingår i: Russian Geology and Geophysics. - : Elsevier. - 1068-7971 .- 1878-030X. ; 58:2, s. 199-205
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Tidskriftsartikel (refereegranskat)abstract
- Morphostructural modeling of the block structure of a part of the Scandinavian crystalline shield has shown that the ring structure of the Siljan Ring impact crater is located in the center of a morphostructural node, a ring structure with a diameter of 300 km, marking a large disjunctive tectonic knot. The crater area consists of a central block, which is a granite massif, and of a surrounding mobile morphostructural boundary forming a wide small-block ring depression zone, where oil and gas shows have been revealed within the crater. This zone is regarded as the most promising one for search for migration channels and atypical shows of hydrocarbons.
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