Early Mesozoic age of protolites of metasedimentary rocks from the Tukuringra terrane in the Mongolian–Okhotsk fold belt: Results of LA–ICP–MS U–Pb geochronological studies

2017 ◽  
Vol 474 (1) ◽  
pp. 542-545
Author(s):  
A. A. Sorokin ◽  
B. Xu ◽  
A. P. Sorokin ◽  
V. A. Zaika ◽  
Yu. V. Plyaskin
2019 ◽  
Vol 486 (4) ◽  
pp. 446-450
Author(s):  
V. A. Zaika ◽  
A. A. Sorokin ◽  
A. P. Sorokin

This paper presents the results of U–Pb (LA–ICP–MS) and Lu–Hf ­isotope studies of detrital zircons from metasedimentary rocks of the Tokur Terrane. It has been shown that metasedimentary rocks of the Tokur and Ekimchan formations are characterized by similar age peaks of detrital zircons, which indicates a close (or same) age of these formations. The lower age of the sedimentation is determined by the age of the youngest zircons of 326–323 Ma. The upper age boundary is determined of 254–251 Ma, based on the intruded of the Late Permian granitoids. The main sources of zircons in the metasedimentary rocks of the Tokur Terrane are the igneous and metamorphic complexes of the southeast framing of the North Asia Craton. The Tokur Terrane can be considered as a fragment of the Paleozoic accretionary complex, the formation in front of the southeastern margin of the North Asia Craton.


2019 ◽  
Vol 484 (6) ◽  
pp. 734-738
Author(s):  
R. O. Ovchinnikov ◽  
A. A. Sorokin ◽  
A. B. Kotov ◽  
E. B. Sal'nikova ◽  
V. P. Kovach ◽  
...  

The results of studies indicate that the age of the protoliths of garnet-bearing biotite–sericite–muscovite schists of the Inim Block is <991 Ma, and they are derived from rocks of the Neo-, Meso-, and Paleoproterozoic (as well as Archean) crust. This suggests that the Inim Block is exotic relatively to the Argun Superterrane due to the formation of the protolith of its metasedimentary rocks largely from erosion products of the Early Precambrian continental crust, the presence of which within the Argun Superterrane is not proven. It is not excluded that the Inim Block is a fragment of the Dzhugdzhur–Stanovoi Superterrane implanted in the structure of the Argun Superterrane as a result of Mesozoic tectonic events.


2019 ◽  
Vol 484 (4) ◽  
pp. 455-459
Author(s):  
V. A. Zaika ◽  
A. A. Sorokin ◽  
V. P. Kovach ◽  
A. P. Sorokin ◽  
A. B. Kotov

The results of the U—Th—Pb geochronological studies indicate that in the Un’ja-Bom terrane the youngest peaks on the relative probability curves of ages are 207 and 212 Ma for zircons from the metasiltstone of the Kurnal formation and from the metasiltstone of the Amkan formation. Similar age estimates for the youngest peaks were obtained for the detrital zircons from the metasedimentary rocks of the Tukuringra terrain of the eastern part of the Mongol-Okhotsk belt, which indicates that the Lower Mesozoic flyschoid complexes in the structure of this belt are developed much wider than is currently believed. The results obtained in our U—Th—Pb geochronological and Sm—Nd isotope geochemical studies suggest’s that the sedimentary rocks material was carried to the sedimentation basin mainly from the continental massifs of the Amur superterrane.


2019 ◽  
Vol 484 (4) ◽  
pp. 472-477
Author(s):  
A. V. Chugaev ◽  
I. V. Chernyshev ◽  
A. E. Budyak ◽  
G. V. Mandzhieva ◽  
A. S. Sadasyuk ◽  
...  

The isotopic composition of uranium is a new geochemical indicator that facilitates reconstruction of the redox conditions of geological processes. In this paper the results of study of the 238U/235U isotope ratio in the Neoproterozoic metasedimentary rocks of the Baikal–Patom fold belt (Northern Transbaikalia) were obtained using the MC-ICP-MS method and 233U+236U double spike. The scale of 238U/235U ratio variations (δ238U = –0.37 to –0.11‰) is within the range of (–0.39 to +0.15‰), typical of metasedimentary terrigenous rocks of marine origin. In terms of the δ238U values, uranium of the BPB rocks studied is heavier than seawater uranium (δ238U = –0.41 ± 0.03). There is a correlation between the δ238U value in the rocks and their position in the stratigraphic section. Variations of the 238U/235U ratio in the terrigenous-carbonate sequences of BPB indicate that the sedimentation conditions changed and euxinic conditions were established in the course of evolution of the paleobasin in the Late Ediacarian Period.


2021 ◽  
Vol 40 (3) ◽  
pp. 16-27
Author(s):  
V.A. Zaika ◽  
◽  
A.A. Sorokin ◽  

The article presents detrital zircon U-Th-Pb and Lu-Hf isotope data for metasedimentary rocks from the eastern Tukuringra Terrane, as well as whole-rock Sm-Nd isotope data. Our analyses show that the zircons in metasedimentary rocks are mostly early Mesozoic in age. Early Paleozoic and Neoproterozoic zircons are also common, whereas early Precambrian zircons are virtually absent. The age of the youngest zircon population places a lower age limit on the age of the Tungalin Formation at 204 Ma (Late Triassic, Rhaetian), the Dugda Formation at 181 Ma (Early Jurassic, Toarcian), and the Tangomen Formation at 189 Ma (Early Jurassic, Pliensbachian). Essentially all Mesozoic, Paleozoic and Neoproterozoic zircons are characterized by Neo- and Mesoproterozoic Hf-model ages (tHf(DM) = 1.41–0.46 Ga, tHf(C) = 1.55–0.49) and Mesoproterozoic Nd-model ages (tNd(DM) = 1.25–1.10 Ga, tNd(С) = 1.31–1.14). Our results suggest that sediments for deposition were sourced mainly from the continental Amuria Superterrane, but not from the southern margin of the North Asian Craton.


Author(s):  
Mikael Vasilopoulos ◽  
Ferenc Molnár ◽  
Hugh O’Brien ◽  
Yann Lahaye ◽  
Marie Lefèbvre ◽  
...  

AbstractThe Juomasuo Au–Co deposit, currently classified as an orogenic gold deposit with atypical metal association, is located in the Paleoproterozoic Kuusamo belt in northeastern Finland. The volcano-sedimentary sequence that hosts the deposit was intensely altered, deformed, and metamorphosed to greenschist facies during the 1.93–1.76 Ga Svecofennian orogeny. In this study, we investigate the temporal relationship between Co and Au deposition and the relationship of metal enrichment with protolith composition and alteration mineralogy by utilizing lithogeochemical data and petrographic observations. We also investigate the nature of fluids involved in deposit formation based on sulfide trace element and sulfur isotope LA-ICP-MS data together with tourmaline mineral chemistry and boron isotopes. Classification of original protoliths was made on the basis of geochemically immobile elements; recognized lithologies are metasedimentary rocks, mafic, intermediate-composition, and felsic metavolcanic rocks, and an ultramafic sill. The composition of the host rocks does not control the type or intensity of mineralization. Sulfur isotope values (δ34S − 2.6 to + 7.1‰) and trace element data obtained for pyrite, chalcopyrite, and pyrrhotite indicate that the two geochemically distinct Au–Co and Co ore types formed from fluids of different compositions and origins. A reduced, metamorphic fluid was responsible for deposition of the pyrrhotite-dominant, Co-rich ore, whereas a relatively oxidized fluid deposited the pyrite-dominant Au–Co ore. The main alteration and mineralization stages at Juomasuo are as follows: (1) widespread albitization that predates both types of mineralization; (2) stage 1, Co-rich mineralization associated with chlorite (± biotite ± amphibole) alteration; (3) stage 2, Au–Co mineralization related to sericitization. Crystal-chemical compositions for tourmaline suggest the involvement of evaporite-related fluids in formation of the deposit; boron isotope data also allow for this conclusion. Results of our research indicate that the metal association in the Juomasuo Au–Co deposit was formed by spatially coincident and multiple hydrothermal processes.


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