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1.
Doklady Earth Sciences - Dolerites of the parallel dikes formed in a back-arc spreading setting have been dated by Sm–Nd to the Silurian (426 ± 34 Ma) for Mount Azov in the Central...  相似文献   

2.
Previously published and new data on secondary transformations of the globular and platy phyllosilicates of the glauconite–illite series from the Upper Proterozoic terrigenous rocks of the Olenek and Anabar uplifts (East Siberia), Srednii Peninsula (Murmansk coast), and Vendian–Cambrian boundary rocks of the Podolian Dniester area (Ukraine) are generalized for the first time. Plastic deformation, aluminization, chloritization, berthierinization, as well as replacement of phyllosilicates of different morphology by corrensite- chlorite and pyrite at different lithogenesis stages, are considered and lithological-mineralogical characteristics of the glauconite-bearing rocks are reported. The structural, crystal-chemical, genetic, and isotopegeochronological features of di- and trioctahedral phyllosilicates are discussed.  相似文献   

3.
A new interpretation of the seismic profile series for the Taimyr Orogen and the Yenisei–Khatanga Basin is given in terms of their tectonics and geological history. The tectonics and tectonostratigraphy of the Yenisei–Khatanga and the Khatanga–Lena basins are considered. In the Late Vendian and Early Paleozoic, a passive continental margin and postrift shelf basin existed in Taimyr and the Yenisei–Khatanga Basin. From the Early Carboniferous to the Mid-Permian, the North and Central Taimyr zones were involved in orogeny. The Late Paleozoic foredeep was formed in the contemporary South Taimyr Zone. In the Middle to Late Triassic, a new orogeny took place in the large territory of Taimyr and the Noril’sk district of the Siberian Platform. A synorogenic foredeep has been recognized for the first time close to the Yenisei–Khatanga Basin. In the Jurassic and Early Cretaceous, this basin was subsided under transpressional conditions. Thereby, anticlinal swells were formed from the Callovian to the Aptian. Their growth continued in the Cenozoic. The Taimyr Orogen underwent tectonic reactivation and apparently right-lateral transpression from Carboniferous to Cenozoic.  相似文献   

4.
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5.
Zaika  V. A.  Sorokin  A. A.  Sorokin  A. P. 《Doklady Earth Sciences》2019,486(2):593-597
Doklady Earth Sciences - This paper presents the results of U–Pb (LA-ICP-MS) and Lu–Hf isotope studies of detrital zircons from the presumably Permian meta sedimentary rocks of the...  相似文献   

6.
Doklady Earth Sciences - It is shown that the giant Sikhote-Alin and Pamir deposits of boron are associated with fragments of the boron-bearing evaporite strata of paleoceanic atolls in the...  相似文献   

7.
The paper discusses the geochemical and Sr–Nd–Pb-isotope data on ice-rafted sediments (IRS) from different areas of the Arctic Ocean. Samples were collected during the Cruise of R/V Polarstern between Spitsbergen and North Pole, Yermak Plateau, as well as in Fram Strait. It is shown that the studied IRS samples in terms of LaN/YbN and εNd values are close to the composition of suspended particulate matter (SPM) from the mouth parts of large rivers and rivers transporting the sedimentary erosion products. This also follows from their Th/Sc, Th/Co, La/Sc, La/Sm, Sc/Th ratios and Sc content and from the position of their data points in the Sc–Th/Sc, La/Sc–Th/Co, and La/Sm–Sc/Th diagrams between the average SPM compositions of the Ob and Lena rivers. The values of 207Pb/206Pb and εNd in IRS samples give grounds to suggest that the rock complexes of the European, North American, and Asian continental margins could be potential sources for this sedimentary material. In the 207Pb/206Pb–εNd diagram, the IRS samples from all three studied areas define a compact cluster and are mainly confined to the triangle with corners represented by the Mackenzie River, Okhotsk–Chukotka volcanic area, and Lena River, being closer to the latter. In the Sm/Nd–εNd diagram, IRS points also form a compact field, being located almost in the middle between the average SPM compositions of the Yenisei and Ob rivers, on the one hand, and Lena River, on the other. In all diagrams, IRS samples from the different West Arctic areas show no significant scatter. With allowance for the fact that sediments are not subjected to significant homogenization during ice rafting, sediments from all three areas were obtained from a common source. As seen from the position of IRS data points in the 87Sr/86Sr–εNd diagram, this source was the Asian continental margin.  相似文献   

8.
Pudukkottai region in the northeastern part of the Madurai Block exposes the garnetiferous pink granite that intruded the biotite gneiss. Charnockite patches are associated with both the rock types. Rb–Sr biotite and Sm–Nd whole-rock isochron ages indicate a regional uplift and cooling at ～550 Ma. The initial Nd isotope ratios (\(\varepsilon _{\text {Nd}}^{\mathrm {t}}=-20\) to ?22) and Nd depleted-mantle model ages (TDM = 2.25 to 2.79 Ga) indicate a common crustal source for the pink-granite and associated charnockite, while the biotite gneiss and the charnockite within it represent an older crustal source (\(\varepsilon _{\text {Nd}}^{\mathrm {t}}= -29\) and TDM = > 3.2 Ga). The Rb–Sr whole-rock data and initial Sr–Nd isotope ratios also help demonstrate the partial but systematic equilibration of Sr isotope and Rb/Sr ratios during metamorphic mineral-reactions resulting in an ‘apparent whole-rock isochron’. The available geochronological results from the Madurai Block indicate four major periods of magmatism and metamorphism: Neoarchaean–Paleoproterozoic, Mesoproterozoic, mid-Neoproterozoic and late-Neoproterozoic. We suggest that the high-grade and ultrahigh-temperature metamorphism was preceded by magmatism which ‘prepared’ the residual crust to sustain the high P–T conditions. There also appears to be cyclicity in the tectono-magmatic events and an evolutionary model for the Madurai Block should account for the cyclicity in the preserved records.  相似文献   

9.
The ages of the two main stages of carbonate cover formation within the Tuva–Mongolian microcontinent have been determined. The Pb–Pb age and Sr–chemostratigraphic characteristics of the carbonate rocks of the Irkutnaya, Agaringol, and Zabita formations, as well as of the Zabita Formation phosphorite, demonstrate that the first stage began in the Middle Riphean (Late Ectasian) at about 1290 Ma and the second stage started in the Early Vendian (Early Ediacaran) at 630–600 Ma. The accumulation of phosphorite deposits started in the Ediacaran at about 580 Ma.  相似文献   

10.
The results of U–Pb geochronological studies of detrital zircons and Sm–Nd isotopic–geochemical studies of terrigenous rocks of the Upper Amur and Zeya–Dep troughs indicate that the beginning of orogenic processes, which led to the formation of the Mongol–Okhotsk fold belt, occurred in the Early Jurassic.  相似文献   

11.
The close intergrowth of two native alloys of the compositions Ni0.59Cu0.24Al0.15Fe0.01Mn0.01 and Pd0.55Pt0.36Rh0.09 with a size of 10 μm has been discovered in the regolith from the Mare Crisium. A conclusion on its exhalative origin is made.  相似文献   

12.
The Karatau–Talas–Ferghana Fault (KTF) extending for 1500 km from Turgai to western Tarim is one of the world’s largest intracontinental strike-slip faults. This paper overviews the evolution of the KTF, providing insight into its relatively poorly studied northern segment in the Karatau Range and Turgai, known as the Main Karatau Fault (MKF). The right-lateral strike-slip along the KTF developed during three stages in the late Permian–Triassic, Early–Middle Jurassic, and late Cenozoic. The total strike-slip decreases northward from 200 km in the Ferghana Range to 100 km in the Karatau Range and decreases to zero in southern Turgai. Kinematic analysis of Jurassic grabens compensating the strike-slip in southern Turgai shows that strike slip along the KTF in the Jurassic, previously regarded as insignificant, actually measures tens of kilometers and 50% of the total strike slip in the northern segment of this fault.  相似文献   

13.
Doklady Earth Sciences - The morphology of archaeocyaths from the Oldynda Formation of the Uda–Vitim lithofacial zone and the Aikta Formation of the Birami–Yanguda Zone of West...  相似文献   

14.
Doklady Earth Sciences - Data indicating the important role of microorganisms in the redistribution of REEs in the weathering crust and the decisive role in the concentration of REEs during the...  相似文献   

15.
The Zhuxi deposit is a recently discovered W–Cu deposit located in the Jiangnan porphyry–skarn W belt in South China. The deposit has a resource of 3.44 million tonnes of WO3, making it the largest on Earth,however its origin and the evolution of its magmatic–hydrothermal system remain unclear, largely because alteration–mineralization types in this giant deposit have been less well-studied, apart from a study of the calcic skarn orebodies. The different types of mineralization can be classified into magnesian skarn, calcic skarn, and scheelite–quartz–muscovite(SQM) vein types. Field investigations and mineralogical analyses show that the magnesian skarn hosted by dolomitic limestone is characterized by garnet of the grossular–pyralspite(pyrope, almandine, and spessartine) series, diopside, serpentine,and Mg-rich chlorite. The calcic skarn hosted by limestone is characterized by garnet of the grossular–andradite series, hedenbergite, wollastonite, epidote, and Fe-rich chlorite. The SQM veins host highgrade W–Cu mineralization and have overprinted the magnesian and calcic skarn orebodies. Scheelite is intergrown with hydrous silicates in the retrograde skarn, or occurs with quartz, chalcopyrite, sulfide minerals, fluorite, and muscovite in the SQM veins.Fluid inclusion investigations of the gangue and ore minerals revealed the evolution of the ore-forming fluids, which involved:(1) melt and coexisting high–moderate-salinity, high-temperature, high-pressure(>450 ℃and >1.68 kbar), methane-bearing aqueous fluids that were trapped in prograde skarn minerals;(2) moderate–low-salinity, moderate-temperature, moderate-pressure(~210–300 ℃and ~0.64 kbar),methane-rich aqueous fluids that formed the retrograde skarn-type W orebodies;(3) low-salinity,moderate–low-temperature, moderate-pressure(~150–240 ℃and ~0.56 kbar), methane-rich aqueous fluids that formed the quartz–sulfide Cu(–W) orebodies in skarn;(4) moderate–low-salinity,moderate-temperature, low-pressure(~150–250 ℃and ~0.34 kbar) alkanes-dominated aqueous fluids in the SQM vein stage, which led to the formation of high-grade W–Cu orebodies. The S–Pb isotopic compositions of the sulfides suggest that the ore-forming materials were mainly derived from magma generated by crustal anatexis, with minor addition of a mantle component. The H–O isotopic compositions of quartz and scheelite indicate that the ore-forming fluids originated mainly from magmatic water with later addition of meteoric water. The C–O isotopic compositions of calcite indicate that the ore-forming fluid was originally derived from granitic magma, and then mixed with reduced fluid exsolved from local carbonate strata. Depressurization and resultant fluid boiling were key to precipitation of W in the retrograde skarn stage. Mixing of residual fluid with meteoric water led to a decrease in fluid salinity and Cu(–W) mineralization in the quartz–sulfide stage in skarn. The high-grade W–Cu mineralization in the SQM veins formed by multiple mechanisms, including fracturing, and fluid immiscibility, boiling, and mixing.  相似文献   

16.
It is shown that presence of the Early Precambrian sial crust in the Indo–Atlantic segment of the Earth and its absence in the Pacific has been caused by geochemical differences in the mantle underlying these segments. These differences were examined on the basis of Nd–Hf and U–Pb isotopes in modern basalts. The U–Pb isotope system is of particular interest, since uranium is a member of a group of heat-generating radioactive elements providing heat for plumes. It is shown that in the Indo–Atlantic segment, a distribution of areas of the modern HIMU type mantle is typical, while it is almost completely absent in the Pacific segment. In the Archean, in the upper HIMU type paleo-mantle areas, plume generation and formation of the primordial basic crust occurred; this was followed by its remelting resulting in the appearance of an early sial crust forming cratons of the Indo–Atlantic segment.  相似文献   

17.
In this article we present geochemical and isotope characteristics of rocks of the Unerikan, Selitkan and Aezop–Yamalin volcano–plutonic zones of the eastern termination of the Mongol–Okhotsk Orogenic Belt. The obtained data demonstrate that the Mesozoic igneous rocks of the Mongol–Okhotsk sector of the Pacific Folded Belt were formed due to the melting of the continental crust in a tectonic setting corresponding to a suprasubduction one.  相似文献   

18.
Kumar  Neeraj  Narayan  J. P. 《Natural Hazards》2019,97(2):747-774
Natural Hazards - The variation of 2D fundamental frequency of stand-alone structure on rock $$ ({F}_{{02{\text{D}}}}^{\text{S}} ) $$ and in a basin $$ ({F}_{{02{\text{D}}}}^{\text{BS}} ) $$ with...  相似文献   

19.
Recent interpretation of seismic sections and free-air gravity anomalies in offshore northern Taiwan reveals that the southern Taiwan–Sinzi Folded Zone began to form in late Middle Miocene, though it was mainly constructed in the Late Pliocene with strong reverse faulting and folding. Two westward progradational sequences were deposited in the shelf basin with sediments supplied from the southern Taiwan–Sinzi Folded Zone and the southern Ryukyu Arc. These two structures are displaced by several northwest-striking dextral strike–slip faults that were active in the early Quaternary when the clockwise-rotated southern Ryukyu Arc and the folded southern Taiwan–Sinzi Folded Zone were broken. It is believed that recent extension in the southern Okinawa Trough started in the early Quaternary because uplift on the southern Taiwan–Sinzi Folded Zone continued to latest Pliocene–early Quaternary. Paleogene–Miocene sediments of the East China Sea Shelf in the western part of the southern Okinawa Trough Basin are interpreted to indicate that the East China Sea Shelf Basin extended to the east of the southern Taiwan–Sinzi Folded Zone.  相似文献   

20.
The first results of SHRIMP dating of magmatic complexes and associated gold–silver deposits and ore occurrences (Kupol, Dvoinoe, Moroshka, and others) in the Chukotka sector of the Russian Arctic coast are discussed. The petrological and isotopic–geochronological data are used for reconstructing their formation conditions.  相似文献   

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