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1.
用Y／Ho比值指示俄罗斯乌拉尔南部晶质菱镁矿矿床的成因   总被引：1，自引：1，他引：1  
乌拉尔省南部赋存有两种类型的晶质菱镁矿:1)白云岩地层中的层状矿体;2)白云质灰岩中的透镜状矿体。晶质菱镁矿矿体位于Riphean系列中下层的白云岩中,而在上层的白云岩单元中缺失。这两种类型的菱镁矿可通过矿体形态、晶体大小、石英和白云石含量不同来进行区分。第一种类型的菱镁矿储量巨大,菱镁矿呈粗粒结构,晶体粒径>10mm(最大达150mm);一般来说,矿体与白云岩围岩界限清楚,这种类型矿床以产在Riphean序列下部为特征。第二种类型的菱镁矿由于菱镁矿矿体穿插进入到白云岩围岩中,矿体很不规则,菱镁矿晶体也相对较小(1-5mm),这种类型的矿体主要产在Riphean中部层位中。这两种矿体都显示了交代成因的特征。但这两种菱镁矿矿石在一些主量元素和稀土元素的分布上具有不同的特征:与第二种类型相比,第一种菱镁矿具有较低的FeO,CaO和SiO2含量,与白云岩围岩(La／Lu>1)相比,具La／Lu<1的轻稀土亏损特征。第二种菱镁矿稀土分馏度较低,在稀土分配方面与白云岩围岩有差别。本文还特别讨论了Y／Ho值的重要性,因为该比值在菱镁矿和围岩中的类似性使得划分菱镁矿形成中的热液和成岩交代过程成为可能。因此我们认为,第一种类型菱镁矿,如具有高Y／Ho比值的Satka和Bakal矿床的形成属于沉积盆地发育过程中的早期成岩阶段;第  相似文献   

2.
In the Bashkir mega-anticline (western Urals) stratabound magnesite, siderite, fluorite and base-metal deposits are hosted by a sequence of Riphean sediments with a thickness of more than 12 km. The giant deposits of siderite (Bakal) and sparry magnesite (Satka) belong to the largest known mineral deposits of this type on Earth but are still disputed with respect to their origin. Both the Fe- and Mg-carbonate ores are clearly characterized by mimetic preservation of sedimentary and diagenetic textures of the host carbonate sediments, giving evidence of epigenetic metasomatic replacement. In the stratiform magnesite deposits of Satka, O- and C-isotopes, REE pattern and the lithostratigraphic position of the ore, point to the reflux of early diagenetic Mg-rich brines being responsible for the selective replacement of brecciated dolomite. The Bakal siderite deposits are hosted by Lower Riphean carbonate rocks and are controlled by a Lower to Middle Riphean unconformity marked by deep erosion and subsequent transgression-related sedimentation of coarse clastics. Their independence of carbonate lithofacies and their trace element distribution are indicative of metasomatic processes. Fe-bearing fluids have probably been generated by low-grade metamorphic (catagenetic) devolatization from underlying argillites, causing the metasomatic formation of large siderite ore bodies in the Bakal carbonates due to the focusing of the fluid flow by the overlying Mid-Riphean coarse clastics.  相似文献   

3.
For the first time, the age of magnesite in the Lower Riphean Bakal Formation of the Southern Urals is determined by the U—Pb (Pb—Pb) method: it is equal to 1366 ± 47 Ma (MSWD = 18). The stage of magnesite formation of the Bakal ore field was associated with the Mashak rifting pulse and took place prior to the formation of industrial deposits of the Bakal siderite.  相似文献   

4.
中—新元古代地层在南乌拉尔海槽中极为发育,地层厚度巨大,几个阶段的构造演化和沉积特征清晰可见。新太古代和下里菲是俄罗斯重要的大型层状铁矿和菱镁矿的宿主地层,中里菲群(元古宙地层)地层厚度极大,伴随了几次沉积旋回,发育了从深海相到大陆缓坡的碳酸盐岩沉积;随着新元古代末次冰期之后,文德系发育了可全球对比的白海动物群(伊迪卡拉动物群)。笔者首次确认了南乌拉尔地区中—新元古代地层3套臼齿构造,其中巴卡尔组(Bakal)碳酸盐岩臼齿构造与碎屑岩地震液化脉互层共生,特别是大量臼齿构造也发育在大型叠层石中。从臼齿构造与碎屑岩液化脉互层的共生特征,说明发育在碳酸盐岩中臼齿构造与地震机理的液化作用有关。该3套臼齿构造与中国华北地台中—新元古代地层中发现的臼齿构造(液化脉)时代大体接近。  相似文献   

5.
Results of the Rb–Sr and K–Ar isotopic dating of Riphean rocks from the southern Urals are discussed. Epigenetic transformation stages corresponding to 930, 525, and 750–800 Ma for Lower, Middle, and Upper Riphean, respectively, are recorded. These three rock groups presumably represented individual blocks, which experienced different secondary alterations.  相似文献   

6.
The formation of the Large Igneous Province (LIP) approximately 1380 Ma old in the South Urals was related to the Mashak riftogenic event in the Bashkir meganticlinorium, which was synchronous with the emplacement of different magmatic bodies (the Berdyaush pluton of rapakivi granites and associated rocks, the Main dike of the Bakal ore field, and the Medvedev, Guben, and Kusa massifs, among others) localized among sedimentary deposits of the Burzyan and Yurmatin Groups representing Lower and Middle Riphean type units of northern Eurasia. The U–Pb ID-TIMS age of 1379.6 Ma (MSWD = 1.3) obtained with an accuracy of ±2.9 Ma (confidence interval 95%) combined with the available published U–Pb ID-TIMS data constrain the age and duration of the Early–Middle Riphean pulse in the LIP formation in the Southern Urals.  相似文献   

7.
The stratiform base-metal Biksizak and Amur deposits, Kolpakovsky and Andree-Yul??evsky group of ore occurrences localized in the Eastern province of the Southern Urals and the adjacent Central Urals are considered in this paper. Their geology, composition of ore, and orebody morphology are characterized. These objects and occurrences occupy different geological positions, being hosted in (1) Ordovician, Silurian, and Devonian limestones formed in an island-arc setting (Biksizak deposit, Kolpakovsky occurrence); (2) Middle and Upper Devonian flyschoid sequences at a distance from the active volcanic zone (Amur deposit); and (3) Riphean (?) platform cover (Andree-Yul??evsky group of occurrences). The objects considered differ in origin. The hydrothermal Pb-Zn ores of the Biksizak deposit and the Kolpakovsky occurrence are epigenetic with respect to the host rocks. They were formed in the Early Carboniferous and related to early collisional minor andesite and quartz diorite porphyry intrusions. The hydrothermal-sedimentary Amur massive sulfide Zn deposit of the Filizchai type was formed at the end of Middle Devonian. Zinc occurrences of the Andree-Yul??evsky group are probably products of regeneration of older stratiform lodes.  相似文献   

8.
Results of the study of noble metal specialization of Lower and Middle Riphean terrigenous rocks in the Bashkir Anticlinorium (South Urals) are reported. The study revealed their genetic differences in the relatively unaltered, i.e., “background” terrigenous rocks in type sections of the Burzyan and Yurmatau groups and in sedimentary rocks of the same stratigraphic levels from tectonic zones subjected to local dynamothermal metamorphism of the greenschist facies and intruded by mafic rocks. It has been established that Ru serves as a geochemical marker of the impact of magmatic processes on sedimentary rocks and the redistribution of noble metals during metamorphism and local metasomatism. A generalized model is proposed for the formation of noble metal geochemical specialization of Lower and Middle Riphean terrigenous rocks in the South Urals.  相似文献   

9.
The Kyrpy Group of the East European platform is regarded by tradition as correlative with the Lower Riphean Burzyan Group of the Bashkirian meganticlinorium in the southern Urals. Age and correlation of the Kyrpy Group remain problematic, however, because of a limited geochronological information and controversial interpretation of paleontological materials. Data of C-and Sr-isotope chemostratigraphy contribute much to the problem solution. In the Kyrpy Group of the Kama-Belaya aulacogen, the Kaltasy Formation carbonates 1300 to 2400 m thick (boreholes 133 and 203 of the Azino-Pal’nikovo and Bedryazh areas) show 87Sr/86Sr ratios ranging around 0.7040 and narrow diapasons of δ13C values: about 0.5‰ (V-PDB) in shallow-water facies and-2.0‰ (V-PDB) in sediments of deeper origin. Despite the facies dependence of carbon isotope composition, δ13C variations not greater than ±1.0‰ are depicted in chemostratigraphic profiles of carbonate rocks characterizing separate stratigraphic intervals up to 800 m thick in the above borehole sections. Low 87Sr/86Sr ratios and almost invariant δ13C values in carbonates of the Kaltasy Formation are obviously contrasting with these parameters in the Middle and Upper Riphean deposits, being comparable with isotopic characteristics of the Lower Riphean sediments (Mesoproterozoic deposits older than 1300 Ma). Consequently, the results obtained evidence in favor of the Early Riphean age of the Kaltasy Formation and the Kyrpy Group as a whole.  相似文献   

10.
Based on the LA-ICP-MS data, detrital zircons from the tillite-type conglomerates of the Tanin Formation (Serebryanka Group) on the western slope of the Central Urals include approximately equal proportions of crystals with Neoarchean and Paleoproterozoic U-Pb ages. Therefore, we can assume that crystalline rocks of the basement beneath the eastern part of the East European Craton served as a provenance for aluminosilicate clastics in the initial Serebryanka period. Detrital zircons from sandstones of the Kernos Formation have the Meso-Neoarchean (∼15%), Paleoproterozoic (∼60%), and Mesoproterozoic (∼26%) age. Comparison of the obtained data with the results of the study of detrital zircons from Riphean and Vendian sandstones of the Southern Urals shows that the Riphean and Lower Vendian rocks are mainly represented by erosional products of Middle and Upper Paleoproterozoic crystalline rocks that constitute the basement of the East European Craton. In addition, a notable role belonged to older (Lower Proterozoic, Neoarchean and Mesoarchean) rock associations during the formation of the Serebryanka Group. The terminal Serebryanka time (Kernos Age) differed from its initial stage (Tanin Age) by the appearance of Mesoproterozoic complexes in provenances. According to available data, these complexes played an insignificant role in the formation of Riphean-Vendian rocks in the neighboring South Uralian segment. This implies a spatiotemporal diversity of clastic material sources for Upper Precambrian rocks in the western megazone of the Southern and Central Urals.  相似文献   

11.
The new version of the geological structure of the Berdyaush pluton (a single intrusion of rapakivi granites in the Urals) presented in this paper is significantly distinct from the previous structural schemes. Rapakivi granites compose no more than 10–20% of the area of the pluton and they are widespread only in its northeastern and southwestern flanks. The contacts between gabbro (I phase), hybrid syenodiorites (II phase), and rapakivi granites (III phase) are transitional, metasomatic. The hybrid syenodiorites and rapakivi granites are formed after gabbroic rocks as a result of their intense thermal and metasomatic transformation by the deep fluids. The driving force of this process could be the unilateral compression of the Berdyaush pluton resulting from formation of the eastward continental rift in the beginning of the Middle Riphean.  相似文献   

12.
The results of U/Pb dating of detrital zircons from sandstones of the Zigalga Formation, which is the base level of the Middle Yurmatu Group of the Bashkir uplift, southwestern Urals, are presented. The U/Pb ages of detrital zircons from sandstones of the Lower, Middle, and Upper Riphean are compared.  相似文献   

13.
The paper presents materials on a new (unconventional for the Urals) noble metal (platinum-gold-iron oxide) mineralization confined to terrigenous sequences of the Middle Riphean Mashak Formation on the western slope of the southern Urals. The mineralization is related to the percolation of reduced mantle fluids into upper levels of the crust at early stages of riftogenesis, their inversion in the crust, and redeposition of oreforming elements.  相似文献   

14.
The Rb–Sr and K–Ar characteristics of whole-rock argillite samples from the Middle Riphean Yurmatinian Group have been studied. The timing of final rock alteration was estimated at 525 ± 30 Ma by the Rb–Sr geochronometer. In the section near the Bol'shoi Avzhyan Settlement, the rocks experienced alteration up to the stage of deep epigenesis. The K–Ar data indicate that rock alterations continued after the Rb–Sr system conservation and was accompanied by a gradual gain of K. The great temporal gap between alterations of Middle and Lower Riphean rocks was established in the southern Urals. This gap may be explained either by the affiliation of sampled rocks to different tectonic units or by principal errors in stratigraphic correlations.  相似文献   

15.
New data are discussed on the distribution of mercury in the host volcanosedimentary and igneous rocks, hydrothermal—metasomatic rocks, and all types of modern newly formed materials (hydrothermal clays, argillized soil—pyroclastic beds, siliceous and limonite—hematite covers, bottom sediments, salt ‘sweat-outs’ of various compositions, etc.) typical of the supergene zone of geothermal deposits. By the example of the Nizhne-Koshelevskii (vapor-dominated) and Pauzhetka (water-type) geothermal deposits and thermal fields of the Koshelevskii volcanic massif and Kambal’nyi volcanic range (southern Kamchatka), the role of mercury was illustrated as an indicator element of the temperature, phase state, and dynamics of hydrothermal systems; intensity of rock argillization; and relative age (maturity) of geothermal deposits and thermal anomalies.  相似文献   

16.
We consider the general and specific features of the evolution of the composition of fine-grained terrigenous rocks in the Riphean sedimentary megasequences of the Southern Urals, Uchur-Maya region, and Yenisei Ridge. It has been established that the crust on the southwestern (in the modern frame of references) periphery of the Siberian craton was geochemically the most mature segment of the Riphean continental crust. For example, the fine-grained clastic rocks and metapelites of all Riphean lithostratigraphic units of the Yenisei Ridge have higher median contents of Th than the most mature Paleoproterozoic crust, and in median contents of Y and Cr/Th values they are the most similar to it. In the Southern Urals and Uchur-Maya region, some units of the Riphean sedimentary sequences show median contents of Y and Th and Cr/Th values close to those of primitive Archean crust. Analysis of Cr/Th variations in the fine-grained terrigenous rocks of all three megasequences shows that the minimum Cr/Th values, evidencing a predominance or the abundance of felsic rocks in provenances, are typical of the Riphean argillaceous shales and metapelites of the Yenisei Ridge. The distinct Cr/Th and Cr/Sc increase in the fine-grained clastic rocks of the Chingasan Group of the ridge reflects the large-scale destruction of continental crust during the formation of rift troughs as a result of the Rodinia breakup in the second half of the Late Riphean. The Cr/Th variations in the Lower and Middle Riphean argillaceous shales and mudstones of the Bashkirian mega-anticlinorium and Uchur-Maya region are in agreement, which evidences the subglobal occurrence of rifting in the early Middle Riphean (so-called “Mashak rifting”).  相似文献   

17.
Before our studies, it was considered that the Bagrusha rhyolite–porphyry complex (BC) including veins and thin dykes occurring in the Kusa region among deposits presumably of the Satka and Avzyan Formations of the Lower and Middle Riphean, respectively. Based on the U–Pb SHRIMP and IDTIMS studies of zircons from rhyodacite—porphyry, we established the age of the BC formation of T0 = 1348.6 ± 3.2 Ma for the first time. The age obtained is inconsistent with the idea on the Paleozoic age of the BC and the geological situation shown on geological maps of the region. The age (T0 = 1348.6 ± 3.2 Ma) of rhyodacite–porphyry from the BC provides evidence for acid volcanism controlled by the Mashak (Middle Riphean) magmatic event in the region, and deposits hosting volcanic rocks of the BC cannot be younger than the base of the Middle Riphean, i.e., the Mashak Formation, which was not previously distinguished by researchers in the western part of the Kusa and Bakal–Satka regions. At the same time, it is possible that deposits hosting dykes and veins of the granite–rhyolite formation may have a Bakal (Lower Riphean) age.  相似文献   

18.
Riphean stromatolitic formations flank the East European epi-Karelian platform only in the east and northeast. They are traceable as long (over 3600 km) relatively narrow belt consisting of two rectilinear segments, one running along the Urals western flank from southern extremity of the Bashkirian meganticlinorium to the Polyudov Ridge and the other one extending from the southern and central Timan to the Kil’din Island and northern Norway. Within the belt there are known stromatolitic formations of all Riphean erathems: the Lower and Middle Riphean stromatolitic buildups are confined to the eastern segment of its southern part only, while the Upper Riphean occur everywhere. Their distribution conformable to large structural elements of the plaform margin being replaced by carbonate-terrigenous rocks almost lacking stromatolites westward and southwestward in the Kama-Belaya aulacogen system and by substantially siliciclastic succession eastward and northeastward. The distribution area of Upper Riphean stromatolitic formations includes the Karatavian stratotype region, where 12 stromatolite beds ranging in age from ≥900 to 620 Ma are established. Many of the beds are traceable along the strike far beyond the stratotype region. Representing relatively small reference units, the beds facilitate reconstruction of distribution dynamics of the Upper Riphean stromatolites. Distribution area of the latter was always parallel to marginal structures of the platform, though being of changeable size, particularly of length. Originated in the stratotype region eastern part, stromatolites first advanced into northeastern areas never crossing boundaries of the Upper Riphean distribution area during the Early Karatavian. In the initial Late Karatavian, they occupied a longest distribution area that was sharply reduced at the end of that period. According to distribution peculiarities in space and with time, the Upper Riphean stromatolitic formations accumulated likely in peripheral areas of an open sea or oceanic basin adjacent to the East European platform, rather than in closed epiplatform basins.  相似文献   

19.
根据岩心及薄片观察,按照矿物晶体的大小、形状以及自形程度的差异,将塔里木盆地中央隆起中部中下奥陶统碳酸盐岩地层中的白云石分为6种类型,包括泥微晶白云石、粉—细晶自形—半自形漂浮状白云石、粉—细晶半自行—他形白云石、粉—细晶自形(环带)白云石、细—粗晶他形白云石、粗晶鞍形白云石。综合不同类型白云石的结构特征、碳氧锶同位素值、阴极发光等特征,认为中下奥陶统白云石主要由三种成岩作用形成:泥微晶白云石主要是在准同生期由回流白云石化形成;大部分粉—粗晶白云石是在埋藏期由埋藏白云石化形成,其中浅埋藏期是大规模白云石化的阶段;粗晶鞍形白云石主要由与高温热液活动相关的热液白云石化形成。  相似文献   

20.
经野外调研和室内研究,对老挝华潘省香科菱镁矿的矿区地质、矿体、围岩与夹石、矿石特征和矿床成因取得了一些新的认识。该矿区出露地层为下古生界（Pz1）、中-上石炭统（C2-3）和第四系河流二级阶地沉积（QpⅡal）,主要构造为1条北西向逆断层和4条北东向平移断层。矿体产于逆断层南西侧的强烈构造变形带中,呈脉状产出,厚度为数mm至10余cm,共圈出10个矿体。矿体的围岩与夹石的岩石类型相同,为浅变质陆源碎屑岩,具高硅（w（SiO2）为81.190%）、低镁（w（MgO）为0.781%）、富铁（w（Fe2O3）为11.716%、w（FeO）为1.719%）特征。矿石矿物为菱镁矿,脉石矿物主要为石英、金云母、白云石、绢云母和褐铁矿。香科菱镁矿的形成过程是：在中-晚三叠世的古特提斯洋封闭过程中,镁质从超镁铁岩中析出形成含矿热液,含矿热液迁移与富集后在强烈构造变形带中形成网脉状菱镁矿。香科菱镁矿的成因类型属产于浅变质碎屑岩中之老挝香科式晶质菱镁矿热液型矿床,成矿时代属中-晚三叠世。  相似文献   

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