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1.
邓敏  程锦翔  唐勇  付国斌  王正和  冯伟明  李嵘 《地质论评》2024,70(2):2024020016-2024020016
准噶尔盆地东部石钱滩凹陷石炭系巴塔玛依内山组火山岩之后发育一套连续稳定的碎屑岩沉积。笔者等通过XRD、主微量元素分析等手段针对其中的细粒沉积岩开展元素地球化学研究,其结果对恢复准东地区晚石炭世源区风化特征、古气候、判断其源岩性质及源区构造背景具有重要意义。研究表明,巴山组—石钱滩组泥岩具有低石英含量特点,其中巴山组泥岩黏土含量稍高,而石钱滩组泥岩中长石含量高,两者黏土成份均为蒙脱石（>99%）,反映了干燥、寒冷的气候特征且沉积介质长期为碱性;CIA结果显示巴山组—石钱滩组时期经历了中等—弱化学风化作用,并具有干湿交替气候变化特征;主微量元素及相关判别图解显示巴山组—石钱滩组泥岩的源岩多以偏中性的长英质火山岩为主,少量中基性及少量偏酸性的火山岩物源,并且多数为未分异的弧;泥岩的地球化学特征反映了沉积物源区构造背景主要为大陆岛弧背景,结合石钱滩组碎屑锆石峰值年龄及主要物源区分析认为,野马泉地体与其南部的准噶尔地体东北缘于335 Ma左右开始由俯冲转变为碰撞造山。  相似文献   

2.
Lithogeochemical features of Riphean fine-grained terrigenous rocks of the Kama-Belaya aulacogen are discussed. It is shown that aluminosiliciclastic material delivered to the aulacogen during the Riphean was characterized by a low maturity degree. The successively increasing K2O/Al2O3 values in the Riphean summary section correlate negatively with the CIA index values, indicating a gradually strengthening tendency for climate aridization in erosion zones. Data on some indicator ratios of trace elements and REE systematics in Riphean silty mudstones and shales of the Kama-Belaya aulacogen imply the involvement of mafic and ultramafic rocks, in addition to acid igneous and metamorphic varieties, in erosion during accumulation of the Nadezhdino, Tukaevo, Ol’khovka, Usinsk, and Priyutovo formations. Comparison of data on the composition of rocks in provenances based on the mineralogical-petrographic study of sandstones and investigation of geochemical features of silty mudstones and shales revealed their sufficiently high similarity. The geochemical data made it possible to specify the composition of rocks in provenances. Low Ce/Cr values in the fine-grained terrigenous rocks of the Lower Riphean Kyrpy Group suggest their formation with a significant contribution of erosion products of the Archean substrate, which is atypical for higher levels of the section. Thus, the Early-Middle Riphean transition period was likely marked by substantial changes in the mineral composition of material delivered to the Kama-Belaya aulacogen. The lack of exhalative components in the examined specimens of silty mudstones and shales points to a relatively low permeability of the Earth’s crust in the eastern East European Platform through the entire Riphean.  相似文献   

3.
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   

4.
Analysis of the litho-geochemistry of fine-grained terrigenous rocks (metapelites, shales, and mudstones) of sedimentary megasequences in the Southern Urals, Uchur-Maya area, and the Yenisei Kryazh indicates that Riphean sequences in these regions are dominated by chlorite-hydromica rocks, with montmorillonite and potassic feldspar possibly occurring only in some of the lithostratigraphic units. According to the values of their hydrolysate modulus, most clay rocks from the three Riphean metamorphosed sedimentary sequences are normal or supersialites, with hydrosialites and hydrolysates playing subordinate roles. The most lithochemicaly mature rocks are Riphean clays in the Yenisei Kryazh (Yenisei Range). The median value of their CIA is 72, whereas this index is 70 for fine-grained aluminosilicate rocks from the Uchur-Maya area and 66 for fine-grained terrigenous rocks of the Riphean stratotype. Hence, at ancient water provenance areas from which aluminosilicate clastic material was transported in sedimentation basins in the southwestern (in modern coordinates) periphery of the Siberian Platform, the climate throughout the whole Riphean was predominantly humid. At the same time, the climate at the eastern part of the East European Platform was semiarid-semihumid. The K2O/Al2O3 ratio, which is employed as an indicator of the presence of petro-and lithogenic aluminosilicate clastic component in Riphean sedimentary megasequences, shows various tendencies. According to their Sc, Cr, Ni, Th, and La concentrations and the Th/Sc ratio, the overwhelming majority of Riphean shales and mudstones notably differ from the average Archean mudstone and approach the average values for post-Archean shales. This suggests that mafic Archean rock in the provenance areas did not play any significant role in the origin of Riphean sedimentary megasequences. The Co/Hf and Ce/Cr ratios of the terrigenous rocks of the three Riphean megaseqeunces and their (Gd/Yb) N and Eu/Eu* ratios place these rocks among those containing little (if any) erosion products of primitive Archean rocks. According to various geochemical data, the source of the great majority of fine-grained aluminosilicate clastic rocks in Riphean sediment megasequences in our study areas should have been mature sialic (felsic), with much lower contents of mafic and intermediate rocks as a source of the clastic material. The REE patterns of the Riphean shales and metapelites in the Bashkir Meganticlinorium, Uchur-Maya area, and Yenisei Kryazh show some features that can be regarded as resulting from the presence of mafic material in the ancient provenance areas. This is most clearly seen in the sedimentary sequences of the Uchur-Maya area, where the decrease in the (La/Yb) N ratio up the sequence of the fine-grained terrigenous rocks from 15–16.5 to 5.8–7.1 suggests that mantle mafic volcanics were brought to the upper crust in the earliest Late Riphean in relation to rifting. Analysis of the Sm-Nd systematics of the Riphean fine-grained rocks reveals the predominance of model age values in the range of 2.5–1.7 Ga, which can be interpreted as evidence that the rocks were formed of predominantly Early Proterozoic source material. At the same time, with regard for the significant role of recycling in the genesis of the upper continental crust, it seems to be quite possible that the ancient provenance areas contained Archean complexes strongly recycled in the Early Proterozoic and sediments formed of their material. An additional likely source of material in the Riphean was mafic rocks, whose variable contribution is reflected in a decrease in the model age values. Higher Th and U concentrations in the Riphean rocks of the Yenisei Kryazh compared to those in PAAS indicate that the sources of their material were notably more mature than the sources of fine-grained aluminosilicate clastic material for the sedimentary megaseqeunces in the Southern Urals and Uchur-Maya area.  相似文献   

5.
贵州岩溶区红色风化壳是中国南方红色负化壳的重要组成部分，本文根据部分红色风化壳剖面野外特征、矿物学、地球化学及土壤物理学等的研究结果，对其物源及成因进行了探讨。各剖面，尤其邻近剖面显著的矿物学、地球化学差异排除了远程风成沉积物、火山灰、上覆或者高处碎屑岩层作为统一且重要物源的可能。极低的石英含量表明贵州常见的长石石英砂岩不是其主要物源，具有中稀土（MREE）富集的特征也排除了粘土岩、页岩作为主要物源的可能。风化壳剖面间的差异性均可从基岩酸不溶物的差异性得到很好解释，表明它们是下伏碳酸盐岩风化、酸不溶物（准）原地堆积的结果。部分剖面甚至显示了典型风化壳剖面的一些特征，具有正常风化序列的剖面结构特征。  相似文献   

6.
Mineralogical and chemical investigations (<2μm clay separates) of shale samples from the Neogene-age Surma Group obtained from four wells (Habiganj-11, Shahbazpur-1, Titas-11, Titas-15) in the Bengal basin, Bangladesh, were carried out in order to reveal the clay mineral composition as reservoir exploration and exploitation requires a good understanding of the clay minerals. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-Ray fluorescence spectrometry (XRF). Mineralogically, the sub-surface Surma Group shales comprise predominantly quartz, plagioclase, illite, chlorite, kaolinite, with lesser amounts of K-feldspar, dolomite and smectite, and minor to trace amounts of calcite, siderite and pyrite. The chemical composition of the <2 μm clay separates also suggests an illite and chlorite-rich composition. With increasing burial depth, the Surma Group shales are enriched in illite. The gradual decreasing of the smectite clays with depth and ultimate disappearance at greater depths (≥ 3000 m) may have been responsible for the presence of the diagenetic illite. Based on the mineralogical composition it is most likely that the illite-chlorite associations together with quartz and feldspar were predominantly detrital in origin and thus reflect the presence of a rapidly-rising source terrain not subjected to intense weathering.  相似文献   

7.
The Sardar Formation (Carboniferous) has a lithological variation that is characterized by sandstone, shale and limestone members. Shales of the Sardar Formation from the east central Iran have been analyzed for major elements and a number of trace elements. The shales of Sardar Formation are rich in quartz minerals and clay minerals of the bulk minerals. Clay minerals of shales are composed of illite, kaolinite and slightly montmorillonite. SiO2 versus K2O/Na2O diagram shows these shales plotted in the passive continental margin or cratonic field. Geochemical data suggest high acidic source rocks similar to granite and intermediate igneous rocks. CIA and ICV suggest semi-humid climatic conditions during depositions and indicate high chemical weathering in the source area. The geochemical parameters such as V/Cr, Ni/Co and Cu/Zn ratios indicate that these shales were deposited in oxic environment.  相似文献   

8.
东营凹陷永北地区T1不整合面之下风化壳发育带的的预测是地层油藏勘探的重点与难点。综合利用高精度三维地震解释、岩心观察、薄片鉴定、测录井分析及物性分析等方法,结合构造发育史、埋藏史等研究成果,对东营凹陷永北地区T1不整合面下沙三上亚段地层中特殊的地震反射特征进行研究,并对其地质意义进行了探讨。研究表明:T1不整合面下发育典型埋藏风化壳,包括风化粘土层和半风化淋滤带2层结构;在大气淡水风化、淋滤作用下,半风化淋滤带内部地震同相轴消失,表现为空白反射特征;半风化淋滤带物性得到改善,与未风化岩石之间形成一个物性差异界面,表现为不连续的角度不整合面;未受明显风化、淋滤作用的地层,则表现为典型的角度不整合;地震反射特征的演化过程可划分4个阶段:沙三上沉积后阶段、沙三上抬升后阶段、风化壳形成早期阶段、风化壳形成阶段。地震空白反射带的发育范围是风化壳发育带的保守范围或最小范围,向湖盆方向逐渐过渡为正常地层。风化壳的发育大大改善了原岩的储集性能,可作为良好的油气储集空间和运移通道,是下步地层油气藏勘探的重点目标。  相似文献   

9.
峨眉山大火成岩省在形成后遭受了强烈的风化剥蚀，与右江盆地构成了独特的源- 汇沉积体系，相关的碎屑沉积记录是重建峨眉山大火成岩省晚期火山序列、揭示大火成岩省岩浆演化的关键。本文对黔西南地区右江盆地北缘下三叠统下部飞仙关组开展了详细的沉积物源研究。飞仙关组泥岩由长石、石英和黏矿物等组成，具有低SiO2、高TiO2含量和低Al2O3/TiO2值的特征，具Eu的弱负异常，微弱的Nb、Ta负异常。基于Al2O3/TiO2和La/Sm物源图解分析，研究样品的主要物源由峨眉山大火成岩省的高- Ti玄武岩和少量酸性火山岩构成，这与右江盆地晚二叠世的碎屑沉积物源组成一致。碎屑锆石具有～260 Ma 的年龄峰值，对应锆石具有较低的Th/Nb和较高的Nb/Hf值，均支持峨眉山大火成岩省作为主要的沉积物源区，而同时存在的>400 Ma的碎屑锆石则对应于峨眉山玄武质岩浆上升时所捕获的华南地壳物质。与上二叠统的碎屑锆石U- Pb年龄组成和锆石化学组成对比分析表明，峨眉山大火成岩省在晚二叠世到早三叠世早期剥蚀的火山岩构成了一定的火山序列，反映了该大火成岩省晚期从强烈地壳混染到分异结晶为主的岩浆演化过程。  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 Grenvillian orogeny (～1250 to 980 Ma) was one of the most significant Riphean events. It determined the formation of many structures observable now in North and South America, northwestern Europe, South Africa, Western Australia, Antarctica, and other regions. Nevertheless, its reflections in the most complete and relatively well investigated Upper Precambrian sedimentary sections of northern Eurasia such as the Riphean stratotype (Bashkir meganticlinorium) and hypostratotype (Uchur-Maya region) still remain unknown. This is primarily true of the petrographic and chemical compositions of terrigenous rocks. This work is dedicated to the analysis of peculiar features in variations of the whole-rock chemical composition of sandstones and fine-grained clastic rocks (shales, mudstones, fine-grained clayey siltstones) that constitute Middle-Upper Riphean boundary layers of the Bashkir meganticlinorium, Kama-Belaya aulacogen, and Uchur-Maya region. The analysis reveals no tendency for the decrease in the degree of the chemical and, consequently, mineralogical maturity in the upward direction through the Middle-Upper Riphean sections in the above-mentioned regions. The whole-rock compositions of fine-grained clastic rocks associated with sandstones correspond mostly to that of “common” Upper Precambrian clayey rocks. The formation of practically the entire Yurmatinian-Karatavian succession in the Bashkir meganticlinorium proceeded under relatively stable TDM and ?Nd(T) values. The period of 1250 to 980 Ma in the central and eastern parts of the Siberian Platform was marked by repeated rifting episodes alternating with accumulation of mature platformal sediments, although repercussions of Grenvillian collisional processes are missing from this region as well. The performed analysis provides grounds for the conclusion that contribution of the Grenvillian events to the formation of most complete Riphean successions in northern Eurasia was insignificant.  相似文献   

12.
岩石的组分、结构和颗粒排列,决定了孔隙的发育特征,但从结构-成因角度探讨碎屑颗粒含量及其排列样式对泥页岩孔隙分布影响的研究较少。以黔西北志留系龙马溪组黑色泥页岩为例,基于薄片分析、XRD分析和扫描电镜等分析结果,根据碎屑颗粒排列方式,将泥页岩分为“颗粒分散状”和“纹层状”两种类型,提出泥页岩孔隙结构的概念模型,由此分析碎屑颗粒含量对孔隙发育的影响。对于“颗粒分散状”泥页岩来讲,碎屑颗粒含量低于52.4%时,主要发育黏土矿物微孔隙,孔隙度随颗粒含量的增加而减小;当碎屑颗粒含量达到52.4%时,颗粒间全部为黏土矿物充填,孔隙度最低;当碎屑颗粒含量继续增加时,粒间孔隙大量出现,孔隙度也将迅速增大。对于“纹层状”泥页岩,颗粒含量的增加会导致砂质纹层内的粒间孔隙不断增多,孔隙度也随之增大,逐渐向常规的碎屑岩储层转变。本模型有助于加深对泥页岩、致密砂岩和常规砂岩孔隙发育机理的理解,对非常规储层的预测评价也有重要启示。  相似文献   

13.
以"沉积控相,相控储层"为研究思路,基于野外露头剖面实测与室内实验测试,以及前人的研究成果,探讨渝东北地区上奥陶统五峰组-下志留统龙马溪组沉积环境对页岩气储层的控制作用。研究表明,渝东北地区五峰组-龙马溪组富有机质泥页岩主要发育于滞留浅海陆棚相中,沉积中心页岩厚度可达70~80m,有机碳含量(TOC)最高可达7.56%,平均3.09%。静水缺氧还原沉积环境岩石类型主要以富含有机质的含碳质含粉砂泥(页)岩、含碳质含硅质泥(页)岩、含硅质泥(页)岩、含碳质泥(页)岩、含粉砂泥(页)岩及硅质泥(页)岩为主。页岩矿物成分以石英(平均达62.76%)和黏土矿物(平均达22.61%)为主。缺氧还原环境下沉积的大量黄铁矿形成的黄铁矿晶间孔、黏土矿物层间微孔隙、有机质生烃形成的微孔隙以及脆性矿物控制形成的微裂缝为页岩气提供了良好的储集空间。沉积环境控制的储层发育特征的研究可为页岩展布、有机质丰度、储集空间及其之后有利区评价等研究提供基础。  相似文献   

14.
孙林华  桂和荣 《地球学报》2011,32(5):523-532
在对安徽省北部宿州新元古代史家组砂岩地球化学特征分析的基础上,结合前人发表的淮南和凤阳新元古代刘老碑组页岩的地球化学数据,对它们的物源和构造背景进行了对比讨论.结果表明:刘老碑组页岩的地球化学特征表明其来自于中-酸性火成岩高程度的首次风化,而史家组砂岩则来自于经历了再循环的古老地壳物质较低程度的风化.刘老碑组页岩相对史...  相似文献   

15.
We report the results of geochemical, Sm–Nd isotope–geochemical, and U–Pb detrital zircon geochronological studies of metaterrigenous rocks of the Glubokin Formation assigned provisionally to the Upper Riphean. This formation is developed where the Mongol–Okhotsk belt is almost completely squeezed by the surrounding continental structures and, hence, bears important information on its evolution. The obtained results suggest the following conclusions: (1) the Glubokin Formation is Early Pennsylvanian or post-Early Pennsylvanian in age, not Riphean as previously suggested; (2) the Glubokin Formation belongs to the Mongol–Okhotsk Fold Belt rather than to the Argun continental massif, as suggested in the existing schemes of structural zoning; (3) the volcanogenic-terrigenous deposits of the Glubokin Formation were precipitated in a back-arc basin setting above the subduction zone subsiding beneath the southeastern margin of the North Asian Craton; and (4) the main sources of clastic material for the Glubokin Formation were igneous and metamorphic complexes of different ages from the southeastern margin of the North Asian Craton.  相似文献   

16.
<正>Red clay type gold deposits,located in the south of China,are situated not only in orogenic belts,but also in inner cratons,where climate is tropical-subtropical with clear arid and humid.The lateritic weathering crust often can be divided into five zones,including topsoil,siliceous duricrust zone,multi-color zone(or red clay zone in some deposits),pallid zone and saprolite zone from surface to the base rock,several of which are absent in some deposits.The base rocks are composed mainly of carbonate rocks with minor clastic rocks,intermediate-basic volcanic rocks and intermediate-acid and alkalic intrusions.The orebodies are mainly located in the multi-color zone with part of them in the pallid and saprolite zones.The ore sources include orebodies of Carlin-type gold deposits and porphyry gold deposits,as well as gold-rich base rocks.The red clay type gold deposits experienced early-stage endogenic gold mineralization and laterization during the Tertiary and Quaternary.The areas with endogenic gold deposits,especially Carlin-type gold deposits and porphyry gold deposits in karst depressions on the plateau,structual erosional platforms in the middle-lower mountains,and intermountain basins in southern China are well worth studying to trace red clay type gold deposits.  相似文献   

17.
南翼山构造地表狮子沟组发育混积岩,作为一种特殊类型的沉积岩,其研究具有一定的实际意义和科学价值。本文在野外观察和镜下鉴定的基础上,对南翼山混积岩样品进行了X衍射、主微量元素及碳氧同位素测试,分析了混积岩的岩石学特征,考虑到其成分和成因的复杂性,通过数据分析排除了多种干扰因素,最后利用有效指标综合判断了其沉积环境。结果显示：南翼山构造地表混积岩中陆源碎屑平均含量为58.7%,碳酸盐矿物含量为31.0%,属于碳酸盐质陆源碎屑岩,主要为钙质泥岩,其中碎屑矿物以细粉砂级石英为主,碳酸盐矿物主要为泥晶方解石,黏土矿物组合为伊利石和有序伊蒙混层,且三者呈均匀混合的特征。数据分析表明Ca、Na、Mn、Sr、Ba等元素主要来源于自生矿物,稀土元素及碳氧同位素组成未受成岩作用影响,可以作为判断沉积时水体盐度和氧化还原条件的指标。根据Sr/Cu比值和K2 O/Al 2O3比值,结合黏土矿物组合及伊利石结晶度和化学指数,判断地表混积岩沉积时为寒冷干旱的气候条件;Sr/Ba比值和Z值表明古水体介质为咸水环境;U/Th比值、自生U含量和Ce轻微负异常等指标综合判定其形成于弱氧化环境。以上研究表明,南翼山构造地表混积岩主要为陆源碎屑和碳酸盐矿物均匀混合的钙质泥岩,形成于寒冷干旱气候条件下的弱氧化咸水湖泊环境中。  相似文献   

18.
The comprehensive study of sections of the Shatak Complex has revealed that conglomerates at the base of Middle Riphean rocks are not basal but intraformational rocks. Previously described angular unconformities between shales of the Sukhin Subformation (Yusha Formation, R1) and conglomerates of the Kuz”elga Subformation (Mashak Formation, R2) are related to late tectonic movements. Magmatic rocks developed at the base of the Middle Riphean section are represented by sheet intrusions formed in the course of emplacement of a fluid-saturated magmatic melt into partially or completely lithified terrigenous rocks at the graben formation stage during the origination of synkinematic faults that served as magma conduits. It is inferred that distribution of provenances of clastic materials and sedimentation basins in the Burzyanian and Yurmatian should be scrutinized in the study region, because the normal regressive sequence of rocks from the uppermost Yusha Formation to the lowermost Mashak Formation, which was established in the Shatak Ridge, eliminates a clear boundary distinguished between them at present. The idea about an older age of the Mashak conglomerates is substantiated.  相似文献   

19.
The clarkes of concentrations (Kc) of a wide range of trace elements (Li, Be, B, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, In, Sb, Cs, Ba, REE, Hf, Ta, Hg, Tl, Pb, Bi, Th, and U) were analyzed for fine-gained terrigenous rocks (mudstones, metapelites) from the reference Riphean sections of the Uchur-Maya region and the Yenisei Range. It was established that the shales and mudstones of the Uchur and Aimchan groups in the Riphean hypostratotype section are characterized by moderate (2.5 < Kc < 5) and intense (Kc > 5) geochemical specialization for Li, B, and Zn. At the same time, the similar rocks of the Lakhanda and Ui groups do not exhibit any distinct geochemical specialization, although they are notably enriched in HREE. The metapelites from the basal formations of the Riphean sedimentary successions in the Yenisei Range are distinctly specialized for B and slightly for Li, Rb, Be, Nb, Ta, Th, Ge, and Cd. In addition, moderate specialization for Cu is characteristic of the metapelites from the Korda and Lopatino formations; for Bi, Sb, Hg, and V, for their analogs from the Potoskui Formation; and, for Hg and Cs, for the similar rocks from the Lopatino Formation. The metapelites of the Lower Riphean Korda Formation from the central zone of the Yenisei Range have elevated contents of significantly more elements (Li, Be, Sc, V, Cr, Co, Ni, Zn, As, Rb, Y, Zr, Nb, Sb, Ag, In, Hf, Hg, and others) than their counterparts from its eastern near-platform part. The mudstones of the ore-bearing (Pb, Zn) Gorevo Formation are characterized by elevated concentrations of several ore elements such as Pb, Cd, As, Sb, and Bi. The elevated Kc values of the rare lithophile and of several ore elements in the metapelites of the Yenisei Range are determined by the high geochemical differentiation of the Early Precambrian blocks constituting the western margin of the Siberian Craton, which were eroded in the Riphean, and the syn-sedimentary riftogenic and intraplate magmatism. On the contrary, the fine-grained and terrigenous rocks from the basal part of the Riphean section in the Uchur-Maya region are compositionally closer to the immature Late Archean substrates or their Early Proterozoic analogs.  相似文献   

20.
Using an instrumental technique, we carried out a direct comparison of quartz from the Riphean sandstones, sandy fractions from fragments in the Riphean conglomerates and Archean crystalline rocks, which represent the basement inlier of the Russian Platform within the Western Urals (Taratash anticlinorium). It is shown that clastic quartz in the Riphean basal complexes was mainly related to denudation of the Lower Proterozoic platformal cover, whose rocks occur as fragments in the Riphean conglomerates. The probable contribution of eroded crystalline rocks into the Riphean sediments was presumably very insignificant.  相似文献   

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