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1.
The available data on the age and formation conditions of the granulite complexes in the western Dzhugdzhur-Stanovoi Fold Region (Dambuki and Larba blocks) and the adjacent territory of the Peristanovoi Belt (Kurul’ta, Zverevsky, and Sutam blocks) are systematized. At least three Early Precambrian episodes of high-grade granulite-facies metamorphism dated at 2.85–2.83, 2.65–2.60, and 1.90–1.88 Ga are established in the geological history of the western Dzhugdzhur-Stanovoi Fold Region. Five granulite-facies metamorphic events are documented in the Peristanovoi Belt. The early granulite-facies metamorphism, migmatization, and emplacement of charnockite are related to the first event (2183 ± 1 Ma) in the Kurul’ta Block. The structural transformation and metamorphism of charnockite under conditions of granulite facies correspond to the second event (2708 ± 7 Ma). The enderbite belonging to the Dzhelui Complex (2627 ± 16) and charnockite of the Altual Complex (2614 ± 7 Ma) were emplaced during the third tectonic event, which was immediately followed by the emplacement of the Kalar anorthosite-charnockite complex (2623 ± 23 Ma). The first episode of Early Proterozoic granulite-facies metamorphism of the Sutam Sequence in the tectonic block of the same name was related to the fourth event, probably caused by collision of the Olekma-Aldan continental microplate and the passive margin of the Uchur continental microplate. Finally, granulite-facies metamorphism superimposed on rocks of the Kalar Complex in the Kurul’ta Block and high-pressure metamorphism in the Zverevsky and Sutam blocks (1935 ± 35 Ma) correspond to the fifth metamorphic event. The Late Archean metamorphic events are most likely related to the amalgamation and subsequent collision of the terranes which currently make up the granulite basement of the Dzhugdzhur-Stanovoi Fold Region with the Olekma-Aldan continental microplate. In the Early Proterozoic, the Aldan Shield and the Dzhugdzhur-Stanovoi Fold Region were separated by an oceanic basin. Its closure, and the collision of the Aldan and Stanovoi continental microplates, were accompanied by granulite-facies metamorphism and led to the formation of the Peristanovoi Belt, or Peristanovoi Suture Zone. This collision suture continued functioning in the Phanerozoic (from the Early Jurassic to the Early Cretaceous) with the formation of thick shear zones and greenschist retrograde metamorphism.  相似文献   

2.
Two types of Precambrian high-grade metamorphism, Inner Mongolia, China   总被引：20，自引：0，他引：20  
Abstract Archaean and Proterozoic granulite facies complexes of Inner Mongolia differ in lithological association, tectonic style, mineral assemblage and metamorphic P–T path. A nearly isobaric cooling path for Archaean high-grade metamorphic rocks is suggested by reaction textures and geothermobarometry. Early Proterozoic metamorphic rocks show nearly isothermal decompression. Archaean metamorphism may have been caused by magmatic accretion, whereas early Proterozoic metamorphism suggests a major continental thickening event followed by exhumation.  相似文献   

3.
According to differences of the protolith formations, the early Precambrian strata in the northern part ofthe North China platform may be divided into the stable stratigraphic region in the west and the mobilestratigraphic region in the east. Based on unconformities, either stratiragphic or tectonic, as well as significantmetamorphic thermal events, the two regions may be stratigraphically defined as follows: 1) the middleArchaean Fuping Supergroup composed of the Chenzhuang and Wanzi Groups (stable areas), and the middleArchaean Qianxi Group (mobile area), whose upper limits are all dated at 2800 Ma; and 2) the upper ArchaeanWutai Supergroup composed of the Longquanguan, Shizui and Taihuai Groups (stable areas), and the upperArchaean Zunhua, Dantazi and Zhuzhangzi Groups (mobile areas). whose upper limits are all dated at 2500Ma. A correlation of the above-mentioned units is also made. The lower Proterozoic Hutuo Group of the sta-ble region is adjusted to comprise the Gaofan, Doucun, Dongye and Guojiazhai Groups. The upper limit of theGaofan Group is placed at 2350 Ma, Dongye 1850 Ma and Guojiazhai (the lower limit of the Changcheng Sys-tem) 1700 Ma.  相似文献   

4.
Regolith occurs at a number of localities along the northern margin of the early Proterozoic Pechenga Greenstone Belt marking a profound stratigraphic unconformity at the base of the 10 km thick Petsamo Supergroup. The age of regolith formation can be bracketed between 2.453 ± 42 Ga (Sm-Nd) and 2.330 ± 36 Ga (Rb-Sr). Regolith is developed on a varied substrate of Archaean rocks including early Proterozoic layered gabbros (2.45 Ga). The best example of the regolith occurs in the Pasvik valley at Brattli, Norway. Analogues are widespread on the Baltic Shield at the base of early Proterozoic 'greenstone belts' showing a low degree of chemical weathering and carbonatisation. Fluviatile deposits overlying the Brattli regolith preserve unweathered pyrite-magnetite boulders and terrigenous pyrite grains. These features are considered to relate an arid or semi-arid palaeoenvironment, possibly with some deficiency of oxygen in the atmosphere-hydrosphere system. A systematic and well-preserved regolith or palaeosaprolite at the base of the Petsamo Supergroup is proof that the northern boundary of the Pechenga Greenstone Belt is a fundamental first-order unconformity. This places constraints on geotectonic modelling of this early Proterozoic rift-basin.  相似文献   

5.
Based on traditional petrochemical and nontraditional mineralogical methods (accessory zircon generation analysis), specific features of the primary composition of strongly metamorphosed rocks from some Early Precambrian Au-bearing rocks of the Ukrainian Shield (US) were studied. The confinement of several gold ore occurrences to primarily sedimentary Late Archean rocks of the Ukrainian Shield has been established and the possibility of their chemogenic origin is considered. The joint analysis of plicative tectonics and metamorphism facies in the study area demonstrated that Au-bearing primarily sedimentary (chemogenic) rocks of the Khashchevatoe–Zaval'ev Formation of the Bug Group (AR2) are confined to amphibolite-facies domains within tectonic (high-order synform) structures with a significant gold potential.  相似文献   

6.
The first attempt at coordination of the newest geochronological findings with identifiable petrographic complexes within the Ukrainian Shield, here seen as products of geosynclinal evolution and of granitization (in the modern sense), suggests the following characteristic traits of the Precambrian evolution of the earth's crust: an arrest of the upper Archean geosynclinal cycle (the second one of the three) in its initial or early stages; a general non-inversion of geosyncline; a very high geothermal gradient and hence the cardinal role of granitization and the "universality" - involvement of practically all kinds of rocks - of the regional metamorphism. The Shield has behaved as a platfomal entity ever since the end of its last (lower Proterozoic) geosynclinal cycle. The author's historical analysis of the Shield, as distinct from the still current stratigraphic representations, is based among other things on the recognized independence of metamorphic facies from stratigraphic as well as structural boundaries, identifications of formations corresponding to definite stages and zones of the geosynclinal evolution, correlations of geochronological data with petrographic varieties of rocks and with their spatial distribution, examination of migmatites and granitoids from the viewpoints of ultrametamorphism and granitization, proofs of the function of deep fissuring in the character of sedimentation and intrusive activities, and plane analysis of folded structures. Metallogenic analysis of the Shield is facilitated by such identifications and correlations, inasmuch as migrations and accumulations of ore constituents and others were definitely associated with granitization activities. — V. P. Sokoloff  相似文献   

7.
本文基于大量文献资料,系统研究俄罗斯北极地区前寒武纪的岩相古地理。俄罗斯北极地区前寒武纪共识别出半深海-深海区、浅海区、滨海区、冲积区和隆起剥蚀区5种古地理单元,其中,隆起剥蚀区沉积记录缺失;冲积区以砾岩+砂岩+泥岩和变质碎屑岩+碳酸盐岩为主;滨浅海区沉积则以变质碎屑岩+碳酸盐岩、蒸发岩+碳酸盐岩、砂岩+泥岩+碳酸盐岩3种岩性组合为主,局部有蒸发岩、砾岩+砂岩+泥岩发育;而半深海-深海区为大洋。俄罗斯北极地区前寒武纪古地理以滨浅海区为主,主要分布在东西伯利亚台地、西西伯利亚盆地、鄂霍茨克地块、楚科奇板块和巴伦支海北部地区;半深海-深海区的分布仅次于滨浅海区,此时西西伯利亚盆地尚未完全形成,其东侧为半深海-深海区;隆起剥蚀区分布范围小于半深海-深海区,主要分布在波罗的地盾及其周缘地区,以及东西伯利亚台地的阿纳巴尔地块和阿尔丹地盾地区;冲积区分布范围最为局限,仅在蒂曼-柏朝拉盆地中部发育。研究表明,俄罗斯北极地区广泛发育前寒武纪地层,岩性以碳酸盐岩和变质碎屑岩为主,部分构造单元中的前寒武纪地层已成为陆壳基底,前寒武纪岩相古地理特征研究可为前寒武纪地质研究提供依据,为其余地质时期的岩相古地理研究奠定基础。  相似文献   

8.
《International Geology Review》2012,54(10):1771-1783
Precambrian conglomerates, generally metamorphosed with concomitant loss of form, orientation, structure, and texture, are often regarded as fault breccias, mylonites, and even porphyroblastic formations. Study of the Precambrian of the Kola Peninsula has revealed that Proterozoic conglomerates are common, and although many original rock features have been obliterated by metamorphism, detailed study has led to the conclusion that valuable stratigraphic and petrologic data are discernible. The distribution of various metamorphosed conglomerates, their stratigraphic position and relationship to the enclosing rocks, their structure, the nature and location of source rocks, and the probable modes of transportation and environments of deposition were determined for many metamorphosed Proterozoic conglomerates of the eastern Kola Peninsula. This study shows that valuable information on the pre-metamorphic history of Precambrian areas can be obtained by careful analysis of metasedimentary rocks.—R. D. DeRudder  相似文献   

9.
As part of our ongoing research on the application of elemental geochemistry methods to Early Precambrian ferrous quartzite formations and in order to elucidate the nature of their ore material, we investigated the distribution of As, Sb, and Bi in exogenic oxide-hydroxide iron ores, sedimentary carbonate rocks and iron ores, and ferro-siliceous formations of the Krivoi Rog (Ukrainian shield), Kursk-Belgorod (Voronezh crystalline massif), Kostomuksha, and Imandra iron ore provinces (Baltic shield) of the Late Archean and Early Proterozoic. The results of the elemental geochemical investigations were used to evaluate the plausibility of some geological and geochemical models of Early Precambrian ferro-siliceous ore formation.  相似文献   

10.
Gas chromatography and other analytical techniques (EMR, PMR, and IR spectroscopy) were used to examine volatile components (CH4, C2-C3, CO2, CO, H2, H2O, and others) in alkaline rocks and minerals from the Ukrainian Shield (eight massifs and dikes of grorudites) and from the Khibina and Lovozero massifs in the Baltic Shield. The alkaline rocks from the Ukrainian Shield are mostly of Proterozoic (1.7–2.1 Ga) age. The alkaline rocks from the Kola Peninsula were confirmed to be rich in methane (21 ± 14 μl/g on average) and other hydrocarbons, whereas the analogous rocks from the Ukrainian Shield are poor in methane (2.1 ± 1.6 μl/g on average at a maximum of 14 μl/g). The latter rocks are richer in CO2, which is one of the major volatile components of alkaline rocks, including agpaitic nepheline syenites from the Kola Peninsula. The rocks from the Ukrainian Shield often have elevated contents of nitrogen (up to 20 μl/g). The reasons for the differences in the composition of volatile components of rocks from the Kola Peninsula and Ukrainian Shield are as follows: the agpaitic crystallization trends of large massifs in the Kola Peninsula and much less clearly pronounced agpaitic trends in the small massifs in the Ukrainian Shield, the affiliation of these rocks with different complexes, the deeper erosion levels of the Ukrainian alkaline massifs, different ages of these rocks, etc.  相似文献   

11.
The autonomous (massif-type) anorthosite massifs of the Kalar Complex (2623 ± 23 Ma) intrude high-grade metamorphic rocks of the Kurulta tectonic block at the junction of the Aldan and Dzhugdzhur-Stanovoi fold area. These rocks belong to the most ancient anorthosite-mangerite-charnockite-granite (AMCG) magmatic association, whose origin was constrained to the Mesoproterozoic (1.8–1.1 Ga). The charnockites are typical high-potassium reduced granites like rapakivi, which affiliate with the A type. The Nd and Pb isotopic composition of these rocks suggests their predominantly crustal genesis, whereas the anorthosites were most probably produced by a mantle magma that was significantly contaminated by crustal material at various depth levels. The intrusions of the Kalar Complex were emplaced in a postcollision environment, with the time gap between the collisional event and the emplacement of these massifs no longer than 30 m.y. The southern Siberian Platform includes two definitely distinguished and spatially separated AMCG associations, which have different ages and tectonic settings: (i) the Late Archean (2.62 Ga) postcollision Kalar plutonic complex and (ii) the Early Proterozoic (1.74–1.70 Ga) anorogenic Ulkan-Dzhugdzhur volcano-plutonic complex.  相似文献   

12.
峡河岩群是从原秦岭岩群中部新解体出的中元古代地层单位，分布于豫陕交界处，呈北西向展布。在晋宁期，峡河岩群原岩下冲深埋，形成变质地体；加里东—海西期韧性抬升改造并遭受花岗热穹叠加。这些过程伴随有榴辉岩的构造侵位及高压变质。  相似文献   

13.
The central portion of the Aldan Shield hosts very widely spread Archean and Early Proterozoic granitoids, much of which are granite-gneisses. Geochemical lines of evidence, data on inclusions in minerals, and Sm-Nd isotopic geochemical data suggest that the protoliths of granite-gneisses in the central part of the Aldan Shield were granitoids that had various composition, age, and were derived from distinct sources and under different parameters and were then emplaced in different geodynamic environments. The granitoids belong to at least two types of different composition that occur within spatially separated areas. The protoliths of granite-gneisses in the western part of the Western Aldan Megablock and the junction zone of the Chara-Olekma and Aldan geoblocks (granite-gneisses of type I) had the same age and affiliated to the same associations as the within-plate granitoids of the Nelyukinskii Complex. Their parental melts were derived at 2.4–2.5 Ga by the melting of Archean tonalite-trondhjemite orthogneisses of the Olekma and Aldan complexes. The protolith of granite-gneisses in the eastern portion of the Western Aldan Megablock (granite-gneisses of type II) can be subdivided into two groups according to their composition: granitoids with geochemical characteristics of subduction- and collision-related rocks. The protoliths of the type-II granite-gneisses with geochemical characteristics of subduction granitoids were produced simultaneously with the development of the Fedorovskaya island arc (at 2003–2013 Ma), whereas the protoliths of the type-II granite-gneisses with geochemical characteristics of collision granitoids were formed in the course of accretion of the Fedorovskaya island arc and the Olekma-Aldan continental microplate at 1962–2003 Ma, via the melting of magmatic rocks of the Fedorovskaya unit and older continental crustal material.  相似文献   

14.
Within the Caledonian complexes of northwestern Spitsbergen, high PT formations provide U---Pb zircon ages of 965±1 Ma of a metagranite and 955±1 Ma of a corona gabbro, indicating the influence of Grenvillian activity in the area. Various isotopic systems suggest that these rocks were partially derived by reworking of ancient crust (as old as Archaean). Eclogites and felsic agmatite indicate latest Proterozoic magmatic or metamorphic events (625−5+2 and 661±2 Ma, respectively) by U---Pb zircon dating. The eclogitic metamorphism age is not fully constrained and ranges between 540 and 620 Ma; this occurred prior to the superimposed Caledonian metamorphism, indicated by a part of the K---Ar and Rb---Sr mineral cooling ages. The new data and other evidence of Precambrian tectonothermal activity on Svalbard suggest that the Early Palaeozoic and Late Proterozoic successions exposed elsewhere on Svalbard may also be underlain by Grenvillian or older basement rocks. Relationships to other Grenvillian and older terrains in the Arctic are reviewed.  相似文献   

15.
The possibilities of using the average compositions of tonalite–trondhjemite–granodiorite association rocks (TTG), which make up a significant part of the Archaean continental crust, have been examined. The results of the TTG average compositions obtained by other researchers and the authors' data of the average compositions of TTG from the Baltic and Ukrainian shields and the entire Archaean crust are given. It is shown that the average compositions of the Archaean TTG of continental large crustal fragments (cratons or provinces) practically do not bear any information on their sources or conditions of their formation. The possibility of obtaining of such information by means of analysis of the average compositions of TTG, composing smaller fragments of the crust, exemplified by rocks of the Karelian subprovinces of the Baltic Shield has been demonstrated.  相似文献   

16.
我国前寒武纪变质岩的构造特征   总被引：3，自引：0，他引：3  
我国前寒武纪变质岩系的主要构造变形特征是:线型韧性剪切带及逆冲推覆构造发育,一般都遭受了多期变形、变质和强烈的构造置换作用,显生宙再造作用强烈,发育各种类型的穹隆构造。这些特征反映了前寒武纪地壳结构的不均一性和水平运动为主的构造体制.据构造置换、构造组合样式等划分出五种变质岩系构造类型,并对它们的制图原则和研究方法,作了相应的讨论。  相似文献   

17.
The Precambrian metamorphic complex in the southern portion of Wind River Canyon is interpreted as being a fragment of an Archaean greenstone belt. The sequence is composed of meta-sediments inferred to have been various types of pelites and psammites, including graywackes and shales, and a silicate facies banded-iron formation. Meta-volcanics are represented by massive amphibolites.The area has undergone three periods of roughly coaxial folding that represent a single tectonic pattern. A period of intrusion of leucogranite with associated pegmatites separates the first two periods of deformation. These rocks appear to have been derived anatectically from sialic material at greater depth, suggesting the possibility of a sialic basement on which the greenstone belt rocks accumulated. Boudinage of the country rocks can be correlated with either or both of the first two folding episodes, and boudinage of the intrusive rocks occurred with different styles in the axial surfaces of the second and third generation folds.One period of amphibolite-facies metamorphism corresponds to the first and second deformational phases. Minor retrograde effects, fracture fillings, and small-scale metasomatism occurred either in the waning stages of the metamorphism or during a minor subsequent thermal event.Numerous Archaean ages from the Wyoming Precambrian province place Wind River Canyon in a region where examples of such greenstone belts might be expected. As no young intrusive or tectonic events have been reported from the area, the youngest deformational features discussed are considered to be not much younger than reported radiometric dates and therefore not of regional significance.  相似文献   

18.
Several bodies of granulites comprising charnockite, charno-enderbite, pelitic and calc-silicate rocks occur within an assemblage of granite gneiss/granitoid, amphibolite and metasediments (henceforth described as banded gneisses) in the central part of the Aravalli Mountains, northwestern India. The combined rock assemblage was thought to constitute an Archaean basement (BGC-II) onto which the successive Proterozoic cover rocks were deposited. Recent field studies reveal the occurrence of several bodies of late-Palaeoproterozoic (1725 and 1621 Ma) granulites within the banded gneisses, which locally show evidence of migmatization at c. 1900 Ma coeval with the Aravalli Orogeny. We report single zircon ‘evaporation’ ages together with information from LA-ICP-MS U-Pb zircon datings to confirm an Archaean (2905 — ca. 2500 Ma) age for the banded gneisses hosting the granulites. The new geochronological data, therefore, suggest a polycyclic evolution for the BGC-II terrane for which the new term Sandmata Complex is proposed. The zircon ages suggest that the different rock formations in the Sandmata Complex are neither entirely Palaeoproterozoic in age, as claimed in some studies nor are they exclusively Archaean as was initially thought. Apart from distinct differences in the age of rocks, tectono-metamorphic breaks are observed in the field between the Archaean banded gneisses and the Palaeoproterozoic granulites. Collating the data on granulite ages with the known tectono-stratigraphic framework of the Aravalli Mountains, we conclude that the evolution and exhumation of granulites in the Sandmata Complex occurred during a tectono-magmatic/metamorphic event, which cannot be linked to known orogenic cycles that shaped this ancient mountain belt. We present some field and geochronologic evidence to elucidate the exhumation history and tectonic emplacement of the late Palaeoproterozoic, high P-T granulites into the Archaean banded gneisses. The granulite-facies metamorphism has been correlated with the thermal perturbation during the asymmetric opening of Delhi basins at around 1700 Ma.  相似文献   

19.
The information on the composition, structure, P-T conditions of metamorphic facies, evolution, and time of the metamorphic events in the largest Precambrian tectonic provinces of the Antarctic Crystalline Shield gained over more than a half-century is summarized in this paper. The joining up of the ortho- and paracrystalline rocks into complexes and groups according to their geographic position, composition, age, and the character of their metamorphism allowed us to consider the main features of the structure and evolution of the provinces including (1) the near-latitudinal polycyclic Late Precambrian-Early Paleozoic Wegener-Mawson Mobile Belt, extended for more than 4000 km, which started to evolve in the Mesoproterozoic and stabilized only at the end of Cambrian; (2) the Early Precambrian relict crystalline protocratonic blocks adjoining this mobile belt; their history is traced from the Eoarchean; and (3) the near-latitudinal Late Precambrian-Early Paleozoic aulacogen in the southern protocratonic block. The P-T conditions of the metamorphism from the pyroxene-granulite subfacies in the protocratonic blocks to the greenschist facies in aulacogen, as well as the age of the magmatic and metamorphic events in all the tectonic provinces of the shield, are characterized. This made it possible to consider the metamorphic history and conditions of the continental crust’s formation in Antarctica, where the oldest crystalline rocks are dated to the Eoarchean (4060–3850 Ma) and the youngest rocks are ～500 Ma old.  相似文献   

20.
U‐Pb isotopic systems of zircons from the Boobina and Spinaway Porphyries from the Precambrian Pilbara Block of Western Australia indicate ages of 3307± 19 Ma and 2768 ± 16 Ma, respectively. The Boobina Porphyry intrudes upper members of the Archaean greenstones of the Warrawoona Group. The Spinaway Porphyry intrudes basal units of the unconformably overlying volcanics and sediments of the Mt Bruce Supergroup. The age of the Boobina Porphyry, together with previous zircon U‐Pb and whole rock Sm‐Nd age determinations on stratigraphically older units, indicate that early Archaean volcanism in the Pilbara took place between 3560 Ma and 3300 Ma. On the basis of the age determination of the Spinaway Porphyry, and the chronometric definition of 2500 Ma for the Archaean—Proterozoic boundary, by the International Subcommis‐sion on Precambrian Stratigraphy (James H. L. 1978, Precambrian Res. 7, 193–204), the lower units of the Mt Bruce Supergroup should now be assigned to the Archaean.  相似文献   

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