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1.
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
2.
Yvonne Bone 《Mineralium Deposita》1988,23(1):34-41
Tourmalinite is a common rock type associated with Proterozoic strata-bound mineral deposits. Although common, it is often difficult to recognise in the field, leading to misidentification. It occurs as a conformable banded quartz-tourmaline lithological unit comprising at least 15% and as much as 50% of the rock. At Rum Jungle, tourmalinite occurs within the oldest sediments (arenites and magnesites) as distinct lenses, as facies equivalents of quartz-magnetite units and mafic schists (tuffs?) and distal equivalents of polymetallic sulfides. Distinct layering, slump folding, rip-up clasts and the association with diagenetic pyrite suggest a sedimentary environment. Enechelon fracturing of the fine-grained, light green tourmaline crystals spectacularly supports pre-deformation formation. The crystals are optically and chemically zoned parallel to the c axis, with irregular growth lamellae width — which supports a pre-regional metamorphic origin. Analyses show the tourmaline to be the Mg-rich variety “dravite”. Most tourmalinites are interpreted as subaqueous marine deposits. It is more likely that they form in lacustrine, shallow water, evaporitic environments, particularly continental rifts. Suitable B-bearing fluids can be generated by hotspring activity and mobilized by CO2-rich fluids. Association with chemical sediments suggests tourmalinites also have a chemical sediment precursor. Ample evidence at Rum Jungle supports the notion of a continental rift environment, which was the site of deposition of fluvial arenites and alkaline, evaporitic lake sediments. Localised hot-spring activity contributed B-bearing fluids which precipitated chemical sediments according to the pertaining pH, temperature etc. Diagenetic alteration produced the tourmalinite now present. These tourmalinites are comparable to those of similar age elsewhere e.g. Sullivan, Broken Hill. They can be genetically modelled upon Recent borate concentrations, all of which occur in continental rift environments. 相似文献
3.
Maxwell R. Banks A. H. Blissett K. L. Burns B. Campana R. G. Elms I. B. Jennings 《Australian Journal of Earth Sciences》2013,60(2):147-176
Rocks in the Brungle‐Darbalara area of the Tumut Trough form two distinct domains: basement (mainly Bullawyarra Schist), of Cambrian‐Ordovician age, and an Ordovician ‐ Early Silurian sedimentary and volcanic cover sequence. These two domains are separated by a sharp discontinuity that marks an abrupt change in rock type, structure, metamorphic grade and deformation style. Cover sequences have undergone only one major penetrative deformation during the Late Silurian, involving sub‐greenschist facies metamorphism and upright folding. In contrast, the basement also underwent at least two older deformations at greenschist facies and contains distinct high‐strain zones subconcordant with the basement‐cover contact. The high‐strain zones, characterized by a ubiquitous south‐southeast trending mineral lineation, record a discontinuous history of ductile followed by brittle behaviour, consistent with an extensional origin. The structural and metamorphic discontinuity separating basement from Silurian cover is characterized by widespread cataclasis and alteration and is interpreted as a major detachment fault associated with lithospheric extension and the development of the Tumut Trough in the Early Silurian. During the main period of movement on the detachment, which took place prior to intrusion of the Blacks Flat Diorite into the Bullawyarra Schist, mafic and serpentinized ultramafic rocks either were tectonically emplaced or intruded into the high strain zones. This preceded and accompanied extensional faulting of the cover and deposition of Silurian trough sediments and volcanics which unconformably overlie and onlap older units. The development of the Tumut Trough, in the Brungle‐Darbalara area, bears many similarities with that of Cordilleran metamorphic core complexes. Such a model is consistent with environments suggested for the trough by previous workers. The south‐southeast extension direction parallels the trough‐bounding faults and implies an overall strike‐slip tectonic setting. 相似文献
4.
FROM BACK-ARC BASIN TO BACK-ARC FORELAND BASIN—THE SEDIMENTARY BASIN AND TECTONIC EVOLUTION OF THE LATE CALEDONIAN—EARLY HERCYNIAN STAGES IN CORRIDOR AND NORTH QILIAN MTSthenationalNaturalScienceFoundationofChina(No.4 9972 0 78) 相似文献
5.
D. T. Rickard Dr. 《GeoJournal》1979,3(3):235-252
The Baltic shield broadly evolved by successive accretions of younger rocks in a SW direction. The Archaean (>2.5 Ga) basement is situated in the NE of the area and is mantled to the SW by a broad belt of early Proterozoic supracrustals of the Svecokarelian orogen. Over 80% of mined sulfide ores and known reserves in Finland occur on the NE side of a major NW-SE suture, that limits the Archaean basement complex in the SW. These ores, which include the Kotalahti Ni-Cu zone, the Vihanti Zn-Cu-Pb zone and the Outokumpu Cu-Co zone, are emplaced in early Proterozoic epicontinental rocks and obducted ophiolitic slices. The early Proterozoic marine complexes on the SW side of the Archaean continent include the ore districts of the Skellefte field and the Central Province of Sweden and Finland. These ores include complex massive and bedded Pb-Zn-Cu ores, often with pyrite, in island arc settings. The Bergslagen district of the Central Province also includes a large number of small, exhalative-sedimentary iron and manganese ores.Mid-Proterozoic evolution in Scandinavia mostly occurred through vertical movements and the emplacement of late- and an-orogenic granite suites with associated porphyry effusives and continental sandstones. The Kiruna-type iron ores, which accounted for six % of global iron ore production in 1969, probably originated in association with these events.Phanerozoic evolution in Scandinavia was dominated by the formation of the Caledonide orogen. The complex Pb-Cu-Zn ores of the Caledonide Province were formed mainly in an island arc setting during the Ordovician. These units were obducted onto the continental margin, where they suffered complex folding, metamorphism, intrusion and further nappe development during mid-Silurian or early-Devonian times.Intraformational brines, generated in the thick back-arc sedimentary pile during the Ordovician and Silurian, were mobilized in advance of the eastward translation of the Caledonide nappes. Lead and zinc, leached from sediments, were deposited as sulfide ores in sulfidic sandstone aquifers along the E margin of the Caledonide orogen. 相似文献
6.
Pan-African magmatism in the Menderes Massif: geochronological data from leucocratic tourmaline orthogneisses in western Turkey 总被引：1，自引：1，他引：0
O. E. Koralay O. Candan F. Chen C. Akal R. Oberh?nsli M. Sat?r O. ?. Dora 《International Journal of Earth Sciences》2012,101(8):2055-2081
The Menderes Massif, exposed in western Anatolia, is a metamorphic complex cropping out in the Alpine orogenic belt. The metamorphic rock succession of the Massif is made up of a Precambrian basement and overlying Paleozoic-early Tertiary cover series. The Pan-African basement is composed of late Proterozoic metasedimentary rocks consisting of partially migmatized paragneisses and conformably overlying medium- to high-grade mica schists, intruded by orthogneisses and metagabbros. Along the southern flank of the southern submassif, we recognized well-preserved primary contact relationship between biotite and leucocratic tourmaline orthogneisses and country rocks as the orthogneisses represent numerous large plutons, stocks and vein rocks intruded into a basement of garnet mica schists. Based on the radiometric data, the primary deposition age of the precursors of the country rocks, garnet mica schist, can be constrained between 600 and 550?Ma (latest Neoproterozoic). The North Africa–Arabian-Nubian Shield in the Mozambique Belt can be suggested as the possible provenance of these metaclastics. The intrusion ages of the leucocratic tourmaline orthogneisses and biotite orthogneisses were dated at 550–540?Ma (latest Neoproterozoic–earliest Cambrian) by zircon U/Pb and Pb/Pb geochronology. These granitoids represent the products of the widespread Pan-African acidic magmatic activity, which can be attributed to the closure of the Mozambique Ocean during the final collision of East and West Gondwana. Detrital zircon ages at about 550?Ma in the Paleozoic muscovite-quartz schists show that these Pan-African granitoids in the basement form the source rocks of the cover series of the Menderes Massif. 相似文献
7.
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
8.
WilliamS.FYFE 《《地质学报》英文版》1999,73(1):1-7
The Jiaodong gold province is situated in the eastern Sino-Korean Platform within the so-calledJiaoliao Uplift. The basement rocks are Archaean and Proterozoic metamorphic rocks. Mesozoic sedimentary andvolcanic cover occur within extensional basins. Intrusive rocks are dominated by Mesozoic granitoid, with interme-diate-acid and basic dyke swarms. The structures form an E-W-trending anticlinorium in the basement complex, andlarge-scale NE-SW-and NNE-SSW-trending fault zones of Mesozoic age. The gold mineralization is associated withthe Mesozoic faults and related secondary fractures in the granites or granite-basement contacts. The mineralizationtypes are quartz-vein type and wall-rock alteration type. Wall-rock alteration is very well developed around the orezones. Alteration minerals include quartz, sericite (and fuchsite), pyrite, calcite, chlorite, hematite, rutile and graph-ite. The ore assemblage is uniform in all deposits, including pyrite, chalcopyrite, galena, sphalerite, arsenopyrite,pyrrhotite, gold, electrum, hessite, petzite, magnetite, molybdenite, tetrahedrite and wolframite. Mesozoic collisionand subduction between the South China and North China continental blocks contributed to formation of the Meso-zoic granitoid intrusions. The granitic magma is considered to be derived from partial melting of the crust throughunderplating processes. Gold was remobilised from basement rocks and deposited in fracture zones by the high-temperature fluids associated with these processes. 相似文献
9.
PETROLOGY AND AGE OF THE KINNAR KAILAS GRANITE:EVIDENCES FOR AN ORDOVICIAN POST-OROGENIC EXTENSION IN THE HIGHER HIMALAYAN CRYSTALLINE, SUTLEJ, INDIA 相似文献
10.
本文依据1∶25万区域地质调查成果资料,从昆中断裂带对南北两侧的基底变质岩系(包括变基性火山岩、变泥质岩)、表壳盖层沉积岩系、前寒武纪长英质火成侵入岩以及镁铁-超镁铁质侵入岩的沉积建造、岩石类型组合、岩石地球化学及所反映的源岩物性的控制,系统对比讨论了昆中断裂带南北两侧基底陆块特征及昆中断裂带的构造属性。得出以昆中断裂带为界,南北两侧陆块的大陆岩石圈,无论在表壳沉积岩系、中-下地壳和地幔的层性和物性结构及地球化学成分都存在显著差异。从而提出昆仑造山带实际上是个两陆块碰撞复合陆缘造山带。在元古宇以前南北陆块并非属同一古陆块,或者说昆中断裂带为欧亚大陆和冈瓦纳大陆的真正分界或二者的拼合带。 相似文献
11.
Gold mineralization in Archaean granite-greenstone environments, especially gold-quartz veins, contributes considerably to the world's gold production. The formation of epigenetic gold mineralization in greenstone belts is generally explained by the metamorphic secretion theory. This theory is based on the assumption that the source of the gold may be komatiitic or tholeiitic lavas, pyritic chemical or clastic sediments and even granitic rocks from which, as a result of regional metamorphic overprinting, gold was extracted and concentrated in suitable structures.It has been shown that in proposed potential source rocks, gold is predominantly associated with sulfide minerals and thus relatively easily accessible to secretion and reconstitution processes.A large number of various rock types originating from granite-greenstone terranes of the Kaapvaal and the Rhodesian cratons were geochemically investigated, and the following ranges for gold determined:volcanic rocks (komatiitic and tholeiitic): 0.1–372 ppbgranitic rocks of the basement: 0.3–7.8 ppbiron-rich chemical sediments: 1.0–667 ppbStatistical treatment of the data reveals that volcanic rocks as well as iron-rich chemical sediments are favorable sources for epigenetic gold mineralization formed by metamorphic secretion, while the granitic rocks make less suitable primary gold sources. This finding explains the close spatial relationship which is common between gold-quartz veins and greenstone belts. The conspicuous abundance of epigenetic gold mineralization in the Archaean, however, is attributed to the unique geologic and metamorphic history of the granite-greenstone terranes. 相似文献
12.
Single zircon ages from high-grade rocks of the Jianping Complex, Liaoning Province, NE China 总被引：13，自引：0，他引：13
The high-grade rocks of the Jianping Complex in Liaoning Provi nce, NE China, belong to the late Archaean to earliest Proterozoic granulite belt of the North China craton. Single zircon ages obtained by the Pb–Pb evaporation method and SHRIMP analyses document an evolutionary history that began with deposition of a cratonic supracrustal sequence some 2522–2551 Ma ago, followed by intrusion of granitoid rocks beginning at 2522 Ma and reaching a peak at about 2500 Ma. This was followed by high-grade metamorphism, transforming the existing rocks into granulites, charnockites and enderbites some 2485–2490 Ma ago. The intrusion of post-tectonic granites at 2472 Ma is associated with widespread metamorphic retrogression and ends the tectono–metamorphic evolution of this terrain. A similar evolutionary sequence has also been recorded in the granulite belt of Eastern Hebei Province. We speculate that the Jianping Complex was part of an active continental margin in the late Archaean that became involved in continental collision and crustal thickening shortly after its formation. There is a remarkable similarity between the 2500 Ma North China granulite belt and the equally old granulite belt of Southern India, suggesting that the two crustal domains could have been part of the same active plate margin in latest Archaean times. 相似文献
13.
华北地台的元古宙构造演化 总被引：3，自引：0，他引：3
华北地台在前寒武纪经历过三个大构造阶段,即太古初始克拉通、早元古代原地台和中—晚元古代地台的形成阶段,每个阶段都有各具特点的构造演化史。发生在太古宙末期的阜平运动,是一次强烈的构造-热事件,造成太古岩层的变质、变形等和形成初始的克拉通基底,早元古时出现了裂陷形成了克拉通内或边缘的内硅铝盆地或海槽。早元古末期的吕梁-中条运动是另一次重要的构造-热事件,此后,原地台最终固化,华北地台的主要构造格架基本成型。中—晚元古时期在华北地台的不同部位发育了三个主要构造盆地。 相似文献
14.
湖屯铅锌矿主要产于中-晚元古代变质岩基底与火山岩接触部位或“天窗”内外,矿体呈脉状、透镜状、似层状,受变质岩层位与后期断裂构造控制,矿床成因类型为海底火山喷发-沉积变质（热液改造）块状硫化物型和构造蚀变岩型硫化物矿床。区内异常范围大,浓度高,成矿条件好。 相似文献
15.
E.M. Lazko V.P. Kiriluk V.I. Lashmanov A.M. Lyssak A.A. Sivoronov G.M. Jatsenko 《Precambrian Research》1978,6(2):223-233
Soviet geologists consider the Precambrian to be divided into two groups — Archaean and Proterozoic; but such a division is unsatisfactory. A major unconformity separates Proterozoic volcanic and sedimentary formations from an underlying sequence that contains two supergroups of supercrustal formations. The oldest of these is unanimously considered to be Archaean. Rocks of that supergroup play an essential part in the composition of the Baltic, Ukrainian, Aldan and Anabar Shields and of the ancient fold belts of the East-European and Siberian platforms.Distinctive features in the composition, tectonic structure, metamorphism and metallogeny of Archaean complexes lead to the conclusion that they were formed in specifically mobile areas, different from geosynclinal areas.The other supergroup of high-grade metamorphic rocks has no clear place in the accepted two-fold stratigraphic scheme of the Precambrian, and it is considered sometimes to be Archaean and sometimes to be Early Proterozoic. We propose restoring the forgotten name “Eozoic” for that supergroup. Eozoic complexes are characterized by peculiarities of composition and inner structure, which signify changes in the tectonic regime of the earth at the lower and upper boundaries of the Eozoic Supergroup. These peculiarities give grounds for distinguishing the Eozoic Supergroup as an independent stratigraphic division.The Stanovoy Complex of the southern part of the Aldan Shield is a stratotype for the Eozoic Supergroup. Many well-known stratigraphic subdivisions of the Siberian Platform (e.g., the Eniseiskaya, the Birusinskaya series and others), the Taratash Complex of the Urals, the Goranskaya and Shahdarinskaya series of the South-West Pamir, the Tikitch complex and Aulskaya series of the Ukrainian Shield, and in part the Belomorsky Complex of the Baltic Shield, as well as some others, are also Eozoic.The Eozoic complexes are characterized by the following specific features: only some supercrustal formations are typical for them; the small number of rock types which have a total thickness about 5–6 km; relatively monotonous mineral composition of the rocks; variable quantitative ratios of rocks; absence of contrasting marker beds; regional metamorphism and ultrametamorphism in the amphibolite facies; wide development of ultrametamorphic granitoids and migmatites; distinct tectonic differentiations of the basin of sedimentation.Dates determined by isotopic analyses, which mostly reflect the metamorphism of the deposits, fall predominantly in the range 2600–3100 Ma. 相似文献
16.
17.
Five suites of rocks collected from the Precambrian basement in the NE Bayuda Desert of central northern Sudan give late Proterozoic whole-rock isochron ages. The Abu Harik Complex, thought by some previous workers to be an older basement, gives an age of 898 ± 51 Ma. Upper amphibolite-facies metasediments give a metamorphic age of 761 ± 22 Ma. The supposedly younger greenschist-facies El Koro Volcanic Series were erupted 800 ± 83 Ma ago. These are chemically similar to the volcanics which unconformably overlie the Sol Hamed ophiolite in the Red Sea Hills of NE Sudan and to some modern island are volcanics. The metasediments were intruded 678 ± 43 Ma ago by the Diefallab Granite, which is itself deformed. The younger, weakly-deformed Amaki Series, with a basal conglomerate containing basement clasts overlain by purple grits, is probably equivalent to the molasse-type Hammamat Group of the Eastern Desert of Egypt which was deposited between 616 and 596 Ma ago. Finally, the post-tectonic Shallal Granite, with within-plate geochemistry, was intruded 549 ± 12 Ma ago. Geochemical data suggest that the Abu Harik Complex, the El Koro Volcanic Series and the Diefallab Granite are arc-related magmatic rocks. They were intruded into, or thrust onto, shallow-water, shelf sediments during subduction and then collision, between c. 900 and 550 Ma. The data presented here give no support to previous views that the high-grade metasediments were metamorphosed prior to the late Proterozoic events, that they unconformably overlie a still older, perhaps Archaean, basement or that they are unconformably overlain by younger late Proterozoic low-grade volcanics. The Precambrian rocks along the E side of the Bayuda Desert must now all be assigned to the late Proterozoic and the boundary between this late Proterozoic fold belt and an older craton, known to crop out at Jebel Uweinat, must lie farther to the W. 相似文献
18.
Tore Torske 《International Journal of Earth Sciences》1982,71(1):104-119
An isolated synclinorium, comprising the up to 5 km thick Ullensvang Group of metavolcanic and metasedimentary rocks, is surrounded by granitoid plutons and has no recognizable older basement. From an earlier interpretation based on regional data this area is inferred to be part of a Proterozoic, cordilleran-type volcanic-plutonic belt. Major structures in the synclinorium are interpreted to have evolved as follows: 1) Early folds were produced by regional compression; 2) within a part of the synclinorium, such folds were tightened and reoriented during a subsequent deformation phase caused by forceful emplacement of the Kvinnherad batholith, flanking the synclinorium to the southwest; 3) this deformation was accompanied by thrust faulting towards the northeast, away from the batholith; 4) forceful emplacement of plutons belonging to the Eidfjord-Kinsarvik batholith, on the northeastern flank of the synclinorium, produced southwest-vergent overfolding of the earlier structures in the synclinorium. In addition, local deformation around a pluton intruding the northern part of the synclinorium near Utne produced areally restricted deformation structures, approximately corresponding in time with the second deformation event (2) above. Structures in plutonics rocks of the batholiths are interpreted in terms of an emplacement model involving distension diapirism. The deformation zones associated with diapiric plutons in this area appear to be more similar to some of those reported from Archaean greenstone belts than to those found in volcanic-plutonic belts of younger cordilleran-type orogens. 相似文献
19.
地史早期岩石中的铅锌演化--狼山-渣尔泰山中元古代铅锌成矿的物质基础 总被引：2，自引：0，他引：2
以中国内蒙古狼山一渣尔泰山中元古代SEDEX型铅．锌成矿带为例，研究了该区从太古代到中元古代地壳岩石的铅锌含量和变化关系以及与成矿的关系。研究发现，从早到晚，岩石SiO2和K2O含量升高，铅含量也与二者同步增加；FeO、MgO、CaO及Na20含量呈下降趋势，锌含量也同步降低。在太古代时，岩石的Zn／Pb比值一般〉8，中元古代时这一比值降低为2～4。矿石的Zn／Pb比值与基底岩石Zn／Pb比值具有很好的一致性。铅锌这种随时间的变化与中元古代铅的暴发性成矿及大规模铅锌共生矿床的形成是同步的，说明基底岩石中的铅和锌是该成矿带SEDEX矿床成矿的物质基础。 相似文献
20.
The eastern margin of the East European Craton (EEC) has a long lasting geological record of Precambrian age. Archaean and Proterozoic strata are exposed in the western fold-and-thrust belt of the Uralides and are known from drill cores and geophysical data below the Palaeozoic cover in the Uralides and its western foredeep. In the southern Uralides, sedimentary, metamorphic and magmatic rocks of Riphean and Vendian age occur in the Bashkirian Mega-anticlinorium (BMA) and the Beloretzk Terrane. In the eastern part of the BMA (Yamantau anticlinorium) and the Beloretzk Terrane, K-Ar ages of the <2-µm-size fraction of phyllites (potassic white mica) and slates (illite) give evidence for a complex pre-Uralian metamorphic and deformational history of the Precambrian basement at the southeastern margin of the EEC. Interpretation of the K-Ar ages considered the variation of secondary foliation and the diagenetic to metamorphic grade. In the Yamantau anticlinorium, the greenschist-facies metamorphism of the Mesoproterozoic siliciclastic rocks is of Early Neoproterozoic origin (about 970 Ma) and the S1 cleavage formation of Late Neoproterozoic (about 550 Ma). The second wide-spaced cleavage is of Uralian origin. In the central and western part of the BMA, the diagenetic to incipient metamorphic grade developed in Late Neoproterozoic time. In post-Uralian time, Proterozoic siliciclastic rocks with a cleavage of Uralian age have not been exhumed to the surface of the BMA. Late Neoproterozoic thrusts and faults within the eastern margin of the EEC are reactivated during the Uralian deformation. 相似文献