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1.
The role of the Lurio Belt in northern Mozambique, and the geological evolution of its foreland in the Proterozoic are discussed in the light of recent, single zircon age determinations showing Pan-African age for the granulite-facies metamorphism. The following tentative conclusions are reached, and evidence for and against them is reviewed. The Lurio Belt had a two-fold history, as a crust-forming orogen during the Kibaran and as a transpressive suture in Pan-African times. Together with the Zambezi Belt and the Schlesien-Mwembeshi Lineament, it formed a 3000 km discontinuity which underwent an embryonic oceanic development before being sutured during the Pan-African collisional event. The Lurio Belt foreland had a tectonic-metamorphic evolution at ca 1000 Ma, prior to major, Pan-African overprinting and was probably continuous with the basement of Queen Maud Land (Antarctica) and Natal. In Pan-African times, clockwise transpressive movements along the Lurio Belt brought about emplacement of granulite klippen in its foreland. If there is a southward continuation of the Pan-African Mozambique Belt beyond Mozambique, it is probably to be found in Antarctica.  相似文献   

2.
Whole rock major and trace element data from granitoids adjacent to the Kalahari Craton–Mozambique–Maud Belt boundary are described. The data from ～1140 Ma old granodioritic and ～1110 Ma old granitic bodies in the Mozambique Belt show that they are typical of calc-alkaline and A-type granitoids respectively. Radiogenic Rb/Sr and Sm/Nd isotope data from the two granitoid bodies suggest significant older crustal contributions during their genesis. The granodioritic gneisses show TDM model ages of ～2100–3500 Ma whereas megacrystic granitic gneisses have TDM model ages of ～1600–3100 Ma. Granite from the Archaean-age Kalahari Craton has TDM model ages of ～3000–3500 Ma.The data from Mozambique are compared with whole rock major and trace element chemistry and U/Pb zircon SHRIMP data from the Maud Belt in western Dronning Maud Land. These show that ～1140 Ma old granodioritic gneisses in Sverdrupfjella and Kirwanveggan have similar ages and chemical compositions to similar rocks in central Mozambique. Radiogenic isotope characteristics of the gneisses from central Mozambique and Sverdrupfjella are similar and suggest older crustal contributions in contrast to the juvenile nature of the gneisses from Kirwanveggan.Similarly, ～1090 Ma old granitic gneisses from central Mozambique, Sverdrupfjella and Kirwanveggan have similar ages and A-type chemical compositions. In contrast the radiogenic isotope compositions from Kirwanveggan are juvenile whereas those from central Mozambique show a significant older crustal contribution.The whole rock radiogenic isotope data can be interpreted to suggest that the Mesoproterozoic Mozambique Belt rocks were generated by partial melting which probably involved mixing of Archaean/Paleoproterozoic crust and younger Mesoproterozoic juvenile magma at ～1100 Ma and suggest that the Kalahari Craton probably extends eastwards at depths for more than 30 km from its exposure at surface.The data support correlations between the Mozambique Belt and the Maud Belt in Antarctica in general and more specifically show similarities between the Kalahari Craton boundary and the Mozambique–Maud Belt in lithologies immediately adjacent to that boundary.Two episodes of anatectic migmatisation are recognized in rocks from the Mozambique Belt in central Mozambique. These show an earlier migmatitic vein phase oriented parallel to the planar foliation in the granitic and tonalitic gneisses and a later discordant vein phase which is oriented parallel to localized but intense N–S oriented shearing along the Kalahari Craton/Mozambique Belt boundary zone. SHRIMP zircon data from the younger migmatitic vein phase suggests a crystallization age of 997 ± 4 Ma. Small numbers of inherited zircons have ages of ～2700 Ma and ～1100–1200 Ma. Younger discordant analyses suggesting metamorphic disturbance between ～400 Ma and 550 Ma are seen. The data imply the high strain along the eastern margin of the Kalahari Craton in the Manica area, occurred at ～1000 Ma and not at ～450 Ma as was previously thought. The data suggest the Pan African deformation and metamorphism in the area involved minor reworking. The undeformed to weakly deformed Tchinadzandze Granodiorite intruded into the Kalahari Craton has an age of 2617 ± 16 Ma.  相似文献   

3.
The Mozambique Belt (MB) of the East Africa Orogen contains large areas of granulite-facies migmatitic gneisses with Archaean and Palaeoproterozoic protolith ages and that were recycled during the Neoproterozoic Pan-African orogeny. The study area is situated along the Great Ruaha River and within the Mikumi National Park in central Tanzania where migmatitic gneisses and mafic to intermediate granulites are interlayered with Neoproterozoic granulite-facies migmatitic metapelites. Mineral textures suggest isothermal decompression, with the peak mineral assemblage comprising Grt–Bt–Ky–Kfs–Pl–Qtz ± Phn ± Ti-Oxide ± melt and amphibolite-facies retrograde assemblage Grt–Bt–Sil–Ms–Kfs–Pl–Qtz ± Fe–Ti-Oxide. The near isothermal retrograde overprint is seen in well-developed formation of pseudomorphs after garnet. The HP granulite-facies assemblages record P–T conditions of 13–14 kbar at 760–800 °C. Retrogression and the release of fluids from crystallizing melts occurred at 7 kbar and 650–700 °C. A fluid inclusion study shows three types of fluid inclusion consisting of nearly pure CO2, as well as H2O–NaCl and H2O–CO2 mixtures. We suggest that a immiscible CO2-bearing brine represents the fluid composition during high-grade peak metamorphism, and that the fluid inclusions containing H2O–NaCl or nearly pure CO2 represent trapped fluids from in situ crystallised melt. The results suggest strong isothermal decompression, which is probably related to a fast exhumation after crustal thickening in the central part of the Mozambique Belt in Tanzania.  相似文献   

4.
Central Gondwana was assembled by three continental collisions in relatively quick succession: late Cryogenian East Africa Orogen, early Ediacaran West Antarctica Orogen and late Ediacaran Kuunga Orogen. The Kuunga Orogen involved diachronous closure of the South Adamastor–Khomas–Mozambique Oceans and accretion of Kalahari Craton and cratonic elements in Antarctica, with a previously assembled North Gondwana. The two older orogens were still hot and deforming at the time of final assembly by the Kuunga Orogen, and were therefore reworked and re-metamorphosed. The Central Kuunga Orogen is comprised of the Lufilian Arc, Zambezi Belt, Malawi–Unango Complex and the Lurio Belt. This region was the site of earliest collision in the Kuunga Orogen at ~575 Ma, and involved collision of two buoyant, previously metamorphosed rigid basement promontories. Pivoting on the Zambezi Belt indenters led to clockwise rotation of the Kalahari Craton and oblique collision within the Damara Belt ~20–30 m.y. later. The Central Kuunga Orogen is a relatively cold collisional belt dominated by eclogite, whiteschist and Barrovian series metamorphic parageneses, and contrasts with the paired metamorphic response in the Damara Belt to the west, and low-P/high-T metamorphism in the East Kuunga Orogen. Metamorphic parageneses are preserved from each stage of the full Wilson Cycle: from initiation of continental lithosphere thinning at ~940 Ma, widespread rifting between 725 and 805 Ma, and passive margin sedimentation until ~580 Ma. Eclogite-facies subduction parageneses indicate consumption of ocean lithosphere was underway by ~630–660 Ma. Collision at ~575 Ma involved deep burial of continental crust and formation of very high-P, low T/depth metamorphic parageneses, followed by Barrovian series thermal peaks at ~545 and ~525 Ma. Isostatic compensation and stress switches associated with plate reconfigurations once Gondwana was assembled, resulted in exhumation and local extension in an intra-continental setting from ~518 Ma.  相似文献   

5.
Extensive high-grade polydeformed metamorphic provinces surroundingArchaean cratonic nuclei in the East Antarctic Shield recordtwo tectono-thermal episodes in late Mesoproterozoic and lateNeoproterozoic–Cambrian times. In Western Dronning MaudLand, the high-grade Mesoproterozoic Maud Belt is juxtaposedagainst the Archaean Grunehogna Province and has traditionallybeen interpreted as a Grenvillian mobile belt that was thermallyoverprinted during the Early Palaeozoic. Integration of newU–Pb sensitive high-resolution ion microprobe and conventionalsingle zircon and monazite age data, and Ar–Ar data onhornblende and biotite, with thermobarometric calculations onrocks from the H.U. Sverdrupfjella, northern Maud Belt, resultedin a more complex P–T–t evolution than previouslyassumed. A c. 540 Ma monazite, hosted by an upper ampibolite-faciesmineral assemblage defining a regionally dominant top-to-NWshear fabric, provides strong evidence for the penetrative deformationin the area being of Pan-African age and not of Grenvillianage as previously reported. Relics of an eclogite-facies garnet–omphaciteassemblage within strain-protected mafic boudins indicate thatthe peak metamorphic conditions recorded by most rocks in thearea (T = 687–758°C, P = 9·4–11·3kbar) were attained subsequent to decompression from P >12·9 kbar. By analogy with limited U–Pb singlezircon age data and on circumstantial textural grounds, thisearlier eclogite-facies metamorphism is ascribed to subductionand accretion around 565 Ma. Post-peak metamorphic K-metasomatismunder amphibolite-facies conditions is ascribed to the intrusionof post-orogenic granite at c. 480 Ma. The recognition of extensivePan-African tectonism in the Maud Belt casts doubts on previousRodinia reconstructions, in which this belt takes a pivotalposition between East Antarctica, the Kalahari Craton and Laurentia.Evidence of late Mesoproterozoic high-grade metamorphism duringthe formation of the Maud Belt exists in the form of c. 1035Ma zircon overgrowths that are probably related to relics ofgranulite-facies metamorphism recorded from other parts of theMaud Belt. The polymetamorphic rocks are largely derived froma c. 1140 Ma volcanic arc and 1072 ± 10 Ma granite. KEY WORDS: Maud Belt; Pan-African orogeny; geochronology; P–T–t path, East Antarctica  相似文献   

6.
A single zircon geochronological study of gneisses from the Obudu Plateau of southeastern Nigeria, using the evaporation technique, indicates that zircons recorded several Precambrian high-grade metamorphic events (Eburnean and Pan-African). Igneous and multifaceted metamorphic zircons yielded 207Pb/206Pb ages of 2062.4 ± 0.4 Ma, 1803.8 ± 0.4 Ma and 574 ± 10 Ma, respectively and confirm for the first time that granulite-facies metamorphism affected the basement of southeastern Nigeria, resulting in the formation of charnockites and granulitic gneisses. The Pan-African high-grade event was coeval with the formation of granulites in Cameroon, Togo and Ghana and resulted from collisional processes during continental amalgamation to form the Gondwana supercontinent. The sources of the sediments, which were deposited at ≈605 Ma and metamorphosed at 574 Ma, comprise older igneous and metamorphic protoliths (including inherited xenocrystic zircons up to 2.5 Ga in age). The Palaeoproterozoic zircons seem to have survived Pan-African melting.  相似文献   

7.
An age of 3112 ± 6 (2σ) Ma, determined by conventional techniques on single zircons from a felsic volcanic rock from the Sholl Belt in the western part of the Archaean Pilbara Craton of Western Australia, is interpreted as the age of felsic volcanism. This is about 100 Ma older than felsic volcanic rocks in the nearby but unconnected Whim Creek Belt and is significantly younger than felsic volcanism in the East Pilbara, which took place during two distinct episodes at 3450 Ma and 3300 Ma. The present results rule out previous correlations between the felsic volcanic rocks of the Sholt Belt and the 3452 ± 16 Ma old Duffer Formation in the East Pilbara.  相似文献   

8.
A metamorphic petrological study, in conjunction with recent precise geochronometric data, revealed a complex P–T–t path for high-grade gneisses in a hitherto poorly understood sector of the Mesoproterozoic Maud Belt in East Antarctica. The Maud Belt is an extensive high-grade, polydeformed, metamorphic belt, which records two significant tectono-thermal episodes, once towards the end of the Mesoproterozoic and again towards the late Neoproterozoic/Cambrian. In contrast to previous models, most of the metamorphic mineral assemblages are related to a Pan-African tectono-thermal overprint, with only very few relics of late Mesoproterozoic granulite-facies mineral assemblages (M1) left in strain-protected domains. Petrological and mineral chemical evidence indicates a clockwise P–T–t path for the Pan-African orogeny. Peak metamorphic (M2b) conditions recorded by most rocks in the area (T = 709–785 °C and P = 7.0–9.5 kbar) during the Pan-African orogeny were attained subsequent to decompression from probably eclogite-facies metamorphic conditions (M2a).The new data acquired in this study, together with recent geochronological and geochemical data, permit the development of a geodynamic model for the Maud Belt that involves volcanic arc formation during the late Mesoproterozoic followed by extension at 1100 Ma and subsequent high-grade tectono-thermal reworking once during continent–continent collision at the end of the Mesoproterozoic (M1; 1090–1030 Ma) and again during the Pan-African orogeny (M2a, M2b) between 565 and 530 Ma. Post-peak metamorphic K-metasomatism under amphibolite-facies conditions (M2c) followed and is ascribed to post-orogenic bimodal magmatism between 500 and 480 Ma.  相似文献   

9.
New SHRIMP zircon data from Gjelsvikfjella and Mühlig–Hofmann–Gebirge (East Antarctica) indicate that the metamorphic basement is composed of Grenville-age rocks that are most likely part of the north-eastern continuation of the Namaqua–Natal–Maud Belt. Crystallisation ages of meta-igneous rocks range between ca. 1,150 to 1,100 Ma, with little inheritance recorded. Metamorphic zircon overgrowth during high-grade metamorphism is dated between ca. 1,090 to 1,050 Ma. Both, the crystallisation ages and the metamorphic overprint are similar to U–Pb data from a number of areas along a ca. 2,000-km stretch from Natal in South Africa to central Dronning Maud Land. The basement underwent in part strong high-grade reworking during the collision of East and West Gondwana at ca. 550 Ma. The timing of Grenville-age metamorphism has important implications for the position of Kalahari in Rodinia. It also questions that Coats Land is part of the Maud Belt because the undeformed volcanic rocks of Coats Land are older than the main metamorphism within the Maud Belt and, therefore, must rest on older basement. This interpretation explains why the pole of Coats Land at ca. 1,110 Ma differs from the Kalahari poles by 30°, i.e. Coats Land had not yet amalgamated to Kalahari. On the other hand, the palaeopoles from Coats Land and Laurentia at 1,110 Ma are identical within error. Thus, Coats Land could have been part of Laurentia prior to the final amalgamation of Rodinia, the Namaqua–Natal–Maud Belt could have been a part of the Grenville Belt and the entire Kalahari Craton could indeed have opposed Laurentia on its eastern side.  相似文献   

10.
The Zambezi Belt in southern Africa has been regarded as a part of the 570-530 Ma Kuunga Orogen formed by a series of collision of Archean cratons and Proterozoic orogenic belts.Here,we report new petrological,geochemical,and zircon U-Pb geochronological data of various metamorphic rocks(felsic to mafic orthogneiss,pelitic schist,and felsic paragneiss) from the Zambezi Belt in northeastern Zimbabwe,and evaluate the timing and P-T conditions of the collisional event as well as protolith formation.Geochemical data of felsic orthogneiss indicate within-plate granite signature,whereas those of mafic orthogneiss suggest MORB,ocean-island,or within-plate affinities.Metamorphic P-Testimates for orthogneisses indicate significant P-T variation within the study area(700-780 C/6.7-7.2 kbar to 800-875 C/10-11 kbar) suggesting that the Zambezi Belt might correspond to a suture zone with several discrete crustal blocks.Zircon cores from felsic orthogneisses yielded two magmatic ages:2655±21 Ma and 813士5 Ma,which suggests Neoarchean and Early Neoproterozoic crustal growth related to within-plate magmatism.Detrital zircons from metasediments display various ages from Neoarchean to Neoproterozoic(ca.2700-750 Ma).The Neoarchean(ca.2700-2630 Ma) and Paleoproterozoic(ca.2200-1700 Ma) zircons could have been derived from the adjacent Kalahari Craton and the Magondi Belt in Zimbabwe,respectively.The Choma-Kalomo Block and the Lufilian Belt in Zambia might be proximal sources of the Meso-to Neoproterozoic(ca.1500-950 Ma) and early Neoproterozoic(ca.900-750 Ma) detrital zircons,respectively.Such detrital zircons from adjacent terranes possibly deposited during late Neoproterozoic(744-670 Ma),and subsequently underwent highgrade metamorphism at 557-555 Ma possibly related to the collision of the Congo and Kalahari Cratons during the latest Neoproterozoic to Cambrian.In contrast,670-627 Ma metamorphic ages obtained from metasediments are slightly older than previous reports,but consistent with~680-650 Ma metamorphic ages reported from different parts of the Kuunga Orogen,suggesting Cryogenian thermal events before the final collision.  相似文献   

11.
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   

12.
A polycyclic two-stage corona growth in the Iforas Granulitic Unit (Mali)   总被引：2，自引：0，他引：2  
Abstract Retrograde and prograde mineral assemblages from metapelitic and metabasic rocks of the Iforas Granulitic Unit (Mali) were generated by the superimposition of two granulite facies metamorphic events. They clearly result from a polycyclic evolution and can be related to a late Eburnean unroofing followed by a Pan-African burial.
Thermobarometry on Pan-African garnet-bearing assemblages yields ( P, T ) estimates of 620±50°C and 5± Ikbar. The nearly anhydrous conditions produced in the Eburnean appear to be the direct cause of the unusually lowtemperature granulite-facies metamorphism in the Pan-African. These P, T estimates are compared with those obtained on the underlying unit (Kidal Assemblage) upon which the Iforas Granulitic Unit was thrust. A P-T-t path, during the Pan-African orogeny, is proposed and discussed for both the Iforas Granulites and Kidal Assemblage.  相似文献   

13.
《Gondwana Research》2001,4(3):329-336
Granulites from the Usambara, Wami River and Uluguru areas in the northern part of the Mozambique Belt in Tanzania yield Sm-Nd garnet — whole rock ages of between 580 and 634 Ma with a mean of 609 ± 11 Ma (2σ). This mean age is only slightly younger than the previously published peak metamorphic age of 641 ± 2 Ma, suggesting that, contrary to some earlier arguments, garnet Sm-Nd ages can be used to closely constrain the age of peak metamorphism even in slowly cooled terranes. Using published peak metamorphic temperatures of ∼810°C and cooling rates of 1–4°C/Ma, the mean age translates into garnet closure temperatures of 690 to 780°C.The similarity in garnet ages over widely separated areas, coupled with the previously established similarity in equilibrium PT conditions, indicate that isolated complexes that form the Eastern Granulites in the Tanzanian sector of the Mozambique Belt share the same thermal history and were formed under the same geodynamic setting.A few published garnet ages of between 525 and 545 Ma indicate a younger, less pervasive event of granulite facies metamorphism in the Belt. The bimodal distribution of garnet ages supports a previously published hypothesis that the assembly of Gondwana took place in two stages. The ∼610 Ma old ages most likely date cooling from granulite facies metamorphism arising from regional crustal thickening associated with the amalgamation of India, Madagascar, parts of eastern Antarctica, the Kalahari craton, the Congo craton and the Arabian-Nubian shield (forming the IMSLEK-ANS collage). On the other hand, the 525–545 Ma ages may mark cooling from a thermal event associated with the collision of Australo-Antarctica with the IMSLEK-ANS collage.  相似文献   

14.
Pan‐African high‐pressure granulites occur as boudins and layers in the Lurio Belt in north‐eastern Mozambique, eastern Africa. Mafic granulites contain the mineral assemblage garnet + clinopyroxene + plagioclase + quartz ± magnesiohastingsite. Garnet porphyroblasts are zoned with increasing almandine and spessartine contents and decreasing grossular and pyrope contents from core (Alm46Prp32Grs21Sps2) to rim (Alm52Prp26Grs19Sps3). This pattern is interpreted as a retrograde diffusion zoning with the preserved core chemistry representing the peak metamorphic composition. Mineral reaction textures occur in the form of monomineralic and composite plagioclase ± orthopyroxene ± amphibole ± biotite ± magnetite coronas around garnet porphyroblasts. Thermobarometry indicates peak metamorphic conditions of up to 1.57 ± 0.14 GPa and 949 ± 92 °C (stage I), corresponding to crustal depths of ～55 km. Zircon yielded an U–Pb age of 557 ± 16 Ma, inferred to date crystallization of zircon during peak or immediately post‐peak metamorphism. Formation of plagioclase + orthopyroxene‐bearing coronas surrounding garnet indicates a near‐isothermal decompression of the high‐pressure granulites to lower pressure granulite facies conditions (stage II). Development of plagioclase + amphibole‐coronas enclosing the same garnet porphyroblasts shows subsequent cooling into amphibolite facies conditions (stage III). Symplectitic textures of the corona assemblages indicate rapid decompression. The high‐pressure granulite facies metamorphism of the Lurio Belt, followed by near‐isothermal decompression and subsequent cooling, is in accordance with a long‐lived tectonic history accompanied by high magmatic activity in the Lurio Belt during the late Neoproterozoic–early Palaeozoic East‐African–Antarctic orogeny.  相似文献   

15.
赞比西造山带位于非洲中南缘,是新元古代-早古生代泛非造山运动的重要组成部分,形成于冈瓦纳古陆中心陆块缝合期间。赞比西带大地构造位置位于刚果克拉通和卡拉哈里克拉通之间,东连莫桑比克带,北接卢弗里安弧,西部和纳米比亚的达马拉构造带相呼应。带内主要地层单元为基底杂岩和一套沉积在硅铝质基底上的浅变质沉积序列。岩石学及构造学证据证明沉积作用发生在陆内裂谷盆地中,大量同位素年龄限制了盆地演化时代大致为880～820Ma;赞比西带在600～450Ma的泛非造山事件中再次活化,韧性剪切和大范围糜棱岩化导致了角闪岩相变质作用和同构造期花岗质岩体侵入事件同时发生。赞比西带目前已发现的矿产包括岩浆通道型镍硫化物矿床和浅成低温热液型硅锌矿等。笔者通过对赞比西带的地质演化和矿床成矿作用进行系统总结,并将赞比西带内的主要矿床和国内类似矿床进行对比分析,以期为赞比西带找矿实践提供依据或线索。  相似文献   

16.
《地学前缘(英文版)》2019,10(6):2265-2280
We carried out SHRIMP zircon U-Pb dating on A-type granitic intrusions from the Namaqua-Natal Province,South Africa,Sverdrupfjella,western Dronning Maud Land,Antarctica and the Nampula Province of northern Mozambique.Zircon grains in these granitic rocks are typically elongated and oscillatory zoned,suggesting magmatic origins.Zircons from the granitoid intrusions analyzed in this study suggest~1025-1100 Ma ages,which confirm widespread Mesoproterozoic A-type granitic magmatism in the Namaqua-Natal(South Africa),Maud(Antarctica) and Mozambique metamorphic terrains.No older inherited(e.g.,~2500 Ma Achean basement or~1200 Ma island are magmatism in northern Natal)zircon grains were seen.Four plutons from the Natal Belt(Mvoti Pluton,Glendale Pluton,Kwalembe Pluton,Ntimbankulu Pluton) display 1050-1040 Ma ages,whereas the Nthlimbitwa Pluton in northern Natal indicates older 1090-1080 Ma ages.A sample from Sverdrupfjella,Antarctica has~1091 Ma old zircons along with~530 Ma metamorphic rims.Similarly,four samples analysed from the Nampula Province of Mozambique suggest crystallization ages of~1060-1090 Ma but also show significant discordance with two samples showing younger~550 Ma overgrowths.None of the Natal samples show any younger overgrowths.A single sample from southwestern Namaqualand yielded an age of~1033 Ma.Currently available chronological data suggest magmatism took place in the Namaqua-Natal-MaudMozambique(NNMM) belt between~1025 Ma and~1100 Ma with two broad phases between~1060-1020 Ma and 1100-1070 Ma respectively,with peaks at between~1030-1040 Ma and~1070-1090 Ma.The age data from the granitic intrusions from Namaqualand.combined with those from Natal,Antarctica and Mozambique suggest a crude spatial-age relationship with the older1070 Ma ages being largely restricted close to the eastern and western margins of the Kalahari Craton in northern Natal,Mozambique.Namaqualand and WDML Antarctica whereas the younger 1060 Ma ages dominate in southern Natal and western Namaqualand and are largely restricted to the southern and possibly the western margins of the Kalahari Craton.The older ages of magmatism partially overlap with or are marginally younger than the intracratonic Mkondo Large lgneous Provinee intruded into or extruded onto the Kalahari Craton,suggesting a tectonic relationship with the Maud Belt.Similar ages from granitic augen gneisses in Sri Lanka suggest a continuous belt stretching from Namaqualand to Sri Lanka in a reconstituted Gondwana,formed during the terminal stages of amalgamation of Rodinia and predating the East African Orogen.This contiguity contributes to defining the extent of Rodinia-age crustal blocks,subsequently fragmented by the dispersal of Rodinia and Gondwana.  相似文献   

17.
刘晓春 《岩石学报》2009,25(8):1808-1818
东南极普里兹带是一条经受格林维尔期和泛非期高级构造热事件影响的多相变质带,其构造演化过程与罗迪尼亚和冈瓦纳超大陆的形成密切相关.新的岩石学和年代学资料表明,普里兹带中的格林维尔期高级变质作用是区域性的,并经历了>970Ma和930～900Ma两个演化阶段(期),变质条件达到相对高温高压的麻粒岩相.格林维尔期造山作用起始于活动大陆边缘或岛弧环境下的岩浆增生,最后发展到陆陆碰撞,从而使印度、东南极西陆块和非洲的卡拉哈里克拉通拼合在一起,构成了罗迪尼亚超大陆的重要组成部分之一.普里兹带中的泛非期高级变质作用并不象前人认为的那样只发生在中低压麻粒岩相条件下,而是达到高压麻粒岩相,并具有近等温减压的顺时针P-T演化轨迹.格林维尔期变质先驱的普遍存在说明泛非期碰撞造山事件主要叠加在印度-南极陆块东缘的基底杂岩之上,所以其主缝合线的位置应该在现今普里兹带的东南方向,并可能向南极内陆延伸到甘布尔采夫冰下山脉.对不同类型岩石的精细定年揭示,普里兹带中泛非期造山作用过程从570Ma一直持续到490Ma,这与东非造山带的晚期碰撞阶段大致相吻合.因此,冈瓦纳超大陆的最后拼合可能是通过西冈瓦纳、印度-南极陆块和澳大利亚-南极陆块等三个陆块的近于同期碰撞来完成的.  相似文献   

18.
The Southern Prince Charles Mountains (SPCM) are mostly occupied by the Archaean Ruker Terrane. The Lambert Terrane crops out in the northeastern part of the SPCM. New geochemical and zircon U–Pb SHRIMP ages for felsic orthogneisses and granitoids from both terranes are presented. Orthogneisses from the Ruker and Lambert terranes differ significantly in their major and trace-element compositions. Those from the Ruker Terrane comprise two distinct groups: rare Y-depleted and abundant Y-undepleted. U–Pb isotopic data provide evidence for tonalite−trondhjemite emplacement at 3392 ± 9 and 3377 ± 9 Ma, pre-tectonic granite emplacement at 3182 ± 9 Ma, metamorphism(?) at c. 3145 Ma, and thermal events at c. 1300(?) and 626 ± 51 Ma. The Lambert Terrane orthogneisses probably originated in a continental magmatic arc. Zircon dating shows a very different geological history: pre-tectonic granitoid emplacement at 2423 ± 18 Ma, metamorphism at 2065 ± 23 Ma, and syn-tectonic granitoid emplacement at 528 ± 6 Ma, syn-tectonic pegmatite emplacement at 495 ± 18 Ma. The Lambert Terrane can be correlated with neither the Meso- to Neoproterozoic Beaver Terrane in the Northern PCM, which differs in isotopic composition, nor with the Archaean Ruker Terrane, which differs in both granitoid chemical composition and the timing of major geological events. It represents a Palaeoproterozoic orogen which experienced strong tectonic re-activation in Pan-African times. The Lambert Terrane has some geochronological features in common with the Mawson Block, which comprises south Australia and some areas in East Antarctica.  相似文献   

19.
Three single zircon Pb-Pb evaporation dating studies were performed on felsic orthogneisses and migmatites from the Longido and Lossogonoi ruby districts, Mozambique Belt of north-eastern Tanzania, in order to better constrain the geological setting of gemstone mineralizations. Igneous emplacement ages of protoliths ranging between 2636 and 2448 Ma document for the first time the presence of a Neoarchean to Lower Paleoproterozoic (Siderian) basement reworked in the Late Neoproterozoic Mozambique Belt of north-eastern Tanzania. This ancient crust of unknown dimension is well documented farther south, but also in south-eastern Kenya. A shearing event under high-grade amphibolite facies conditions, postdating the Pan-African metamorphic peak at 640 Ma and following nappes emplacement is demonstrated at ca. 610 Ma from metamorphic zircons of Lossogonoi district. In Lossogonoi district, ruby crystallizes during this last stage of deformation.  相似文献   

20.
Granulite-facies rocks are intermittently exposed in a roughly E–W trending belt that extends for approximately 2000 km across the North China Craton, from the Helanshan, Qianlishan, Wulashan–Daqingshan, Guyang and Jining Complexes in the Western Block, through the Huai'an, Hengshan, Xuanhua and Chengde Complexes in the Trans-North China Orogen, to the Jianping (Western Liaoning), Eastern Hebei, Northern Liaoning and Southern Jilin Complexes in the Eastern Block. The belt is generally referred to as the North China Granulite-Facies Belt, previously interpreted as the lowest part of an obliquely exposed crust of the North China Craton. Recent data indicate that the North China Granulite-Facies Belt is not a single terrane. Instead, it represents components of three separate terranes: the Eastern and Western Blocks and Trans-North China Orogen. Each of these units records different metamorphic histories and reflect the complex tectonic evolution of the NCC during the late Archean and Paleoproterozoic. Mafic granulites in the Eastern Block and the Yinshan Terrane (Western Block) underwent medium-pressure granulite-facies metamorphism at about 2.5 Ga, with anticlockwise P–T paths involving near isobaric cooling following peak metamorphism, reflecting an origin related to intrusion and underplating of mantle-derived magmas. Pelitic granulites in the Khondalite Belt (Western Block) underwent medium-pressure granulite-facies metamorphism at about 2.0–1.9 Ga, with clockwise P–T paths, which record the Paleoproterozoic amalgamation of the Yinshan and Ordos Terranes to form the Western Block. Mafic and pelitic granulites in the Trans-North China Orogen experienced high- to medium-pressure granulite-facies metamorphism at 1.85 Ga, with clockwise P–T paths involving nearly isothermal decompression following peak metamorphism, which are in accord with the final collision between the Eastern and Western Blocks to form the North China Craton at 1.8 Ga. The NCGB cannot therefore represent a separate unique terrane; instead it reflects the amalgamation of three separate granulite terranes that evolved independently and at different times.  相似文献   

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