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1.
R Srinivasan K Naha Y J Bhaskar Rao A B Vrevsky S I Rybakov A I Golubev M Efimov 《Journal of Earth System Science》1993,102(4):567-585
The middle to late Archaean rocks of Kola and Karelia in the eastern Baltic shield consist of the Infracomplex overlain by the Saamian complex, and the Lopian greenstone belts. The Infracomplex which forms the basement is a polymigmatite, parts of which are at least 3100 Ma old. The Saamian in the central Belomorian region comprises granite gneiss, amphibolite, garnet-kyanite gneiss and high alumina gneisses which belong to the Keret, Hetolombina and Chupa suites. The Lopian greenstone belts ranging in age from 3000 to 2700 Ma are composed of peridotitic, pyroxenitic and basaltic komatiites, tholeiitic basalts, andesites, dacites and rhyolites, together with tuffs, graywackes and iron formations. Whereas there is a dominance of volcanic over sedimentary rocks in the greenstone belts of the Baltic shield, a significant proportion of detrital and chemogenic sedimentary rocks characterizes the Dharwar succession of approximately the same time span in the southern Indian shield. Association of mature and immature detrital sedimentary rocks with bimodal volcanic assemblages points to a back-arc setting for the Dharwar belts. This contrasts with the association of immature sediments with calc-alkaline volcanic rocks in the greenstone belts of the eastern Baltic shield, suggesting an island arc environment there. 相似文献
2.
华北克拉通北部的怀安杂岩中分布着一些呈团块状、透镜状或似层状产出的含BIF岩石组合.相对于华北克拉通绿岩带,研究区内的含BIF岩石组合具有规模小、岩性复杂多样以及后期叠加强烈的变质-变形改造等特点,其研究程度较低.在野外地质填图的基础上,通过岩石学、同位素年代学、地球化学研究表明:（1）天镇-怀安地区的含BIF岩石组合主要由条带状（含辉石/角闪）磁铁石英岩、变质基性火山岩（二辉麻粒岩/含辉石斜长角闪岩/高压麻粒岩）、石榴黑云斜长片麻岩和少量石榴石英岩条带或团块组成,这些岩石彼此呈夹层或互层状伴生产出;天镇-怀安地区BIF矿体规模小、与变质火山岩密切共生等特征表明其属于Algoma型.（2）条带状（含辉石/角闪）磁铁石英岩中残留的中-基性火成岩锆石年龄（2 489±19 Ma）可代表含BIF岩石组合的形成时代,并经历了1 800~1 850 Ma变质作用叠加改造.（3）含BIF岩石组合中火山岩地球化学特征显示Rb、Ba、U、Pb等元素富集和Nb、Ta等元素亏损,结合微量元素蛛网图和稀土配分模式对比认为其产出构造背景为弧后盆地,铁矿石PAAS标准化稀土配分图解具有明显Eu正异常,表明与海底热液活动密切相关. 相似文献
3.
5.
Hugo de Boorder Maarten J. Zeylmans van Emmichoven Vitaliy A. Privalov 《Ore Geology Reviews》2006,29(3-4):242-259
The East European Platform is underlain by Archaean and Proterozoic complexes of the East European Craton. In the southwest these are locally exposed in the Ukrainian Shield and the Voronezh Massif on either side of the ca. 2000 km long ESE-striking late Palaeozoic Pripyat–Dniepr–Donets rift. Evaluation with Landsat imagery of 1 : 1,000,000 scale published maps of the Precambrian complexes [Zaritsky, A.I., Galetsky, L.S. (Eds.), 1992. Geology and Metallogeny of the Southwest of the East-European Platform Map Series, 1 : 1,000,000, Ukrainian State Committee on Geology and Utilization of Mineral Resources, Kiev.] is largely obstructed by a cover of post-Palaeozoic sediments and soils of variable thickness. This obstruction is aggravated by an almost continuous patchwork of farmlands. However, analysis of the current drainage patterns in the Dniepr River basin and surrounding regions reveals a spatial coincidence of numerous stream courses and watersheds with previously inferred steep, transcrustal discontinuities of most probably Precambrian age.Transcrustal dislocations constituted important pathways for heat and fluids as is indicated by the distribution of a large proportion of assumed Early Proterozoic hydrothermal iron and gold deposits along them. This distribution is underpinned by the spatial coincidence of mineralization and elongate areas of highly irregular magnetization attributed to uneven distribution of hydrothermal magnetite in banded iron formation. In view of the extent of these dislocations, both vertically and laterally, the generation of hydrothermal fluid flow, emplacement of mantle-sourced magma and associated mineral potential away from banded iron formation complexes is likely. A second group of gold deposits, of Archaean age, is known to occur in association with still recognizable volcanic edifices in greenstone complexes. It is not known if and to what extent such Archaean gold deposits are related to these major transcrustal discontinuities. The kinematics and dynamics of these dislocations and pathways appear largely unknown and deserve high-priority investigation. The geological longevity of the transcrustal dislocation framework till the present day inferred from the current drainage systems is corroborated, however, by repeated regional topographical levelling surveys. 相似文献
6.
Archaean gold mineralization in central eastern Brazil: a review 总被引：1，自引：0，他引：1
A. Bernasconi 《Mineralium Deposita》1985,20(4):277-283
7.
The Archaean granite‐greenstone rocks of the Marymia Inlier outcrop within Proterozoic rocks forming the Capricorn Orogen. Five major deformation events are recognised in the rocks of the Plutonic Well and Baumgarten greenstone belts. The first two events were Late Archaean and synchronous with major epithermal gold mineralisation in the belts. Palaeoproterozoic extensional faulting was probably related to the early stages of the Capricorn Orogeny. The fourth event records a compressional phase of the Capricorn Orogeny associated with greenschist‐facies metamorphism, whereas the last major event involved wrench faulting associated with minor folding. The Archaean tectonic history, rock types and timing of mineralisation strongly suggest that the Marymia Inlier is part of the Yilgarn Craton, and that each of the provinces in the craton experienced the same geological history since 2.72 Ga. The inlier is now interpreted to include two components; one is the eastern or northern extension of either the Narryer Terrane, Murchison Province or Southern Cross Province, and the other is the northwestern extension of the Eastern Goldfields Province. The Jenkin Fault, which was active in Proterozoic times, separates these two components. 相似文献
8.
R.D. Gee 《Tectonophysics》1979,58(3-4)
The Western Australian Shield consists of two large Archaean cratons that are partly covered by remnant Proterozoic sedimentary basins and partly surrounded by Proterozoic mobile belts. Archaean terrains are either granitoid-greenstone, or high-grade gneiss, the regional distribution of which influences the style of Proterozoic tectonism.Granitoid-greenstone terrains consist of thick volcanogenic sequences, now occurring as dismembered synclinal keels within voluminous granitoidand display features that are uniquely Archaean. The gneiss terrains, although severely modified and dismembered by metamorphism and plutonism, seem to display a more uniformitarian tectonic style than the granitoid-greenstones.Mounting evidence in the Yilgarn Block suggests that the gneiss terrains represent a pre-greenstone basement, which was probably very extensive, both outside and within the greenstone areas. The most extensive area of gneiss lies in a huge arc around the western part of the Yilgarn Block, creating a novel situation where older rocks seemingly “wrap around” younger rocks. It is postulated that the precursors of the two major granitoidgreenstone terrains were huge, discrete, somewhat rounded volcanic basins that developed within extensive and perhaps continuous crust. At least in the Pilbara, there is a phenomenally continuous volcanic stratigraphy. Despite the basic similarities there are sufficient differences between the two volcanic basins to suggest independent evolution, whereby similar processes operated in different places in different times.These granite—greenstone areas had largely stabilised by about 2500 m.y. and, during the Proterozoic, behaved as cratonic blocks that tended not to participate in the mobile belts. Thus, the Capricorn Orogen developed as an ensialic geosyncline, on gneiss basement, between the two cratons. Where Proterozoic sedimentary basins transgress on to the cratons, they are preserved as gently folded and virtually unmetamorphosed covers. Within the orogenic zone itself, trough sedimentation, prograde metamorphism, basement reworking, multiple deformation and granitoid emplacement were active over the period 2000-1600 m.y. Superimposed on the Capricorn Orogen is the intracratonic Bangemall Basin (about 1100-1000 m.y.) which displays patterns of cratonic deformation that relate closely to the underlying structures.Along the southeastern margin of the Yilgarn Block is the Albany-Fraser Province which developed over an interval from 1900 m.y., or older, to 1100 m.y. Tectonic zonation is expressed by a linear striping of contrasting rocks that become younger away from the Yilgarn Block. Rather than an accretionary origin, voluminous granitoid, basemeni reworkingand absence of geosynclinal sedimentation suggest a discrete zone of high crustal strain and high thermal activity, and the belt is likened to an arrested rift in a continental setting. 相似文献
9.
M.B. Katz 《Precambrian Research》1985,27(4):307-319
The Archaean—Proterozoic crust of many Precambrian terrains consists of two contrasting tectonic units: Archaean cratonic blocks made up of granite—greenstone terrains and Archaean—Proterozoic mobile zones, fold belts and orogens which separate and tend to surround and flow around the cratons. The cratons are relatively rigid blocks, but have a history of ductile and brittle deformations. The surrounding mobile belts are either high-strain, high-grade metamorphic belts or folded basins. Thus, the relatively rigid cratons are surrounded by more ductile zones of mobility. It is speculated that the Archaean cratons are originally separate, although neighbouring ensialic, polygonal miniplate blocks of a single continent which have moved relative to one another according to the mantle controls and the prevailing Eulerian poles, and this mutual jostling has progressively deformed their common boundaries. The deformed boundaries are now the sites of the surrounding ductile and higher strain mobile belts, which are persistent crustal defects, while the cratons represent the more rigid and lower strain cores and relicts, which have stabilized after the Archaean. The mega-scale relationships between the cratons and mobile belts (e.g., East Africa) are compared to the smaller scale micro—meso-scale porphyroclast-matrix structures found in augen gneisses and mylonites. These structural relationships are of vastly different magnitudes (108), but as there exists a continuum on all the intermediate scales they may all be related. Their geometric similarities are interpreted as having a common mechanical—rheological origin. 相似文献
10.
Analysis of 3.3 Ga tonalite–trondhjemite–granodiorite (TTG) series granitoids and greenstone belt assemblages from the Bundelkhand craton in central India reveal that it is a typical Archaean craton. At least two greenstone complexes can be recognized in the Bundelkhand craton, namely the (i) Central Bundelkhand (Babina, Mauranipur belts) and (ii) Southern Bundelkhand (Girar, Madaura belts). The Central Bundelkhand greenstone complex contains three tectonostratigraphic assemblages: (1) metamorphosed basic or metabasic, high-Mg rocks; (2) banded iron formations (BIFs); and (3) felsic volcanics. The first two assemblages are regarded as representing an earlier sequence, which is in tectonic contact with the felsic volcanics. However, the contact between the BIFs and mafic volcanics is also evidently tectonic. Metabasic high-Mg rocks are represented by amphibolites and tremolite-actinolite schists in the Babina greenstone belt and are comparable in composition to tholeiitic basalts-basaltic andesites and komatiites. They are very similar to the metabasic high-Mg rocks of the Mauranipur greenstone belt. Felsic volcanics occur as fine-grained schists with phenocrysts of quartz, albite, and microcline. Felsic volcanics are classified as calc-alkaline dacites, less commonly rhyolites. The chondrite-normalized rare earth element distribution pattern is poorly fractionated (LaN/LuN = 11–16) with a small negative Eu anomaly (Eu/Eu* = 0.68–0.85), being characteristic of volcanics formed in a subduction setting. On Rb – Y + Nb, Nb – Y, Rb – Ta + Yb and Ta – Yb discrimination diagrams, the compositions of the volcanics are also consistent with those of felsic rocks formed in subduction settings. SHRIMP-dating of zircon from the felsic volcanics of the Babina belt of the Central Bundelkhand greenstone complex, performed for the first time, has shown that they were erupted in Neoarchaean time (2542 ± 17 Ma). The early sequence of the Babina belt is correlatable with the rocks of the Mauranipur belt, whose age is tentatively estimated as Mesoarchaean. The Central Bundelkhand greenstone complex consists of two (Meso- and Neoarchaean) sequences, which were formed in subduction settings. 相似文献
11.
12.
Banded iron formations of the Iron Ore Group (Archean greenstone belts) of Jharkhand-Orissa region, India host a good number
of large iron ore deposits (Fe wt %> 62). Iron ore mineralization of Gandhamardan hill is one of them where iron ores occur
in two stratigraphic horizons. One is strictly confined within banded iron formation (stratabound mineralization) with irregular
geometry, and show fracture filling and replacement vein-type mineralization along the fringes of hard massive ores of the
core. This type of mineralization is exposed along the western slope of the hill. Hard massive and laminated ores dominate
this mineralization. The other type occurs as low dipping sheet like body above banded iron formation and covered by laterites
forming the top of the hill. Flaky ores dominate this mineralization with formation of hard goethitic crust near the top.
Both the mineralizations contain mineralized banded iron formation corestones surrounded by hard massive or flaky iron ores.
Hard massive ores are entirely represented by martite-microplaty hematite mineralogy. Hard laminated ores contain microplaty
hematite and few martite grains representing early magnetites of the banded iron formation. Flaky ores are high porosity ores
produced by leaching of silica, martite and microplaty hematite. Hard goethitic ores are developed due to replacement of martite
and microplaty hematite or precipitation of goethite in the pore spaces. 相似文献
13.
《International Geology Review》2012,54(11):1409-1428
ABSTRACTThe Mauranipur and Babina greenstone belts of the Bundelkhand Craton are formed of the Central Bundelkhand greenstone complex (CBGC). This complex represents tectonic collage which has not been previously studied in depth. The purpose of this study is to contribute to the understanding of the main features of the Archaean crustal evolution of the Bundelkhand Craton. The CBGC consists of two assemblages: (1) the early assemblage, which is composed of basic-ultramafic, rhyolitic–dacitic, and banded iron formation units, and (2) the late assemblage, which is a felsic volcanic unit. The units and assemblages are tectonically unified with epidote–quartz–plagioclase metasomatic rocks formed locally in these tectonic zones.The early assemblage of the Mauranipur greenstone belt is estimated at 2810 ± 13 Ma, from the U–Pb dating (SHRIMP, zircon) of the felsic volcanics. Also, there are inherited 3242 ± 65 Ma zircons in this rock. It is deduced that this assemblage is related to early felsic subduction volcanism during the Mesoarchaean that occurred in the Bundelkhand Craton.Zircons extracted from metasomatic rocks in the early assemblage’s high-Mg basalts show a concordant age of 2687 ± 11 Ma. This age is interpreted as a time of metamorphism that occurred simultaneously with an early accretion stage in the evolution of the Mauranipur greenstone belt.The felsic volcanism, appearing as subvolcanic bodies in the late assemblage of the Mauranipur greenstone belt, is estimated to be 2557 ± 33 Ma from the U–Pb dating (SHRIMP, zircon) of the felsic volcanic rocks. This rock also contains inherited 2864 ± 46 Ma zircons. The late assemblage of the Mauranipur greenstone belt corresponds with a geodynamic setting of active subduction along the continental margin during Neoarchaean.The late assemblage Neoarchaean felsic volcanic rocks from the Mauranipur and Babina greenstone belts are comparable in age and geochemical characteristics. The Neoarchaean rocks are more enriched in Sr and Ba and are more depleted in Cr and Ni than the Mesoarchaean felsic volcanic rocks of the early assemblage.Through isotopic dating and the geochemical analysis of the volcanic and metasomatic rocks of the CBGC, this study has revealed two subduction–accretion events, the Meso–Neoarchaean (2.81–2.7 Ga) and Neoarchaean (2.56–2.53 Ga), during the crustal evolution of the Bundelkhand Craton (Indian Shield). 相似文献
14.
A low-strain domain has been identified in the metamorphosed, mostly highly deformed volcanic and sedimentary rocks of the early Archaean Isua supracrustal belt. This domain contains well-preserved volcanic and sedimentary features, including basaltic pillow lavas, pillow breccia, heterogeneous volcanic breccia, amygdules in metabasalt, and polymict conglomerate dominated by recrystallized chert and volcanic clasts. The low-strain domain is bounded by highly deformed rocks mostly derived from basalt, chert, and banded iron formation. These discoveries demonstrate that some primary features have escaped the pervasive metasomatism dominant in other parts of the belt and, furthermore, strengthen the characterization of the Isua supracrustals as a typical greenstone belt. 相似文献
15.
《Ore Geology Reviews》2008,33(3-4):500-510
Archean terrains of the Quadrilátero Ferrífero comprise a greenstone belt association surrounded by granitoid–gneiss complexes, mainly composed of banded TTG gneisses whose igneous protoliths are older than 2900 Ma. This early continental crust was affected by three granitic magmatic episodes during the Neoarchean: ca. 2780 to 2760 Ma; 2720 to 2700 Ma; and 2600 Ma. Dating of felsic volcanic and volcaniclastic rocks defines a felsic magmatic event within the greenstone belt association around 2772 Ma, contemporaneous with emplacement of several of the granitic plutons and constrains a major magmatic and tectonic event in the Quadrilátero Ferrífero. Lead isotopic studies of lode–gold deposits indicate that the main mineralization episode occurred at about 2800 to 2700 Ma.Proterozoic evolution of the Quadrilátero Ferrífero comprises deposition of a continental-margin succession hosting thick, Lake Superior-type banded iron formations, at ca. 2500 to 2400 Ma, followed by deposition of syn-orogenic successions after 2120 Ma. The latter is related to the Transamazonian Orogeny. The western part of the Quadrilátero Ferrífero was also affected by the Brasiliano Orogeny (600 to 560 Ma). 相似文献
16.
Mineralization Ages of the Jiapigou Gold Deposits,Jilin 总被引：1，自引：0，他引：1
Li Junjian Shen Baofeng Mao Debao Li Shuangbao Zhou Huifang Cheng Yuming Tianjin Institute of Geology Mineral Resources Chinese Academy of Geological Sciences Tianjin Nonferrous Metal Geological Exploration Bureau Changchun Jilin 《《地质学报》英文版》1997,71(2):180-188
The Jiapigou gold deposits are typical vein type deposits associated withArchaean greenstone belts in China. According to the crosscutting relationships between dykesand auriferous veins, single hydrothermal zircon U-Pb dating and quartz K-Ar,~(40)Ar-~(39)Ar andRb-Sr datings, the main mineralization stage of the Jiapigou deposit has been determined to be2469-2475 Ma, while mineralization superimposition on the gold deposit occurred in1800-2000 Ma and 130-272 Ma. They form a mineralization framework of one oldermetallogenic epoch (Late Archaean-Early Proterozoic) and one younger metallogenic epoch(Mesozoic) of gold deposits in Archaean greenstone belts in China. 相似文献
17.
Variations in metamorphic grade, structural style, isotopic ages and granite geochemistry observed within the Yilgarn craton, and between the Yilgarn and Pilbara cratons, Western Australia, are interpreted in terms of vertical zonation of the Archaean crust. We correlate the gneiss-granulite suite of the Wheat Belt (southwestern Yilgarn) with concealed coeval infracrustal roots of the low-grade granite—greenstone Kalgoorlie terrain (eastern Yilgarn). Differences between the Pilbara, Southern Cross and Laverton granite—greenstone blocks and the downfaulted linear greenstone belts of the Kalgoorlie block are interpreted in terms of deeper-level exposure in the first three blocks.Ultramafic—mafic volcanic sequences in the Yilgarn craton can be divided into at least two major groups — the lower greenstones, regarded as relicts of a once extensive simatic crust, and the significantly younger upper greenstones, believed to have formed within linear troughs following the intrusion of Na-rich granites.At least three major Archaean granite phases occur in Western Australia: (1) 3.1-2.9 b.y. old (recognized to date only in the western Yilgarn and in the Pilbara craton); (2) 2.8-2.7 b.y. old, and (3) 2.6 b.y. old (the two latter phases can only be separated from each other in the eastern Yilgarn, and phase (3) is also identified in the Pilbara). In the main, granites of phases (1) and (2) are Na-rich and those of phase (3) are K-rich. There is evidence for a secular increase in Rb levels and initial 87Sr/86Sr ratios. It is suggested that the K-rich granites grade down into Na-rich granites, and the former were generated by ensialic anatexis resulting in upward migration of K, Rb, U, and Th-enriched magmas.A review of data from several Archaean cratons in other continents suggests that evidence from these regions can be interpreted in terms of the general model of crustal evolution proposed for Western Australia. Implications of this model concerning petrogenesis of Archaean plutonic and volcanic suites, geothermal gradients and tectonic evolution of greenstone belts are discussed. Partial melting associated with mantle diapirism is thought to have given rise to the ultramafic—mafic volcanic cycles. Widespread subsidence and partial melting of this crust yielded Na-rich acid magmas. The development of the upper greenstones was confined to linear belts in a partly cratonized crustal environment. About 2.6 b.y. ago a rise in the geothermal gradient resulted in regional metamorphism and crusctal anatexis which gave rise to the K-rich granites. 相似文献
18.
The Sr isotopic composition of ‘seawater’, as measured on carbonate rocks, shows a composite pattern during geologic history. All known Archaean data are compatible with contemporaneous upper mantle 87Sr/86Sr values. This is followed by a strong increase in the radiogenic component during the 2.5–2.1 b.y. period, a less pronounced increase during the remaining portion of the Proterozoic and a decrease during the Phanerozoic. The trend closely resembles the K2O/Na2O secular variations in composition of igneous and sedimentary rocks (Engelet al, Bull. Geol. Soc. Amer. 85, 843–858, 1974) and probably reflects the fractionation state of the contemporary crust. The data are compatible with recent suggestions of three major tectonic regimes during geologic history: greenstone belts during the Archaean, mobile belts during the Proterozoic and plate tectonics during the Phanerozoic. They also indicate that continental crust during the Archaean contributed only subordinate Sr into the meteoric cycle. 相似文献
19.
Intense post-depositional alteration has profoundly affected sandstones in the volcanic portions of Early Archaean (3·5–3·3 Ga) greenstone belts. The mineralogy and bulk compositions of most grains have been completely destroyed by pervasive metasomatism, but grain textures are commonly well preserved. Consequently, microtextural information coupled with present alteration compositions as determined petrographically can be used to estimate original framework modes. Silicified Early Archaean volcaniclastic sandstones assigned to the Panorama Formation and Duffer Formation, Warrawoona Group, eastern Pilbara Block, Western Australia, were originally composed of volcanic (VRF) and sedimentary (SRF) rock fragments, volcanic quartz, feldspar, traces of ferromagnesian minerals and pumice. Only volcanic megaquartz remained stable during alteration. All other primary components were replaced by granular microcrystalline quartz (GMC) and sericite. In most areas, the sandstones were composed of dacitic to rhyolitic VRFs, now totally replaced by sericite-poor GMC and recognized by preserved microporphyritic textures. In a few areas, quartz-poor dacitic to andesitic(?) VRFs dominated the detrital assemblage. Minor SRFs and mafic VRFs, now replaced by GMC, are recognized on the basis of colour, internal structures, and internal textures, including skeletal, possible spinifex textures. Detrital feldspar is represented by blocky, sericite-rich grain pseudomorphs. A semi-quantitative point-count scheme, developed for the analysis of heavily altered sandstones, indicates the following primary detrital-mode ranges for Panorama arenites: quartz, 0–28%; feldspar, 0–28%, VRFs, 58–86%, and SRFs 0–25%. In about half the point-counted samples, feldspar could not be distinguished from rock fragments. In such cases, both were counted as one grain type, Lv', which makes up from 84 to 100% of the framework modes of these rocks. These sands were derived from a terrane composed largely of fresh felsic volcanic rocks and sediments, but locally including minor mafic, ultramafic, and sedimentary rocks. Much, but not all, of the felsic volcaniclastic sand represents reworked pyroclastic debris. There is no evidence for contributions from plutonic or metamorphic sources. The Panorama modal assemblage represents a provenance that is lithologically more restricted than that of Archaean greywackes and other siliciclastic units common in the sedimentary portions of these same Early Archaean greenstone belts and younger greenstone belts (3·0–2·7 Ga). 相似文献
20.
A. B. Roy Alfred Kröner Sanjeev Rathore Vivek Laul Ritesh Purohit 《Journal of the Geological Society of India》2012,79(4):323-334
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