Background The Bundelkhand Craton is significant for preserving the multiphase granitoids magmatism from Paleoarchean to Neoarchean periods.It consists of a variety of granite rocks,including TTGs,sanukitoids,and high...Background The Bundelkhand Craton is significant for preserving the multiphase granitoids magmatism from Paleoarchean to Neoarchean periods.It consists of a variety of granite rocks,including TTGs,sanukitoids,and high-K granitoids.This study presents geochemical characteristics of high-silica(68.97 wt.%–73.99 wt.%),low-silica(58.73wt.%–69.94 wt.%),and high K_(2)O(2.77 wt.%–6.16 wt.%)contents of granitoids.Objective The data on Bundelkhand Craton’s granitic magmatism and geodynamics is not sufficiently robust.Geochemical data from this study will be used to further understand the origin,source,and petrogenesis of granitoid rocks and their implications for the evolution of geodynamics.Methodology Twenty-one samples were collected and analyzed for major,trace,and REE elements.Major elements were measured using X-ray fluorescence spectrometry(XRF),and trace and REE elements were analyzed by ICP-MS.Standard procedures from the Geological Survey of India were followed.Results The geochemical analysis presents high-silica(68.97-73.99 wt.%),low-silica(58.73-69.94 wt.%),and high K_(2)O(2.77-6.16 wt.%)contents in granitoids,classified as granite-granodiorite.The rocks are calcic to calcalkalic,magnesian,and range from peraluminous to metaluminous composition.REE patterns showed strong LREE enrichment relative to HREEs,with prominent negative Eu anomalies corresponding to earlier plagioclase fractionation.Multi-element patterns revealed negative anomalies in Nb,Sr,P,and Ti and positive anomalies in Pb.Conclusion The geochemical signatures attributed to the post-collisional magma generation and continental crustal contamination.The studied rocks show A-type and A2-type lineage,suggesting they originated from the melting of continental crust during transitional/post-collisional tectonic activity.The formation of hybrid granitoids in the Bundelkhand Craton is connected to the fractionation of hybrid magmas in shallow-seated magma chambers during these tectonic processes.展开更多
Abstract: The great majority of the Palaeozoic orogenic belts of Central Asia are of the intercontinental type, whose evolution always follows a five-stage model, i.e. the basal continental crust-extensional transitio...Abstract: The great majority of the Palaeozoic orogenic belts of Central Asia are of the intercontinental type, whose evolution always follows a five-stage model, i.e. the basal continental crust-extensional transitional crust-oceanic crust-convergent transitional crust-new continental crust model. The stage for the extensional transitional crust is a pretty long, independent and inevitable phase. The dismembering mechanism of the basal continental crust becoming an extensional continental crust is delineated by the simple shear model put forward by Wernike (1981). The continental margins on the sides of a gently dipping detachment zone and moving along it are asymmetric: one side is of the nonmagmatic type and the other of the magmatic type with a typical bimodal volcanic formation. In the latter case, however, they were often confused with island arcs. This paper discusses the five-stage process of the crustal evolution of some typical orogenic belts in Xinjiang.展开更多
An emerging view is that Earth’s geodynamic regime witnessed a fundamental transition towards plate tectonics around 3.0 Ga(billion years).However,the manifestations of this change may have been diachronous and crato...An emerging view is that Earth’s geodynamic regime witnessed a fundamental transition towards plate tectonics around 3.0 Ga(billion years).However,the manifestations of this change may have been diachronous and craton-specific.展开更多
We present results of field studies for magmatic processes of 2.57-2.52 Ga calc-alkaline plutonic bodies from three corridors in the eastern Dharwar craton(EDC)corresponding to different crustal levels.At deeper level...We present results of field studies for magmatic processes of 2.57-2.52 Ga calc-alkaline plutonic bodies from three corridors in the eastern Dharwar craton(EDC)corresponding to different crustal levels.At deeper levels plutons are bounded by thick zone of migmatites with numerous melt filled shear bands which often overprinted by incipient charnockite.On the other hand in the mid-to-upper crustal levels plutons show relatively sharp contacts and truncates the adjoining basement.The plutons are composite which comprises voluminous intrusive monzodiorite,quartz-monzonite and porphyritic monzogranite in the central part and minor anatectic granites or diatexite at periphery.Numerous xenoliths,Mafic Magmatic Enclaves(MME),disrupted trains of synplutonic mafic dykes are found in both intrusive and anatectic facies.The plutons show magmatic as well as solid-state plastic fabrics defined by magmatic flow banding and C-S fabrics respectively.Crustal scale shear zone network comprising early melt filled NE trending hot ductile dextral shear bands and slightly later colder NW trending sinistral shear bands defined by rotation of mafic boudins,phenocrysts and C-S fabrics.The internal architecture of plutons is attributed to the crustal scale magma chamber processes where voluminous intrusive magmas emplaced into the crust caused reworking of surrounding basement resulting in production of anatectic magmas.Crystallization of voluminous intrusive magmas in the deep crust probably caused development of fractures to mantle depth causing decompression melting of mantle and resultant mafic magmas penetrated the crystallizing host in magma chambers.Field evidences together with published ages and Nd isotope data reveal a spatial link between late Archaean magmatic accretion,reworking and cratonization.展开更多
1 Introduction The North Qinling orogenic belt is characterized by diverse rocks,multi-phase tectonic-magmatic events,which is composed of not only basement rocks of the Qinling Group,but also numerous magmatic rocks in
Continental growth is episodic,and arc-continentalmargin has importance for the formation of continentalcrust in the Shyok Suture Zone(SSZ).To shed light onthe petrogenesis of mantle derived orthogneiss and hybridsour...Continental growth is episodic,and arc-continentalmargin has importance for the formation of continentalcrust in the Shyok Suture Zone(SSZ).To shed light onthe petrogenesis of mantle derived orthogneiss and hybridsource derived leucogranites,a detailed geochemicalstudy has been conducted on granitoids which areexposed between the Shyok-Darbuk of the Pangongtranspressional zone.The Shyok-Darbuk is a complexzone,marked by migmatization,crustal anatexis,in-situemplacement of various granitoids within metapelitesand orthogneiss.Major and trace element data have beenused in this paper to classify the granitoids to estimatethe possible source regions and tectonic environment ofmagma generation and emplacement.展开更多
The Proterozoic felsic and mafic magmatism in India in varied tectonic settings is reviewed and discussed based on available geological,geochemical,and geochronological constraints.Neoarchean-Paleoproterozoic magmatis...The Proterozoic felsic and mafic magmatism in India in varied tectonic settings is reviewed and discussed based on available geological,geochemical,and geochronological constraints.Neoarchean-Paleoproterozoic magmatism,as discrete volcanoplutonic complexes and Large Igneous Provinces(LIPs)in the Bastar,Singhbhum and Dharwar cratons and associated mobile belts are also included.Paleoproterozoic magmatism also contributed to the geodynamics of Himalaya.展开更多
Continental collision zones undergo a series of deep processes,including subduction of oceanic lithosphere,slab rollback,slab breakoff,continental subduction,lithospheric thickening,and lithospheric delamination.How t...Continental collision zones undergo a series of deep processes,including subduction of oceanic lithosphere,slab rollback,slab breakoff,continental subduction,lithospheric thickening,and lithospheric delamination.How these deep processes influence the magma generation and the compositional maturation of continental crust in collision zones remain poorly understood.Based on the consensus that plate motion during the Phanerozoic is primarily driven by the pull force of the subducting oceanic slab,this paper divides the evolution of continental collision zones into four stages,including pre-collision(oceanic subduction),syn-collision,transition,and post-collision,separated,respectively,by initial collision,oceanic slab breakoff,and initial extension occurring at the passive continental margin.Intermediate-felsic magma generated during pre-collision primarily originates from the fractional crystallization of mantle-derived mafic magmas under water-rich conditions,producing a large amount of compositionally complementary hornblende-rich mafic-ultramafic cumulates,whereas intermediate-felsic magma formed during syn-and post-collision is generated primarily by the partial melting of pre-existing hornblende-rich maficultramafic rocks,leaving a large number of eclogitized melting residues.The two-stage process of accumulation and remelting in the collision zone-defined herein as accumelting in this paper-involving the formation of voluminous hornblende-rich cumulates during pre-collision and their remelting during late subduction,syn-collision,and post-collision,has led to the compositional maturation of the continental crust in collision zones.Similar trends in magma compositional changes and deep processes are observed in other collision zones,suggesting that accumelting may be an effective process leading to the generation and compositional maturation of the continental crust.Future research directions should focus on(1)the scarcity of arc magmas and the genesis of intermediate-felsic rocks in continental collision zones,(2)whether eclogitized melting residues or cumulates experienced large-scale delamination or were transferred across the Moho into the seismically-defined upper mantle during syncollision,(3)whether the extensive I-type K-rich intermediate-felsic rocks(including I-type granitic rocks and extrusive equivalents)in the upper plate of collision zones primarily come from the partial melting of pre-existing K-rich mafic-ultramafic meta-igneous rocks(protoliths include cumulates and basaltic rocks)in the lower crust,and(4)whether the lower crust of magmatic arcs containing hornblende-rich cumulates is an important reservoir for volatiles.展开更多
The zircon U-Pb chronology database provides a good opportunity to obtain important zircon growth peak periods in the Earth’s history so as to study the origin and evolution of the crust.It should be noted that resea...The zircon U-Pb chronology database provides a good opportunity to obtain important zircon growth peak periods in the Earth’s history so as to study the origin and evolution of the crust.It should be noted that research preference affects the objectivity of zircon sampling,leading to hot data in the database and age statistics.To evaluate the influence of hot data on statistical results,the W and Y indexes are introduced.Using a Gaussian model of multipeak fitting of zircon U-Pb age frequencies,we identify seven major growth peaks in zircons from the Chinese continental crust,which are 2498.95,1855.82,828.88,444.29,249.46,131.96,and 58.21 Ma.Due to differences in the time scales of zircon growth peaks,these peaks can be divided into two categories:first-order zircon growth peaks(Ⅰ)and second-order zircon growth peaks(Ⅱ),which represent longer and shorter time scales,perhaps due to different kinds of geological dynamics,respectively.In addition,there are clear correspondences between these ages and various geological events recognized by most scholars,namely,the Wutai orogeny,Lvliang orogeny,Jinning orogeny,Caledonian orogeny,Indosinian orogeny,Yanshanian orogeny,and Himalayan orogeny,respectively.展开更多
The Arabian-Nubian Shield(ANS)serves as a key geological archive,preserving the tectono-thermal evolution associated with the Rodinia breakup(∼900–800 Ma)and Gondwana formation(∼800–620 Ma).The Katherina Ring Comp...The Arabian-Nubian Shield(ANS)serves as a key geological archive,preserving the tectono-thermal evolution associated with the Rodinia breakup(∼900–800 Ma)and Gondwana formation(∼800–620 Ma).The Katherina Ring Complex(KRC),located in the Sinai Peninsula,Egypt(northern ANS),exemplifies continental growth through multistage magmatism and orogenesis,spanning the Tonian to Ediacaran periods(∼900–530 Ma).Despite its importance,debates persist regarding the nature,age,crustal characteristics,and magma source evolution of its constituent units.Situated in the northwestern part of the KRC,the Wadi Rofaiyed Cu deposit offers an exceptional natural laboratory for investigating continental crust formation during this interval,owing to its superb exposure and preservation.This study integrates detailed fieldwork,petrographic analyses,whole-rock geochemistry,Sr-Nd isotopes,and in situ zircon U-Pb-Lu-Hf isotopic data.It aims to(i)establish a robust chronological framework for the unmetamorphosed plutonic rocks of the KRC,(ii)advance the understanding of associated geodynamic processes,and(iii)elucidate the episodic magmatism events.The findings show that Wadi Rofaiyed juvenile crust developed in four main phases:(i)a subduction-accretionary phase(∼755 Ma)characterized by intense calc-alkaline magmatism,originating from the partial melting of mafic lower crust;(ii)a syn-collisional phase(∼630 Ma)occurred during the collision between the Saharan metacraton and the younger ANS crust,producing I-type granitoids formed through magma mixing and crustal anatexis;(iii)a post-collisional phase characterized by intermediate I-type(∼595 Ma)to felsic A-type alkaline magma(∼594 Ma),originated from the partial melting of the overthickened lower crust corresponding to lithospheric delamination;and(iv)an anorogenic phase(∼530 Ma)related to the final amalgamation of Greater Gondwana.Isotopic analyses across all four magmatic phases reveal low initial^(87)Sr/^(86)Sr(0.702648–0.703311)and positiveε_(Hf)(t)(+2.84 to+7.78)andε_(Nd)(t)(+2.61 to+5.21)values,consistent with lower crustal sources with depleted mantle-like signatures.The model ages(T_(DM2))for these magmatic rocks derived from zircon Hf(1.2–1.5 Ga)and whole-rock Nd isotopes(0.96–1.17 Ga)support a predominantly juvenile crustal origin.These findings underscore the multistage tectono-magmatic evolution of the northern ANS,advancing our understanding of obduction-accretion dynamics and crustal development during the Neoproterozoic.展开更多
This paper summarizes the new results on the petrogenesis of Mesozoic granitoids and volcanic rocks in South China. The authors propose that these rocks were formed in time and space as a response to regional tectonic...This paper summarizes the new results on the petrogenesis of Mesozoic granitoids and volcanic rocks in South China. The authors propose that these rocks were formed in time and space as a response to regional tectonic regime change from the continent-continent collision of the Indosinian orogeny within the broad Tethyan orogenic domain in the Early Mesozoic （T1-T3） （Period Ⅰ） to the largely extensional setting as a result of the Yanshanian orogeny genetically associated with the NW-WNW-ward subduction of the paleo-Pacific oceanic lithosphere in the Late Mesozoic （J2-K2） （Period Ⅱ）. Of the Period I Indosinian granitoids, the early （T1-T2^1） ones are syn-collisional, and formed in a compressional setting; the late （T2^2-T3） ones are latecollisional, and formed in a locally extensional environment. During the Period Ⅱ Yanshanian magmatism, the Early Yanshanian （J2-J3） granitoid-volcanic rocks, which are distributed mainly in the Nanling Range and in the interior of the South China tectonic block （SCB）, are characteristic of rift-type intraplate magmatism, whereas the Late Yanshanian K1 granitoidovolcanic rocks are interpreted as genetically representing active continental margin magmatism. The K2 tholeiitic basalts interlayered with red beds are interpreted as genetically associated with the development of back-arc extensional basins in the interior of the SCB. The Yanshanian granitoid-volcanic rocks are distributed widely in South China, reflecting extensional tectonics within much of the SCB. The extension-induced deep crustal melting and underplating of mantle-derived basaltic melts are suggested as the two principal driving mechanisms for the Yanshanian granitic magmatism in South China.展开更多
South China as an amalgamation of the Yangtze and Cathaysia blocks is composed of Archean to Mesoproterozoic basement overlain by Neoproterozoic and younger cover.Both the constituent Yangtze and Cathaysia blocks cont...South China as an amalgamation of the Yangtze and Cathaysia blocks is composed of Archean to Mesoproterozoic basement overlain by Neoproterozoic and younger cover.Both the constituent Yangtze and Cathaysia blocks contain well-preserved Neoproterozoic rocks that have been extensively studied in terms of the age and tectonic nature,but less is known about their earlier crustal history due to the incomplete rock record.Recent efforts in investigating the yet survived crustal nature based on isotopic and elemental signatures preserved in igneous and sedimentary rocks have steadily improved our knowledge about the pre-Neoproterozoic continental crustal evolution in South China.In this paper,we summarize the up-to-date pre-Neoproterozoic records,including petrological,geochronological,geochemical and geophysical data,across South China,and discuss its spatiotemporal patterns of the pre-Neoproterozoic crust and the relevant tectonic events.While the xenocrystic/inherited and detrital zircon records suggest widespread Archean(mainly ca.2.5 Ga)crustal components within both the Yangtze and Cathaysia blocks,exposed Archean rocks are only limited to isolated crustal provinces in the Yangtze Block.These Archean rocks are dominated by TTGs(tonalite-trondhjemitegranodiorite)with varied ages(3.3-2.5 Ga)and zircon Hf isotopes,indicating a compositionally heterogeneous nature of the Archean Yangtze Block and,by inference,the development of multiple ancient terranes.The early Paleoproterozoic(2.4-2.2 Ga)tectonomagmatic events characterize the western Yangtze Block and are supportive of an east-west subdivision of the Yangtze basement,whereas the late Paleoproterozoic(2.1-1.7 Ga)orogeneses may have affected a larger area covering both the western and eastern parts of the Yangtze Block,and also the Cathaysia Block.The eastern Yangtze Block with generally northeastward-younging late Paleoproterozoic magmatism and metamorphism likely experienced a prolonged 2.05-1.75 Ga orogenic process welding the various Archean proto-continents,consistent with the documentation of a buried late Paleoproterozoic orogenic belt imaged by deep seismic profiling from its central part and of a slightly older ophiolitic mélange in the northern part.The Cathaysia Block was probably involved in a short-lived 1.9-1.8 Ga orogenic event.The two orogeneses overlapped in time and may have contributed to the cratonization of a possible unified South China,and are referred to be linked with the assembly of the Nuna Supercontinent.The subsequent late Paleoproterozoic to early Mesoproterozoic rift successions and intrusions(1.7-1.5 Ga)in the southwestern Yangtze Block,and the ca.1.43 Ga rifting in Hainan Island of the Cathaysia Block could be responses to the Nuna break-up.Late Mesoproterozoic(1.2-1.0 Ga)magmatism of varied age and nature in different localities of the Yangtze Block is reflective of a complex tectonic process in the context of the assembly of the Rodinia Supercontinent.Similar-aged metamorphism(1.3-1.0 Ga)is recorded in Hainan Island,reflecting the Grenvillian continental collision during the Rodinia assembly,but further studies are necessar y to better constrain the late Mesoproterozoic tectonic framework of South China.展开更多
The Pilbara region of Western Australia is one of only two areas on Earth–the other being the Kaapvaal Craton of southern Africa–that contain well preserved,nearcontinuous geological records of crustal evolution fro...The Pilbara region of Western Australia is one of only two areas on Earth–the other being the Kaapvaal Craton of southern Africa–that contain well preserved,nearcontinuous geological records of crustal evolution from the Paleoarchean into the late Paleoproterozoic.The Pilbara is famous for hosting fossil evidence of early life(stromatolites and microfossils),and for containing a record of the early Archean atmosphere.The geological record extends from granite–greenstone terranes and overlying clastic basins of the 3.53–2.83 Ga Pilbara Craton,across a major unconformity,to a series of 2.78–1.79 Ga volcanic and sedimentary successions.Between 3.53–3.23 Ga,a succession of mantle plume events formed a thick volcanic plateau on older continental crust,remnants of which include enclaves of c.3.6 Ga granitic gneiss and abundant 3.8–3.6 Ga inherited and detrital zircons.During each of the plume events,the volcanic plateau was intruded by crustally-derived granitic rocks,leading to vertical deformation by partial convective overturn.By 3.23 Ga,these processes had established thick continental crust that was then rifted into three microplates separated by c.3.2 Ga basins of oceanic crust.Subsequent plate tectonic processes to 2.90 Ga included subduction,terrane accretion,and orogeny.From 2.78–2.63 Ga the northern Pilbara Craton was affected by minor rifting,followed by deposition of thick basaltic formations separated by felsic volcanic and sedimentary rocks(Fortescue Basin).Rifting in the southern Pilbara resulted in progressively deepening marginal basin sedimentation,including thick units of banded iron formation(Hamersley Basin:2.63–2.45 Ga).展开更多
The Archean Eon was a time of geodynamic changes.Direct evidence of these transitions come from igneous/metaigneous rocks,which dominate cratonic segments worldwide.New data for granitoids from an Archean basement inl...The Archean Eon was a time of geodynamic changes.Direct evidence of these transitions come from igneous/metaigneous rocks,which dominate cratonic segments worldwide.New data for granitoids from an Archean basement inlier related to the Southern S?o Francisco Craton(SSFC),are integrated with geochronological,isotopic and geochemical data on Archean granitoids from the SSFC.The rocks are divided into three main geochemical groups with different ages:(1)TTG(3.02–2.77 Ga);(2)mediumto high-K granitoids(2.85–2.72 Ga);and(3)A-type granites(2.7–2.6 Ga).The juvenile to chondritic(Hf-Nd isotopes)TTG were divided into two sub-groups,TTG 1(low-HREE)and 2(high-HREE),derived from partial melting of metamafic rocks similar to those from adjacent greenstone belts.The compositional diversity within the TTG is attributed to different pressures during partial melting,supported by a positive correlation of Dy/Yb and Sr/Zr,and batch melting calculations.The proposed TTG sources are geochemically similar to basaltic rocks from modern island-arcs,indicating the presence of subduction processes concomitant with TTG emplacement.From~2.85 Ga to 2.70 Ga,the dominant rocks were K-rich granitoids.These are modeled as crustal melts of TTG,during regional metamorphism indicative of crustal thickening.Their compositional diversity is linked to:(i)differences in source composition;(ii)distinct melt fractions during partial melting;and(iii)different residual mineralogies reflecting varying P–T conditions.Post-collisional(~2.7–2.6 Ga)A-type granites reflect rifting in that they were closely followed by extension-related dyke swarms,and they are interpreted as differentiation or partial melting products of magmas derived from subduction-modified mantle.The sequence of granitoid emplacement indicates subduction-related magmatism was followed by crustal thickening,regional metamorphism and crustal melting,and post-collisional extension,similar to that seen in younger Wilson Cycles.It is compelling evidence that plate tectonics was active in this segment of Brazil from~3 Ga.展开更多
Results of a geochemical and geochronological study of the Paleoproterozoic rock assemblage in the Haisyn block of the Ros-Tikych Domain of the Ukrainian Shield are reported.Within the block,the Haisyn Complex compris...Results of a geochemical and geochronological study of the Paleoproterozoic rock assemblage in the Haisyn block of the Ros-Tikych Domain of the Ukrainian Shield are reported.Within the block,the Haisyn Complex comprises granitoids,including pyroxene-bearing diorites,quartz diorites,granodiorites,amphibole-biotite and biotite granites,and aplite and pegmatite granites.Monazite U-Pb isotope age of charnockitic syenite belonging to the Haisyn Complex was defined at 2027±6 Ma.This age coeval with the time of granulite facies metamorphism and emplacement of numerous granitic intrusions in the area.The Sm–Nd apatite isochron yielded an age of 2100±150 Ma.TheεNd isochron value of-5 indicates a long crustal residence time of the crustal protolith.Geochemical data do not indicate any enrichment of the studied rocks in relation to the Eoarchean and Neoarchean charnockites developed in the same area.So,if the model of partial melting of the older crustal protolith is involved then the degree of melting must be quite high.However,deep negative anomalies of Sr,Eu,Zr,and Ti indicate that plagioclase,zircon,and Fe–Ti oxides probably remained unmelted in the source.The Haisyn block was buried in the lower crust at high temperature and pressure conditions in the Paleoproterozoic time.Such a situation resulted in partial melting of the existing crust and formation of melts,containing undigested zircon and bearing ancient Nd isotope signature.展开更多
Having analysised the data collected by our survey ship'Ocean IV 'in the Bransfield Strait in 1991,we recognized that the geomorphology,gravity and magnetic anomalies trending NE direction along bandings. The ...Having analysised the data collected by our survey ship'Ocean IV 'in the Bransfield Strait in 1991,we recognized that the geomorphology,gravity and magnetic anomalies trending NE direction along bandings. The sediments in the Bransfield Strait can be subdivided into two sequences:the first rifting equence and the second rifting sequence.The basement was faulted into a half-graben in northwestern side of the Bransfield trough. Considering the crustal structure crossing the South Shetland Islands,the Bransfield Strait and the Antarctic Peninsula, we propse a two-phase rifting tectonic evolution model and a layered-shear model for the lithospheric deformation under the effects of extensional stress field.展开更多
The Lützow-Holm Complex(LHC) of East Antarctica has been regarded as a collage of Neoarchean(ca.2.5 Ga), Paleoproterozoic(ca. 1.8 Ga), and Neoproterozoic(ca. 1.0 Ga) magmatic arcs which were amalgamated through t...The Lützow-Holm Complex(LHC) of East Antarctica has been regarded as a collage of Neoarchean(ca.2.5 Ga), Paleoproterozoic(ca. 1.8 Ga), and Neoproterozoic(ca. 1.0 Ga) magmatic arcs which were amalgamated through the latest Neoproterozoic collisional events during the assembly of Gondwana supercontinent. Here, we report new geochronological data on detrital zircons in metasediments associated with the magmatic rocks from the LHC, and compare the age spectra with those in the adjacent terranes for evaluating the tectonic correlation of East Antarctica and Sri Lanka. Cores of detrital zircon grains with high Th/U ratio in eight metasediment samples can be subdivided into two dominant groups:(1) late Meso-to Neoproterozoic(1.1-0.63 Ga) zircons from the northeastern part of the LHC in Prince Olav Coast and northern Soya Coast areas, and(2) dominantly Neoarchean to Paleoproterozoic(2.8-2.4 Ga) zircons from the southwestern part of the LHC in southern Lutzow-Holm Bay area. The ca.1.0 Ga and ca. 2.5 Ga magmatic suites in the LHC could be proximal provenances of the detrital zircons in the northeastern and southwestern LHC, respectively. Subordinate middle to late Mesoproterozoic(1.3-1.2 Ga) detrital zircons obtained from Akarui Point and Langhovde could have been derived from adjacent Gondwana fragments(e.g., Rayner Complex, Eastern Ghats Belt). Meso-to Neoproterozoic domains such as Vijayan and Wanni Complexes of Sri Lanka, the southern Madurai Block of southern India, and the central-western Madagascar could be alternative distal sources of the late Meso-to Neoproterozoic zircons. Paleo-to Mesoarchean domains in India, Africa, and Antarctica might also be distal sources for the minor ~2.8 Ga detrital zircons from Skallevikshalsen. The detrital zircons from the Highland Complex of Sri Lanka show similar Neoarchean to Paleoproterozoic(ca. 2.5 Ga) and Neoproterozoic(ca. 1.0 Ga) ages, which are comparable with those of the LHC, suggesting that the two complexes might have formed under similar tectonic regimes. We consider that the Highland Complex and metasedimentary unit of the LHC formed a unified latest Neoproterozoic suture zone with a large block of northern LH-Vijayan Complex caught up as remnant of the ca. 1.0 Ga magmatic arc.展开更多
A diverse suite of Archaean gneisses at Huangbaiyu village in the North China Craton, includes rare fuchsite-bearing （Cr-muscovite） siliceous rocks - known as the Caozhuang quartzite. The Caozhuang quartzite is stro...A diverse suite of Archaean gneisses at Huangbaiyu village in the North China Craton, includes rare fuchsite-bearing （Cr-muscovite） siliceous rocks - known as the Caozhuang quartzite. The Caozhuang quartzite is strongly deformed and locally mylonitic, with silica penetration and pegmatite veining common. It contains abundant 3880-3600 Ma and some Palaeoarchaean zircons. Because of its siliceous nature, the presence of fuchsite and its complex zircon age distribution, it has until now been accepted as a （mature） quartzite. However, the Caozhuang quartzite sample studied here is feldspathic. The shape and cathodoluminescence petrography of the Caozhuang quartzite zircons show they resemble those found in immature detrital sedimentary rocks of local provenance or in Eoarchaean polyphase orthog- neisses, and not those in mature quartzites. The Caozhuang quartzite intra-zircon mineral inclusions are dominated by quartz,展开更多
In this study, we report U–Pb and Lu–Hf isotopic data for zircons from the Mesozoic sandstones of the Upper Yangtze area, which provide critical constraints on the provenance of these sediments and further shed ligh...In this study, we report U–Pb and Lu–Hf isotopic data for zircons from the Mesozoic sandstones of the Upper Yangtze area, which provide critical constraints on the provenance of these sediments and further shed light on the crustal evolution of the Upper Yangtze block. The results of isotopic chronology indicate the following：（1） The provenances of the study area are very complex, and the tectonic evolution process is relatively closed.（2） The provenances are mainly Archean–Proterozoic crystalline basement or recycled material; Paleoproterozoic crustal accretion in the western margin of the Yangtze block and Neoproterozoic magmatic activities related to subduction of the western margin of the Yangtze block; early Cambrian oceanic magmatic activity, which resulted from the intraplate extension of the northern margin of the Yangtze block; late Ordovician–early Silurian magmatic activity in the northern Yangtze block and Hercynian–Indochina uplift and erosion during the Hercynian movement.（3） The Yangtze crustal growth is episodic, and an increasing amount of ancient recycled material became part of the magmatic activity, as the zircon U–Pb ages are relatively young.展开更多
基金Geological Survey of India,Northern Region have provided the financial funding for the study.
文摘Background The Bundelkhand Craton is significant for preserving the multiphase granitoids magmatism from Paleoarchean to Neoarchean periods.It consists of a variety of granite rocks,including TTGs,sanukitoids,and high-K granitoids.This study presents geochemical characteristics of high-silica(68.97 wt.%–73.99 wt.%),low-silica(58.73wt.%–69.94 wt.%),and high K_(2)O(2.77 wt.%–6.16 wt.%)contents of granitoids.Objective The data on Bundelkhand Craton’s granitic magmatism and geodynamics is not sufficiently robust.Geochemical data from this study will be used to further understand the origin,source,and petrogenesis of granitoid rocks and their implications for the evolution of geodynamics.Methodology Twenty-one samples were collected and analyzed for major,trace,and REE elements.Major elements were measured using X-ray fluorescence spectrometry(XRF),and trace and REE elements were analyzed by ICP-MS.Standard procedures from the Geological Survey of India were followed.Results The geochemical analysis presents high-silica(68.97-73.99 wt.%),low-silica(58.73-69.94 wt.%),and high K_(2)O(2.77-6.16 wt.%)contents in granitoids,classified as granite-granodiorite.The rocks are calcic to calcalkalic,magnesian,and range from peraluminous to metaluminous composition.REE patterns showed strong LREE enrichment relative to HREEs,with prominent negative Eu anomalies corresponding to earlier plagioclase fractionation.Multi-element patterns revealed negative anomalies in Nb,Sr,P,and Ti and positive anomalies in Pb.Conclusion The geochemical signatures attributed to the post-collisional magma generation and continental crustal contamination.The studied rocks show A-type and A2-type lineage,suggesting they originated from the melting of continental crust during transitional/post-collisional tectonic activity.The formation of hybrid granitoids in the Bundelkhand Craton is connected to the fractionation of hybrid magmas in shallow-seated magma chambers during these tectonic processes.
文摘Abstract: The great majority of the Palaeozoic orogenic belts of Central Asia are of the intercontinental type, whose evolution always follows a five-stage model, i.e. the basal continental crust-extensional transitional crust-oceanic crust-convergent transitional crust-new continental crust model. The stage for the extensional transitional crust is a pretty long, independent and inevitable phase. The dismembering mechanism of the basal continental crust becoming an extensional continental crust is delineated by the simple shear model put forward by Wernike (1981). The continental margins on the sides of a gently dipping detachment zone and moving along it are asymmetric: one side is of the nonmagmatic type and the other of the magmatic type with a typical bimodal volcanic formation. In the latter case, however, they were often confused with island arcs. This paper discusses the five-stage process of the crustal evolution of some typical orogenic belts in Xinjiang.
基金support from projects:CSIR-GeoMet(No.MLP-0002-FBR-2-EVB)Ministry of Earth Sciences(No.MoES P.O.(Geo)/99(i)/2017).
文摘An emerging view is that Earth’s geodynamic regime witnessed a fundamental transition towards plate tectonics around 3.0 Ga(billion years).However,the manifestations of this change may have been diachronous and craton-specific.
基金funded by Department of Science and Technology(DST),Govt.of India funded project ESS/16/297/2007.
文摘We present results of field studies for magmatic processes of 2.57-2.52 Ga calc-alkaline plutonic bodies from three corridors in the eastern Dharwar craton(EDC)corresponding to different crustal levels.At deeper levels plutons are bounded by thick zone of migmatites with numerous melt filled shear bands which often overprinted by incipient charnockite.On the other hand in the mid-to-upper crustal levels plutons show relatively sharp contacts and truncates the adjoining basement.The plutons are composite which comprises voluminous intrusive monzodiorite,quartz-monzonite and porphyritic monzogranite in the central part and minor anatectic granites or diatexite at periphery.Numerous xenoliths,Mafic Magmatic Enclaves(MME),disrupted trains of synplutonic mafic dykes are found in both intrusive and anatectic facies.The plutons show magmatic as well as solid-state plastic fabrics defined by magmatic flow banding and C-S fabrics respectively.Crustal scale shear zone network comprising early melt filled NE trending hot ductile dextral shear bands and slightly later colder NW trending sinistral shear bands defined by rotation of mafic boudins,phenocrysts and C-S fabrics.The internal architecture of plutons is attributed to the crustal scale magma chamber processes where voluminous intrusive magmas emplaced into the crust caused reworking of surrounding basement resulting in production of anatectic magmas.Crystallization of voluminous intrusive magmas in the deep crust probably caused development of fractures to mantle depth causing decompression melting of mantle and resultant mafic magmas penetrated the crystallizing host in magma chambers.Field evidences together with published ages and Nd isotope data reveal a spatial link between late Archaean magmatic accretion,reworking and cratonization.
基金financially supported by National Natural Science Foundation of China (41372072)Natural Science Foundation of Education Department of Anhui province (KJ2016A025)+1 种基金Dr. Startup Foundation, Anhui university (J10113190090)the State Key Laboratory of Geodynamics, Northwest University
文摘1 Introduction The North Qinling orogenic belt is characterized by diverse rocks,multi-phase tectonic-magmatic events,which is composed of not only basement rocks of the Qinling Group,but also numerous magmatic rocks in
文摘Continental growth is episodic,and arc-continentalmargin has importance for the formation of continentalcrust in the Shyok Suture Zone(SSZ).To shed light onthe petrogenesis of mantle derived orthogneiss and hybridsource derived leucogranites,a detailed geochemicalstudy has been conducted on granitoids which areexposed between the Shyok-Darbuk of the Pangongtranspressional zone.The Shyok-Darbuk is a complexzone,marked by migmatization,crustal anatexis,in-situemplacement of various granitoids within metapelitesand orthogneiss.Major and trace element data have beenused in this paper to classify the granitoids to estimatethe possible source regions and tectonic environment ofmagma generation and emplacement.
文摘The Proterozoic felsic and mafic magmatism in India in varied tectonic settings is reviewed and discussed based on available geological,geochemical,and geochronological constraints.Neoarchean-Paleoproterozoic magmatism,as discrete volcanoplutonic complexes and Large Igneous Provinces(LIPs)in the Bastar,Singhbhum and Dharwar cratons and associated mobile belts are also included.Paleoproterozoic magmatism also contributed to the geodynamics of Himalaya.
基金supported by the National Natural Science Foundation of China(Grant Nos.42121002,42330307,42372079,91755207)the 111 Project(Grant No.B18048)。
文摘Continental collision zones undergo a series of deep processes,including subduction of oceanic lithosphere,slab rollback,slab breakoff,continental subduction,lithospheric thickening,and lithospheric delamination.How these deep processes influence the magma generation and the compositional maturation of continental crust in collision zones remain poorly understood.Based on the consensus that plate motion during the Phanerozoic is primarily driven by the pull force of the subducting oceanic slab,this paper divides the evolution of continental collision zones into four stages,including pre-collision(oceanic subduction),syn-collision,transition,and post-collision,separated,respectively,by initial collision,oceanic slab breakoff,and initial extension occurring at the passive continental margin.Intermediate-felsic magma generated during pre-collision primarily originates from the fractional crystallization of mantle-derived mafic magmas under water-rich conditions,producing a large amount of compositionally complementary hornblende-rich mafic-ultramafic cumulates,whereas intermediate-felsic magma formed during syn-and post-collision is generated primarily by the partial melting of pre-existing hornblende-rich maficultramafic rocks,leaving a large number of eclogitized melting residues.The two-stage process of accumulation and remelting in the collision zone-defined herein as accumelting in this paper-involving the formation of voluminous hornblende-rich cumulates during pre-collision and their remelting during late subduction,syn-collision,and post-collision,has led to the compositional maturation of the continental crust in collision zones.Similar trends in magma compositional changes and deep processes are observed in other collision zones,suggesting that accumelting may be an effective process leading to the generation and compositional maturation of the continental crust.Future research directions should focus on(1)the scarcity of arc magmas and the genesis of intermediate-felsic rocks in continental collision zones,(2)whether eclogitized melting residues or cumulates experienced large-scale delamination or were transferred across the Moho into the seismically-defined upper mantle during syncollision,(3)whether the extensive I-type K-rich intermediate-felsic rocks(including I-type granitic rocks and extrusive equivalents)in the upper plate of collision zones primarily come from the partial melting of pre-existing K-rich mafic-ultramafic meta-igneous rocks(protoliths include cumulates and basaltic rocks)in the lower crust,and(4)whether the lower crust of magmatic arcs containing hornblende-rich cumulates is an important reservoir for volatiles.
基金supported by the National Key R&D Program of China,focused special funding[grant number 2017YFC0601203].
文摘The zircon U-Pb chronology database provides a good opportunity to obtain important zircon growth peak periods in the Earth’s history so as to study the origin and evolution of the crust.It should be noted that research preference affects the objectivity of zircon sampling,leading to hot data in the database and age statistics.To evaluate the influence of hot data on statistical results,the W and Y indexes are introduced.Using a Gaussian model of multipeak fitting of zircon U-Pb age frequencies,we identify seven major growth peaks in zircons from the Chinese continental crust,which are 2498.95,1855.82,828.88,444.29,249.46,131.96,and 58.21 Ma.Due to differences in the time scales of zircon growth peaks,these peaks can be divided into two categories:first-order zircon growth peaks(Ⅰ)and second-order zircon growth peaks(Ⅱ),which represent longer and shorter time scales,perhaps due to different kinds of geological dynamics,respectively.In addition,there are clear correspondences between these ages and various geological events recognized by most scholars,namely,the Wutai orogeny,Lvliang orogeny,Jinning orogeny,Caledonian orogeny,Indosinian orogeny,Yanshanian orogeny,and Himalayan orogeny,respectively.
基金supported by the National Natural Science Foundation of China(No.92162103)the Natural Science Foundation of Hunan Province(No.2022JJ30699,No.2023JJ10064)the Science and Technology Innovation Program of Hunan Province(No.2021RC4055,No.2022RC1182).
文摘The Arabian-Nubian Shield(ANS)serves as a key geological archive,preserving the tectono-thermal evolution associated with the Rodinia breakup(∼900–800 Ma)and Gondwana formation(∼800–620 Ma).The Katherina Ring Complex(KRC),located in the Sinai Peninsula,Egypt(northern ANS),exemplifies continental growth through multistage magmatism and orogenesis,spanning the Tonian to Ediacaran periods(∼900–530 Ma).Despite its importance,debates persist regarding the nature,age,crustal characteristics,and magma source evolution of its constituent units.Situated in the northwestern part of the KRC,the Wadi Rofaiyed Cu deposit offers an exceptional natural laboratory for investigating continental crust formation during this interval,owing to its superb exposure and preservation.This study integrates detailed fieldwork,petrographic analyses,whole-rock geochemistry,Sr-Nd isotopes,and in situ zircon U-Pb-Lu-Hf isotopic data.It aims to(i)establish a robust chronological framework for the unmetamorphosed plutonic rocks of the KRC,(ii)advance the understanding of associated geodynamic processes,and(iii)elucidate the episodic magmatism events.The findings show that Wadi Rofaiyed juvenile crust developed in four main phases:(i)a subduction-accretionary phase(∼755 Ma)characterized by intense calc-alkaline magmatism,originating from the partial melting of mafic lower crust;(ii)a syn-collisional phase(∼630 Ma)occurred during the collision between the Saharan metacraton and the younger ANS crust,producing I-type granitoids formed through magma mixing and crustal anatexis;(iii)a post-collisional phase characterized by intermediate I-type(∼595 Ma)to felsic A-type alkaline magma(∼594 Ma),originated from the partial melting of the overthickened lower crust corresponding to lithospheric delamination;and(iv)an anorogenic phase(∼530 Ma)related to the final amalgamation of Greater Gondwana.Isotopic analyses across all four magmatic phases reveal low initial^(87)Sr/^(86)Sr(0.702648–0.703311)and positiveε_(Hf)(t)(+2.84 to+7.78)andε_(Nd)(t)(+2.61 to+5.21)values,consistent with lower crustal sources with depleted mantle-like signatures.The model ages(T_(DM2))for these magmatic rocks derived from zircon Hf(1.2–1.5 Ga)and whole-rock Nd isotopes(0.96–1.17 Ga)support a predominantly juvenile crustal origin.These findings underscore the multistage tectono-magmatic evolution of the northern ANS,advancing our understanding of obduction-accretion dynamics and crustal development during the Neoproterozoic.
文摘This paper summarizes the new results on the petrogenesis of Mesozoic granitoids and volcanic rocks in South China. The authors propose that these rocks were formed in time and space as a response to regional tectonic regime change from the continent-continent collision of the Indosinian orogeny within the broad Tethyan orogenic domain in the Early Mesozoic （T1-T3） （Period Ⅰ） to the largely extensional setting as a result of the Yanshanian orogeny genetically associated with the NW-WNW-ward subduction of the paleo-Pacific oceanic lithosphere in the Late Mesozoic （J2-K2） （Period Ⅱ）. Of the Period I Indosinian granitoids, the early （T1-T2^1） ones are syn-collisional, and formed in a compressional setting; the late （T2^2-T3） ones are latecollisional, and formed in a locally extensional environment. During the Period Ⅱ Yanshanian magmatism, the Early Yanshanian （J2-J3） granitoid-volcanic rocks, which are distributed mainly in the Nanling Range and in the interior of the South China tectonic block （SCB）, are characteristic of rift-type intraplate magmatism, whereas the Late Yanshanian K1 granitoidovolcanic rocks are interpreted as genetically representing active continental margin magmatism. The K2 tholeiitic basalts interlayered with red beds are interpreted as genetically associated with the development of back-arc extensional basins in the interior of the SCB. The Yanshanian granitoid-volcanic rocks are distributed widely in South China, reflecting extensional tectonics within much of the SCB. The extension-induced deep crustal melting and underplating of mantle-derived basaltic melts are suggested as the two principal driving mechanisms for the Yanshanian granitic magmatism in South China.
基金jointly supported by National Natural Science Foundation of China(42002246,41725011 and 42002244)China Postdoctoral Scientific Foundation(Grant No.2019M660740)+2 种基金National Key R&D Plan of China(Grant No.2017YFC0601402)the Program of the Sino Probe 08-01China Geological Survey Projects(DD121201104000160916 and DD20179353)。
文摘South China as an amalgamation of the Yangtze and Cathaysia blocks is composed of Archean to Mesoproterozoic basement overlain by Neoproterozoic and younger cover.Both the constituent Yangtze and Cathaysia blocks contain well-preserved Neoproterozoic rocks that have been extensively studied in terms of the age and tectonic nature,but less is known about their earlier crustal history due to the incomplete rock record.Recent efforts in investigating the yet survived crustal nature based on isotopic and elemental signatures preserved in igneous and sedimentary rocks have steadily improved our knowledge about the pre-Neoproterozoic continental crustal evolution in South China.In this paper,we summarize the up-to-date pre-Neoproterozoic records,including petrological,geochronological,geochemical and geophysical data,across South China,and discuss its spatiotemporal patterns of the pre-Neoproterozoic crust and the relevant tectonic events.While the xenocrystic/inherited and detrital zircon records suggest widespread Archean(mainly ca.2.5 Ga)crustal components within both the Yangtze and Cathaysia blocks,exposed Archean rocks are only limited to isolated crustal provinces in the Yangtze Block.These Archean rocks are dominated by TTGs(tonalite-trondhjemitegranodiorite)with varied ages(3.3-2.5 Ga)and zircon Hf isotopes,indicating a compositionally heterogeneous nature of the Archean Yangtze Block and,by inference,the development of multiple ancient terranes.The early Paleoproterozoic(2.4-2.2 Ga)tectonomagmatic events characterize the western Yangtze Block and are supportive of an east-west subdivision of the Yangtze basement,whereas the late Paleoproterozoic(2.1-1.7 Ga)orogeneses may have affected a larger area covering both the western and eastern parts of the Yangtze Block,and also the Cathaysia Block.The eastern Yangtze Block with generally northeastward-younging late Paleoproterozoic magmatism and metamorphism likely experienced a prolonged 2.05-1.75 Ga orogenic process welding the various Archean proto-continents,consistent with the documentation of a buried late Paleoproterozoic orogenic belt imaged by deep seismic profiling from its central part and of a slightly older ophiolitic mélange in the northern part.The Cathaysia Block was probably involved in a short-lived 1.9-1.8 Ga orogenic event.The two orogeneses overlapped in time and may have contributed to the cratonization of a possible unified South China,and are referred to be linked with the assembly of the Nuna Supercontinent.The subsequent late Paleoproterozoic to early Mesoproterozoic rift successions and intrusions(1.7-1.5 Ga)in the southwestern Yangtze Block,and the ca.1.43 Ga rifting in Hainan Island of the Cathaysia Block could be responses to the Nuna break-up.Late Mesoproterozoic(1.2-1.0 Ga)magmatism of varied age and nature in different localities of the Yangtze Block is reflective of a complex tectonic process in the context of the assembly of the Rodinia Supercontinent.Similar-aged metamorphism(1.3-1.0 Ga)is recorded in Hainan Island,reflecting the Grenvillian continental collision during the Rodinia assembly,but further studies are necessar y to better constrain the late Mesoproterozoic tectonic framework of South China.
文摘The Pilbara region of Western Australia is one of only two areas on Earth–the other being the Kaapvaal Craton of southern Africa–that contain well preserved,nearcontinuous geological records of crustal evolution from the Paleoarchean into the late Paleoproterozoic.The Pilbara is famous for hosting fossil evidence of early life(stromatolites and microfossils),and for containing a record of the early Archean atmosphere.The geological record extends from granite–greenstone terranes and overlying clastic basins of the 3.53–2.83 Ga Pilbara Craton,across a major unconformity,to a series of 2.78–1.79 Ga volcanic and sedimentary successions.Between 3.53–3.23 Ga,a succession of mantle plume events formed a thick volcanic plateau on older continental crust,remnants of which include enclaves of c.3.6 Ga granitic gneiss and abundant 3.8–3.6 Ga inherited and detrital zircons.During each of the plume events,the volcanic plateau was intruded by crustally-derived granitic rocks,leading to vertical deformation by partial convective overturn.By 3.23 Ga,these processes had established thick continental crust that was then rifted into three microplates separated by c.3.2 Ga basins of oceanic crust.Subsequent plate tectonic processes to 2.90 Ga included subduction,terrane accretion,and orogeny.From 2.78–2.63 Ga the northern Pilbara Craton was affected by minor rifting,followed by deposition of thick basaltic formations separated by felsic volcanic and sedimentary rocks(Fortescue Basin).Rifting in the southern Pilbara resulted in progressively deepening marginal basin sedimentation,including thick units of banded iron formation(Hamersley Basin:2.63–2.45 Ga).
基金Fundacao Carlos Chagas de AmparoàPesquisa do Estado do Rio de Janeiro(FAPERJ),for providing him a post-doctoral fellowship(E-26/202.084/2020 and 2020.03701.1).the National Council for Scientific Development(CNPq)for financial support.CNPq for his Productivity on Research grant(#311106/2020-0)。
文摘The Archean Eon was a time of geodynamic changes.Direct evidence of these transitions come from igneous/metaigneous rocks,which dominate cratonic segments worldwide.New data for granitoids from an Archean basement inlier related to the Southern S?o Francisco Craton(SSFC),are integrated with geochronological,isotopic and geochemical data on Archean granitoids from the SSFC.The rocks are divided into three main geochemical groups with different ages:(1)TTG(3.02–2.77 Ga);(2)mediumto high-K granitoids(2.85–2.72 Ga);and(3)A-type granites(2.7–2.6 Ga).The juvenile to chondritic(Hf-Nd isotopes)TTG were divided into two sub-groups,TTG 1(low-HREE)and 2(high-HREE),derived from partial melting of metamafic rocks similar to those from adjacent greenstone belts.The compositional diversity within the TTG is attributed to different pressures during partial melting,supported by a positive correlation of Dy/Yb and Sr/Zr,and batch melting calculations.The proposed TTG sources are geochemically similar to basaltic rocks from modern island-arcs,indicating the presence of subduction processes concomitant with TTG emplacement.From~2.85 Ga to 2.70 Ga,the dominant rocks were K-rich granitoids.These are modeled as crustal melts of TTG,during regional metamorphism indicative of crustal thickening.Their compositional diversity is linked to:(i)differences in source composition;(ii)distinct melt fractions during partial melting;and(iii)different residual mineralogies reflecting varying P–T conditions.Post-collisional(~2.7–2.6 Ga)A-type granites reflect rifting in that they were closely followed by extension-related dyke swarms,and they are interpreted as differentiation or partial melting products of magmas derived from subduction-modified mantle.The sequence of granitoid emplacement indicates subduction-related magmatism was followed by crustal thickening,regional metamorphism and crustal melting,and post-collisional extension,similar to that seen in younger Wilson Cycles.It is compelling evidence that plate tectonics was active in this segment of Brazil from~3 Ga.
文摘Results of a geochemical and geochronological study of the Paleoproterozoic rock assemblage in the Haisyn block of the Ros-Tikych Domain of the Ukrainian Shield are reported.Within the block,the Haisyn Complex comprises granitoids,including pyroxene-bearing diorites,quartz diorites,granodiorites,amphibole-biotite and biotite granites,and aplite and pegmatite granites.Monazite U-Pb isotope age of charnockitic syenite belonging to the Haisyn Complex was defined at 2027±6 Ma.This age coeval with the time of granulite facies metamorphism and emplacement of numerous granitic intrusions in the area.The Sm–Nd apatite isochron yielded an age of 2100±150 Ma.TheεNd isochron value of-5 indicates a long crustal residence time of the crustal protolith.Geochemical data do not indicate any enrichment of the studied rocks in relation to the Eoarchean and Neoarchean charnockites developed in the same area.So,if the model of partial melting of the older crustal protolith is involved then the degree of melting must be quite high.However,deep negative anomalies of Sr,Eu,Zr,and Ti indicate that plagioclase,zircon,and Fe–Ti oxides probably remained unmelted in the source.The Haisyn block was buried in the lower crust at high temperature and pressure conditions in the Paleoproterozoic time.Such a situation resulted in partial melting of the existing crust and formation of melts,containing undigested zircon and bearing ancient Nd isotope signature.
文摘Having analysised the data collected by our survey ship'Ocean IV 'in the Bransfield Strait in 1991,we recognized that the geomorphology,gravity and magnetic anomalies trending NE direction along bandings. The sediments in the Bransfield Strait can be subdivided into two sequences:the first rifting equence and the second rifting sequence.The basement was faulted into a half-graben in northwestern side of the Bransfield trough. Considering the crustal structure crossing the South Shetland Islands,the Bransfield Strait and the Antarctic Peninsula, we propse a two-phase rifting tectonic evolution model and a layered-shear model for the lithospheric deformation under the effects of extensional stress field.
基金partly supported by a Grant-in-Aid for Scientific Research(B)from Japan Society for the Promotion of Science(JSPS)(No.26302009)by the NIPR General Collaboration Projects(No.26-34)to Tsunogae
文摘The Lützow-Holm Complex(LHC) of East Antarctica has been regarded as a collage of Neoarchean(ca.2.5 Ga), Paleoproterozoic(ca. 1.8 Ga), and Neoproterozoic(ca. 1.0 Ga) magmatic arcs which were amalgamated through the latest Neoproterozoic collisional events during the assembly of Gondwana supercontinent. Here, we report new geochronological data on detrital zircons in metasediments associated with the magmatic rocks from the LHC, and compare the age spectra with those in the adjacent terranes for evaluating the tectonic correlation of East Antarctica and Sri Lanka. Cores of detrital zircon grains with high Th/U ratio in eight metasediment samples can be subdivided into two dominant groups:(1) late Meso-to Neoproterozoic(1.1-0.63 Ga) zircons from the northeastern part of the LHC in Prince Olav Coast and northern Soya Coast areas, and(2) dominantly Neoarchean to Paleoproterozoic(2.8-2.4 Ga) zircons from the southwestern part of the LHC in southern Lutzow-Holm Bay area. The ca.1.0 Ga and ca. 2.5 Ga magmatic suites in the LHC could be proximal provenances of the detrital zircons in the northeastern and southwestern LHC, respectively. Subordinate middle to late Mesoproterozoic(1.3-1.2 Ga) detrital zircons obtained from Akarui Point and Langhovde could have been derived from adjacent Gondwana fragments(e.g., Rayner Complex, Eastern Ghats Belt). Meso-to Neoproterozoic domains such as Vijayan and Wanni Complexes of Sri Lanka, the southern Madurai Block of southern India, and the central-western Madagascar could be alternative distal sources of the late Meso-to Neoproterozoic zircons. Paleo-to Mesoarchean domains in India, Africa, and Antarctica might also be distal sources for the minor ~2.8 Ga detrital zircons from Skallevikshalsen. The detrital zircons from the Highland Complex of Sri Lanka show similar Neoarchean to Paleoproterozoic(ca. 2.5 Ga) and Neoproterozoic(ca. 1.0 Ga) ages, which are comparable with those of the LHC, suggesting that the two complexes might have formed under similar tectonic regimes. We consider that the Highland Complex and metasedimentary unit of the LHC formed a unified latest Neoproterozoic suture zone with a large block of northern LH-Vijayan Complex caught up as remnant of the ca. 1.0 Ga magmatic arc.
基金the Ministry of Land and Resources of the People's Republic of China(1212010711815,1212010811033)
文摘A diverse suite of Archaean gneisses at Huangbaiyu village in the North China Craton, includes rare fuchsite-bearing （Cr-muscovite） siliceous rocks - known as the Caozhuang quartzite. The Caozhuang quartzite is strongly deformed and locally mylonitic, with silica penetration and pegmatite veining common. It contains abundant 3880-3600 Ma and some Palaeoarchaean zircons. Because of its siliceous nature, the presence of fuchsite and its complex zircon age distribution, it has until now been accepted as a （mature） quartzite. However, the Caozhuang quartzite sample studied here is feldspathic. The shape and cathodoluminescence petrography of the Caozhuang quartzite zircons show they resemble those found in immature detrital sedimentary rocks of local provenance or in Eoarchaean polyphase orthog- neisses, and not those in mature quartzites. The Caozhuang quartzite intra-zircon mineral inclusions are dominated by quartz,
基金financially supported by the China Geological Survey(CGS,Grant No.DD20160183)the Major State Research Development Program of China(Grant No.2016YFC0600202)
文摘In this study, we report U–Pb and Lu–Hf isotopic data for zircons from the Mesozoic sandstones of the Upper Yangtze area, which provide critical constraints on the provenance of these sediments and further shed light on the crustal evolution of the Upper Yangtze block. The results of isotopic chronology indicate the following：（1） The provenances of the study area are very complex, and the tectonic evolution process is relatively closed.（2） The provenances are mainly Archean–Proterozoic crystalline basement or recycled material; Paleoproterozoic crustal accretion in the western margin of the Yangtze block and Neoproterozoic magmatic activities related to subduction of the western margin of the Yangtze block; early Cambrian oceanic magmatic activity, which resulted from the intraplate extension of the northern margin of the Yangtze block; late Ordovician–early Silurian magmatic activity in the northern Yangtze block and Hercynian–Indochina uplift and erosion during the Hercynian movement.（3） The Yangtze crustal growth is episodic, and an increasing amount of ancient recycled material became part of the magmatic activity, as the zircon U–Pb ages are relatively young.
