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    20 December 2004, Volume 10 Issue 4
    Article
    Post-Orogenic Granites with an Age of 1800Ma in Luliang Area, North China Craton: Constraints from Isotopic Geochronology and Geochemistry
    GENG Yuan-sheng1, YANG Chong-hui1, SONG Biao1 2, WAN Yu-sheng1 2
    2004, 10(4):  477-487. 
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    Major trace element characteristics and zircon U-Pb SHRIMP dating of the Luyashan augite-monzonites and Yunzhongshan granites in Luliang area, Shanxi Province indicate that the Luyashan augitemonzonites and Yunzhongshan granites belong to the post-orogenic granite.Zircon grains from the Luyashan augite-diorite yield a SHRIMP U-Pb age of 1 794±13 Ma and zircon grains from the Yunzhong-shan granite a SHRIMP age of 1 801±llMa. Determination of post-orogenic granites at ca.1 800 Ma provides direct evidence for constraints on the ending time of the orogeny at the end of Paleoproterozoie.
    Structure and Evolution of the Post-Collisional Fault Structures in the Three River Orogenic Belt, Exemplified by the Cenozoic Jianchuan-Lanping Basin
    LIU Jun-lai1, WANG An-jian2, CAO Dian-hua2, XIU Qun-ye2
    2004, 10(4):  488-499. 
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    The Jianchuan-Imnping Cenozoic basin is located in the Three River orogenic belt,an important tectonic belt generated during collisional or post-collisional processes due to India-Asia interaction.There are several fault zones in the basin and adjacent areas,including the Lancangjiang fault zone,the Central axis fault zone and the Qiaohou fault zone.The N-S extending Lancangjiang fault zone is characterized by occurrence of mylonites and strongly foliated granitic rocks and meta-sedimentary rocks.Foliations dip steeply either to the east or to the west with stretching lineations in the direction along their strikes.Shear sense indicators in tectonites suggest a left-lateral shear during mylonitizartion along the fault zone,The Central axis fault zone is a zone of brittle fractures in N-S direction.The fracture surfaces mainly dip to the west with dip angles varying from 0。to 90。.The shallowly dipping surfaces often cut across those with high angles form thrusts and nappe structures at different scales.Qiaohou fault zone dipping to the NNE with dip angles mainly of 60。-70。to the east is the northern extension of the Ailaoshan-Red River fault zone.Evidences for both strike-slip faulting and thrusting are obvious along the fault zone.
    Paleoproterozoic Granitic Magmatism and Metamorphism in Middle Part of Luliang Range, Shanxi Province
    YU Jin-hai, WANG De-zi, WANG Ci-yin, WANG Li-juan
    2004, 10(4):  500-513. 
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    The studies on geochronology and geochemistry of granitoid rocks in Middle Laliang Mountain,Shanxi Province indicate that there are two periods of granitic magmatism in Paleoproterozoic,occurring at ca.2 063 Ma and 1 806 Ma,respectively.The earlier adamellites are characterized by low Si02,MgO,Y and Yb concentration,high AI203,Na20,Sr,Ba concentration and high Sr/Y ratio.The later monzonitic granites are characterized by high Si02,Rb,Nb,Y and Yb concentration,low Na20,AL2O3,Sr concentration and low Sr/Y ratio.The later also exhibit lower(La/Yb)n ratio and markedly negative Eu anomalies,implying their different origins.Combined with the Sr-Nd isotopic characteristics,the Daorengou adamelites are interpreted as resulting from partial melting of Paleo-to Meso-Archean crustal materials within mantle depth,and interacting with mantle wall rocks.The Kuanping granites were produced by partial melting of the garnet granulite and decomposing of garnets in the lower crust.Geological and geochemical evidences indicate that these two periods of magmatism took place in different tectonic settings.The early adamellites were related with collision setting,and the later monzonitic granites were formed in post-orogenic setting.T-P estimates for middle-high-grade metamorphic rocks of Laliang Group indicatethat the Laliang Group experienced isothermal decompression(ITD)metamorphism with clockwise FFt paths at near same time as second granitic magmatism,indicating a rapid ascending process.The later post-orogenic granite and the metamorphism with ITD path occurred at about 1 800 Ma,when magmatism and middle-high-grade metamorphism were widespread and strong in whole North China,implying that the North China Block was in extension tectonic setting from then.
    SHRIMP Zircon U-Pb Chronology of Tonalitic Gneiss in Banqiaogou Area, Pingshan County, Hebei Province
    YANG Chong-hui1, DU Li-lin1, WAN Yu-sheng1, LIU Zeng-xiao2
    2004, 10(4):  514-522. 
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    Geochemistry of tonalitic gneisses in Banqiaogou area of Pingshan county shows high Si,A1,Na and low K.strong differentiation in its REE pattern,with higher(La/Yb)N,and distinct negative anolnalies of Nb,Ta,Ti and P,which are nearly the same as those of TTG in Archean.CL and BSE images of zircons in the tonalitic gneiss display dense regular zones and high Th/U,indicating the features of magmatic zircons,and narrow metamorphic rims with high brightness.SHRIMP dating shows that the age of the magmatic emplacement and metamorphism of these TTG gneisses are 2 536±9.8 Ma and 1 802±43Ma,respectively.The conclusion is that the West block was subducted under the East block.The subduction was responsible for the intrusion of TIG ,and finally leading to the amalgamation of Wutai block with Taihangshan block.Another independent tectonothermal event within the continent occurred at C.1.8Ga ago.
    The Effect of Differential Stress on Quartz-Coesite Transition Pressure
    ZHOU Yong-sheng, HE Chang-rong, MA Sheng-li, MA Jin
    2004, 10(4):  523-527. 
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    Coesite was produced at certain differential stress conditions below its stability field under static pressure in laboratary.which shows that differential stress has obvious effect on the quartz-coesite trailsition pressure.According to the forming conditions of coesite。there are two different physical mechanisms for shifting quartz-coesite phase transition boundary to decreased forming pressure at differential stress conditions:the phase transition in semibrittle deformation region due to local shear deformation induced mechanical instability,and the phase transition in plastic flow region due to presence of high dislocation density within highly deformed quartz induced strain instability.
    Sm-Nd, Ar Isotopic and Geochemical Characteristics of Plagioclase Amphibolites in the Bashikaogong Area, Altun Tagh Mountains
    ZHANG Zhi-cheng, GUO Zhao-jie
    2004, 10(4):  528-534. 
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    A set of schist and marble rocks with a few layers of plagioclase amphibolites are distributed to the north of Bashikaogong,Ahun Tash mountains,and experienced amphibolite facies metamorphism.These plagioclase amphibolites exhibit the features of tholeiite in their major element compositions and REE patterns,indicating their basaltic parent rocks.Four samples of these plagioclase amphibolites were analyzed for Sm-Nd isotopes.An isochron with 1 185±130 Ma was obtained whth INd=0.511 40 and ENd(t)=+5.8±0.6,suggesting that these plagioclase amphibolites were formed at the later Mesopmtemzoic and derived from the depleted mantle.Integrated with 40Ar-39Ar data of metamorphic homblendes with the greatest metamorphic age of612±5.8 Ma.it is further proved that these plagioclase amphibolites were formed during the Precambrian.These geochronological and isotopic new data give us some important information about the Late-Precambrian tectonic framework in the Ahun Tagh Mountains.
    The Representative Textures and Structures of the Seafloor Sulfide Black Smokers and Their Genetic Significance
    NIU Xiang-long, LI Jiang-hai, FENG Jun
    2004, 10(4):  535-544. 
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    Zoning,conduit,colloform ,dendritic,metasomatic,porous and infilling textures and structures are representative for the seafloor sulfide chimneys.They record the forming process and evolution history of the seafloor chimneys.The formation of different chimneys is related not only to their locations, but also to their maturities.The diffuser is another important structure in the lower sulfide mound.Diffuser is the dominant mechanism of hydrothermal advection in the mound after extinction and collapse of the black smokers.Some relicts of the sulfide black smokers have been found in the continent(i.e.in Pilbala,South Ural,Ireland,Gaobanhe etc.It is shown that the massive sulfide deposits in continent might be formed by the black smoker models as on modern seafloor.
    The Geochemical Characteristics and Tectonic Setting of the Lower Permian Basalts in Hongliuhe Area at the Border between Xinjiang and Gansu Provinces
    ZHAO Ze-hui, GUO Zhao-jie, ZHANG Zhi-cheng, SHI Hong-yu, TIAN Jie
    2004, 10(4):  545-553. 
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    The major elements geochemical characteristics of the Lower Permian tholeiitic basalts from Hongliuhe area show lower Mg,total alkali(Na2O+K2O),and higher Fe,Ti. large ion lithophile elements(LILE),such as Rb,K,Sr and Ba are enriched. The light rare earth elements(LILE)are enriched relative to heavy rare earth elements(LILE).In addition,La/Yb=10.61~16.87,,Th/Ta=1.03~1.99.Fe/Ti=5.3O~6.39,Ti/P=5.61~7.30,Ti/Zr=38.83~46.3O,Zr=(254~328)x1O-6, Zr/Y=5~10 and Y/Nb=1.52~2.45.These characteristics indicate that the magma source of the lower Permian basalts were derived from mixed components of depleted mantle(DM)and enriched mantle(EM).,The0 latter is the major end-member which reflects a low degree of partial melting of mantle source and a slight crustal contamination.
    Meozoic Tectonic Evolution of Southern Junggar Basin, Northwestern China: Constraints from Stratigraphic and Sedimentologic Evidences
    FANG Shi-hu1 2, GUO Zhao-jie1, ZHANG Zhi-cheng1, XU Huai-min3, LIU Lou-jun4
    2004, 10(4):  554-561. 
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    According to the analyses of depositional facies,seismic and geologic information,the Triassic-Jurassic depocenter was near to Urumuqi city,and the Cretaceous depocenter migrated northwards to the central part of the Junggar basin.In southern Junggar basin boundary area,the Triassic,especially the Lower Triassic,was a set of strata of braided stream to braided delta facies,suggesting the Triassic basin boundary was near to that of present day.The Lower Jurassic was alluvial-fan to fan-delta facies in Houxia area(8O km south to Urumuqi)and braided delta facies in Toutun River section.The Middle Jurassic was braided delta facies in Houxia area and meandering river to lacustrine facies in Toutun River section.The Houxia area and Tontun River sections were formed in the same sedimentary system,which suggests a southward migration of the Jurassic basin boundary toward the Houxia area.Consequently.the Junggar basin couldn't be foreland basin during the Triassic-Jurassic.The Upper Jurassic Kalazha conglomerate in southern Jungar basin and the Cretaceous basal conglomerate recorded rapid uplift and denudation during the Late Jurassic to the earliest Cretaceous.The rapid uplift and denudation might be related to the amalgamation of Lhasa block on the south margin of Eurasia plate.The basin boundary shrank obviously in Cretaceous near to southem Jungar basin boundary of present day.The Mesozoic tectonic evolution of Junggar Basin could be divided into two episodes:the extensional faulted.depression from the Triassic to Jurassic and the compressional intra-continent depression in the Cretaceous.
    The Fabric Characteristics and Origin of the Mesoproterozoic Pyritic Stromatolite from the Gaobanhe Deposits, East Hebei Province
    FENG Jun, LI Jiang-hai, NIU Xiang-long, ZHENG Jin-wu, REN Hao-jia
    2004, 10(4):  562-568. 
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    The Gaobanhe Mesoprotemzoic polymetallic sulfide deposits in East Hebei were deposited conformably on Mesoprotemzoic dolostone and black shales.Many types of pyritic stromatolites are distributed in polymetallic sulfide deposits in the form of bioherm.Pyritic stromatolites were studied by analyzing the ultrastructural morphologic characteristics and Laser Raman Specteoscopy.It is found that primary biogenic structure is preserved with pyritic stromatolites.They existed in a littoral environment.Thermophiles were flourishing in a reduced environment.which is quite close to the vents of hot water on seabed.They absorbed and enriched minerogenetic elements,reduced mineral materials from the vents, readjusted them biochemically and eventually formed pyritic stromatolites.
    Geochemical Characteristics and Tectonic Significance of the Early Cretaceous Volcanic Rocks in the Southern Margin of Jiuxi Basin
    WANG Xiao-feng, ZHANG Zhi-cheng, GUO Zhao-jie, ZHANG Chen
    2004, 10(4):  569-577. 
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    The volcanic rocks from Hanxia and Hongliuxia in Jiuxi basin are considered to be resulted from Cenozoic tectonic events.Hanxia volcanic rocks ocurr among the layers of Xiagou Formation,Xinminbao Group of the Early Cretaceous age,and have vesicular and amygdaloidal structures and distinct characteristics of underwater extrusion.These volcanic rocks ale characterized by lower SiO2 and K2O+Na2O,but relatively higher K.ΣREE in these rocks are(212~237)x 10-6.The chondrite-normalized REE patterns are smooth and right-inclined,with weak Ce anomaly and without Eu anomaly.On the primive mantle.normalized spidergrams,all the incompartible trace elements are enriched,especially LILE. There occur Nb and Ta negative anomalies,but still,compared with the primitive mantle,Nb and Ta ale not depleted. These characteristics indicate that the source of the volcanic rocks is the enriched manlte.The REE and trace elements characteristics of the Hongliuxia trachybasalts are very similar to those of Hanxia volcanics.which implies a possible common source.The tectonic setting of the volcanic rocks in Jiuxi basin is confirmed to be continental rifling by using several geochemical diagrams for basalts.This is in accordance with the structural characteristics of lower Cretaceous and the thermal history of Jiuquan basin group.Study on volcanic rocks in Jiuxi basin is significant to deepen the understanding of tectonic evolution of the basin and make clear the tectonic framework of the western China in the Mesozoic.
    Electron Microprobe Dating of Monazite and Its Application to Metamorphism in Eastern Tianshan, Xinjiang
    DANG Qing-ning, LIU Shu-wen, SHU Gui-ming, LI Qiu-gen
    2004, 10(4):  578-585. 
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    Based on chemical method of electron microprobe dating of monazite and previous improved calculating formula of ages and age uncertainties,we put forward a new formula dealing with age error on the basis of general differentiation and wrote a Visual C computer program on the Windows 2000 for calculations of age and age error.Using the new computer program,we recalculated previously published data of known ages and age errors, demonstrating the feasibility of the new formula of age error.The monazites from two metamorphic sedimentary rock samples(KM2127-5,DK2107-2)from the Eastern Tianshan were analyzed for U-Th-Pb compositions.All analyses were carried out using the JXA-8100 electron microprobe.The monazites from sample DK2107-2 record two peaks of metamorphic ages which are 341.0±3.9 Ma and 255.2±3.3 Ma.respectively.The metamorphic age of 341.0±3.9Ma is the most important period,forming an early mineral assemblage of Ky+St+Bt+Pl+Q±Or.The monazites from sample KM2127-5 display one peak of ages.262.3 4±4.4 Ma.Both the 255.2 4±3.3 Ma and 262.3 4±4.4 Ma data represent the second peak period of metamorphism,during which a mineral assemblage of Cord+Bt+P1+Or+Q were produced.The analytical results of monazite dating are well consistent with the previous 40Ar-39Ar ages, indicating that the electron microprobe dating technique for monazite and the new formula estimating age uncertainties are acceptable.
    Discovery of Mantle Xenoliths Bearing Miocene Potassium-Rich Olivine Basalt and Its Significance in Siziwangqi Area, Inner Mongolia
    CHEN Yan, WU Tai-ran, XU Xuan, ZHANG Shuang-tao
    2004, 10(4):  586-593. 
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    There is a suite of mantle xenoliths bearing olivine basalt discovered recently in the south of Siziwangqi area,Inner Mongolia.The rock is grey-black,with compact block structure and is characterized by alkaline.rich(K2O+Na20=5.91%~6.47%),high K(K2O=2.82% ~3.12%)and high Ti(Ti02=2.22% ~2.36%)compositions.The whole rock K-Ar isotopic age is 21.89 4±1.65 Ma. The rock types of xenoliths are lherzolites,spinel lherzolites and anorthositic gabbro.Geothermometer and geobarometer calculations manifest that the temperature and pressure ranges for the xenoliths are 1 100-1 250 oC and 1.2~1.7 GPa,respectively,which indicates a lithospheric mantle source.Considering that the high Ti character of the olivine basalt is similar to Hannuoba basalt,the basalt magma might come from the asthenosphere.Deep mantle plume possibly began to work since the Mesozoic under the northern margin of North China Platform,which resulted in the accumulation of vast magma remaining tinder the lithosphere,followed by underplating and ascending of some magma carrying the mantle xenoliths upwards.
    Records of Unroofing History for the Dabie UP-UHP Metamorphic Rocks in Hefei Basin
    ZHU Guang1, WANG Dao-xuan1, XU Chun-hua2, LI Xue-tian2, WANG Yong-sheng1, LIU Gou-sheng1, NIU Man-lan1
    2004, 10(4):  594-605. 
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    Sediments in the Hefei basin to the north of the Dabie orogen are important records of unroofing history for the orogen.K-Ar dating of authigenic illite proves that strata in drill-hole Ancan-1 from top to bottom are lower Cretaceous,upper-mid-lower-Jurassic.lower Permian and upper Carboniferous strata which are probably underlain by Ordovician strata.Detrital composition analysis of the Mesozoic sandstones indicates that their provenance is the Dabie orogen.Lower Permian sandstones in drill-hole Ancan-1 do not contain detrital phengite from orogen.Rich phengite(Si>3.3)detritus occurs continuously in sandstones from lower Jurassic to lower Cretaceous strata in the dril1-hole.This shows that the Dabie orogen is main provenance for the Hefei basin.and indicates that HP to UHP metamorphic rocks of the orogen were unroofed since the earliest Early Jurassic and exposed continuously since then.
    Understanding Earthquake Source Radiation
    Shengzao CHEN
    2004, 10(4):  606-614. 
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    Isolating source spectra is all important step toward for better understanding earthquake source radiation where the nucleation processes is a complex but essential area in modem seismology.To study the spectrumof ground motion radiated from the earthquake source,we must first remove the path and site effects from observed ground motions.Attenuation effects include geometric spreading,anelastic attenuation,and near-surface attenuation.There are also crustal amplification effects,which can be significant where there exists a strong velocity contrast or gradient.Comparing the earthquake source radiation from six tectonic regions: California, Mexico,Turkey,Japan,eastern North America(ENA)and British Columbia(B.C.,Canada),I found that source spectra are approximately independent of region,distance,and depth when path and site effects are properly removed.Kappa values vary regionally.The lowest kappa value corresponds to the hard rock sites in a stable intraplate environment(ENA)while generally higher kappa values correspond to the site conditions in active tectonic environments such as Japan,Mexico,B.C.,California,and Turkey.
    Cenozoic Tectonic Control on the Abiogenic CO2 Gas Deposits, Huanghua Depression
    DING Wei-wei1 2, DAI Jin-xin1 2 3, CHEN Han-lin2, YANG Chi-yin4
    2004, 10(4):  615-623. 
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    Carbon dioxide is a nonhydrocarbon gas with high economic value and bright prospects in application.In the Huanghua Depression many high-content abiogenic C02 deposits were explored since 1960's. Through analysing the distribution characteristics of abiogenic C02 deposits and their relationshipwith Cenozoic tectonic activities, it is revealed that typical abiogenic C02 is distributed along the fault belt and fault intersection zones,and most of the deposits are distributed in the middle-northern Huanghua Depression.Areas with long term faulting,strong magmatism,and high geothermal gradients favor the generation and discharge of abiogenic gas. Deep faults,as pathways for mantle magma,may provide favorable pathways for the migration of mantle gas during extension.However,these NW-NWW trending faults,such as Haihe,Xuzhuangzi and Bogezhuang,are strike-slip faults in Cenozoic and the openness condition is bad.Only in the case when deep faults are intersected by NE or NEE trending extensional faults they could become favorable sites for discharge of abiogenic gases.For example,high-content abiogenic CO2 deposits were explored in the interseetions of the Xuzhuangzi and Gan faults.Further more,the intersections are also favorable locations for the ascent of deep heat flow.The heat of fault belts stems either from deep flow or dynamic metamorphism of carbonate rocks. Cenozoic magmatic activities not only released mantle origin CO2,but also provided heat source for metamorphism of carbonate rocks.Cenozoic magmatic rocks in this area were originated from the partialmelting of uppermantle.Faulting and regional spreading promoted the generation of magma and its intrusion into the crust.These magmatic rocks are distributed along NE-NEE trending faults.Magmatism ceased in the south of Huanghua Depression following the third stage of Shahejie Period,where only weak showings of abiogenic gas in the Cenozoic formation ale known.However,in the middle-northern Huanghua Depression basalts occurred from the Shahejie Period to the Neogene and favored the discharge of abiogenic gases. The Cenozoic migration of the faulting and magmatism in Huanghua depression has close relationship with the distribution characteristics of abiogenic CO2. Most of the aboigenic CO2 is distributed in the middle-northern part.The faulting and magmatism in the middle-northern part of Huanghua Depression weremost active between Shahejie and Dongying Period.The interval between the opening and closing of the faults is short,which is good for the reservation of CO2.
    Turbidite Characteristics of Delta Front for the 3rd Member of Shahejie Formation in Niuzhuang Sag, Jiyang Depression
    RAO Meng-yu1, ZHONG Jian-hua1, GUO Ze-qing1, YANG He-shan1, LIU Jin-you2
    2004, 10(4):  624-633. 
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    Based on the comprehensive analysis of geological,well logging and seismic data,the turbidite characteristics of delta front in the 3rd Member of Shahejie Formation in Niuzhuang sag are studied.The results show that there are two turbidity sedimentary types in this area,namely the sandy turbidite andmuddy turbidite.The former has finer granularity and lower maturity of composition and texture,with characteristics of slumping redeposit and can be described by Bouma sequence,such as CDE,BCD and ABCD.Furthermore.the sandy turbidite can be classified into two subtypes:the turbidite sandbody with supplying channel and the turbidite sandbody without supplying channel. The former subtype has fan shaped distribution that can be further subdivided into five microfacies:inner-fan channel,middle-fan braided channel,space between middle-fan braided channel,middle-fan braided channel front and outer fan.The latter has slice and tongue shaped distribution and can be further subdivided into two microfacies: central section and marginal section.There are two subtypes of muddy turbidites developed in this area:graded straticule mudstone and inhomogeneous massive mudstone.The muddy turbidites can not be described in Bouma sequences,and their origins are of low-density turbidity currents. According to sedimentary characteristics of turbidity sediments,a integrated depositional mode of the delta and turbidites in this area are established .Meanwhile,the genesis of delta front turbidites and their significance in petroleum geology are discussed.
    Migration of Elements between Granulites and Their Retrograded Metamorphic Rocks in Tongde and Shaba Area, Western Sichuan Province
    YU Hang-bo, XU Shi-jin, WANG Ru-cheng, SUN Hai-ting, LIU Wen-zhong and FANG Zhong
    2004, 10(4):  634-648. 
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    A geochemical study of elemental migration from granulite-facies rocks to amphibolite-facies rocks during retrograde metamorphism has been carried out through the analyses both of petrochemical data for whole rocks and electronic microprobe data for essential minerals(e.g.hypersthene,augite andhornblende)in the rocks.The removal variations of compositions for major elements in the whole rocks and their essential minerals are similar,which suggests that such changes were most likely controlled by the transformation of main mineralogical phases and the fluid/rock interaction during the retrograde metamorphism.Abundances of K,Rb,Cs,Fe3+ ,Ti,LREE of whole rocks are gradualy increased from Tongde granulites to biotite-hornblende plagiogneisses,while abundances of Li,Ca,Mg,Fe2+,V,Co,Pb,P and HREE decreased In addition,the elements such as Na, Be, Rb, Y, Nb, Ta, Th, U, Cr, Ni,REE are increased from Shaba granulites to epidote-hornblende plagiogneisses,while Li,K,Ti,Fe,Mn,Mg,V,Co,Zn,Pb decreased . Many lithophile elements and LREE are enriched and some transitional elements are depleted in the highly retrograded rocks from granulites,therefore the authors suppose that the metamorphic fluids in the retrograde metamorphic process could be derived from upper-crust reservoirs.Due to the fluid/rock interaction many chemical elements in granulites including REE were activated and migrated in the prolonged duration of retrograde metamorphism.