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2008 Vol. 19, No. 2

Display Method:
Geochronology Constraints on Transformation Age from Ductile to Brittle Deformation of the Shangma Fault and Its Tectonic Significance, Dabieshan, Central China
王国灿, 王朴, 刘超, 王岸, 叶润清
2008, 10(2)
Abstract:
ByadetailedinvestigationofgeometryandkinematicsoftheShangma(商麻)faultinDabieshan(大别山),threedifferentcrustlevelsofextensionmovementhavebeenrecognizedinsequencefromthedeeptotheshallow:①low-angleductiledetachmentshearingwithtoptotheNW;②low-anglenormalfaultwithtoptotheNWorNWWinbrittleorbrittle-ductiletransitiondomain;③high-anglebrittlenormalfaultwithtoptotheWorNWW.TwosampleswerechosenforzirconU-PbagedatingtoconstraintheactivityageoftheShangmafault.Abeddingintrusivegranitoidpegmatiteveinthatisparalleltothefoliationofthelow-angleductiledetachmentshearzoneofthecountryrockexhibitsalotus-jointtypeofboudinagedeformation,showingsyn-tectonicemplacingattheendoftheductiledeformationperiodanddeformationinthebrittle-ductiletransitiondomain.ThezirconU-Pbdatingofthisgranitoidpegmatiteveingivesanageof(125.9±4.2)Ma,whichexpressestheextensioninthebrittle-ductiletransitiondomainoftheShangmafault.Theothersample,whichiscollectedfromagraniteplutoncuttingthefoliationofthelow-angleductiledetachmentshearzone,givesazirconU-Pbageof(118.8±4.1)Ma,constrainingtheendoftheductiledetachmentshearing.Thenthetransformationagefromductiletobrittledeformationcanbeconstrainedbetween126–119Ma.Combinedwiththepreviousresearches,theformationoftheLuotian(罗田)dome,whichislocatedtotheeastoftheShangmafault,canbeconstrainedduring150–126Ma.ThisstudygivesanewtimeconstrainttotheevolutionoftheDabieorogenicbelt.
Zircon U-Pb Age, Trace Element, and Hf Isotope Evidence for Paleoproterozoic Granulite-Facies Metamorphism and Archean Crustal Remnant in the Dabie Orogen
雷能忠, 吴元保
2008, 10(2)
Abstract:
ZirconU-Pbage,traceelements,andHfisotopesweredeterminedforgranuliteandgneissatHuangtuling(黄土岭),whichishostedbyultrahigh-pressuremetamorphicrocksintheDabie(大别)orogen,east-centralChina.Cathodoluminescence(CL)imagesrevealcore-rimstructureformostzirconsinthegranulite.Thecoresshowoscillatoryzoning,relativelyhighTh/Uand176Lu/177Hfratios,andhighrareearthelement(HREE)-enrichedpattern,consistentwithmagmaticorigin.Theygaveaweightedmean207Pb/206Pbageof(2766±9)Ma,datingmagmaemplacementofprotolith.Therimsarecharacterizedbysectororplanarzoning,lowTh/Uand176Lu/177Hfratios,negativeEuanomaliesandflatHREEpatterns,consistentwiththeirformationundergranulite-faciesmetamorphicconditions.ZirconU-Pbdatingyieldsanageof(2029±13)Ma,whichisinterpretedasarecordofmetamorphiceventduringtheassemblyofthesupercontinentColumbia.Thegneisshasaprotolithageof(1982±14)Ma,whichissimilartothezirconU-Pbageforthegranulite-faciesmetamorphism,suggestingcomplementaryprocessestogranulite-faciesmetamorphismandpartialmelting.Afewinheritedcoreswithigneouscharacteristicshave207Pb/206Pbagesofapproximately3.53,3.24,and2.90Ga,respectively,suggestingthepresenceofMesoarcheantoPaleoarcheancrustalremnants.AfewTriassicandCretaceousmetamorphicageswereobtained,suggestingtheinfluencesbytheTriassiccontinentalcollisionandpostcollisionalcollapseinresponsetotheCretaceousextension.ComparingwithabundantoccurrenceofTriassicmetamorphiczirconsinultrahigh-pressureeclogiteandgranitcgneissfromtheDabie-Sulu(苏鲁)orogenicbelt,however,verylimitedavailabilityofaqueousfluidorhydrousmeltisevidentforzircongrowthintheHuangtulinggranuliteandgneissduringthecontinentalcollision.Themagmaticprotolithzirconsfromthegranuliteshowalargevariationin176Hf/177Hfratiosfrom0.280809to0.281289,correspondingtoeHf(t)valuesof-7.3to6.3andHfmodelagesof2.74to3.34Ga.The2.90GainheritedzirconsshowthesimilarHfisotopefeatures.Theseindicatethatbothgrowthofjuvenilecrustandreworkingofancientcrusttookplaceatthetimeofzirconformation.Itisinferredthat&
Response of Glacier and Lake Covariations to Climate Change in Mapam Yumco Basin on Tibetan Plateau during 1974-2003
叶庆华, 姚檀栋, 陈锋, 康世昌, 张雪芹, 王毅
2008, 10(2)
Abstract:
ThestudyofspatialandtemporalcovariancesofglaciersandlakeswouldhelpustounderstandtheimpactofclimatechangewithinabasininTibet.ThisstudyfocusesonglacierandlakevariationsintheMapamYumco(玛旁雍错)basin(covering7786.44km2)byintegratingseriesofspatialdatafromtopographicmapsanddigitalsatelliteimagesatfourdifferenttimes:1974,1990,1999,and2003.Theresultsindicatethat:(1)decreasedlakes,retreatedglaciers,enlargedlakesandadvancedglaciersco-existinthebasinduringthelast30years;(2)glacierrecessionwasacceleratedinrecentyearsduetothewarmerclimate;(3)lakeareasinthebasinarebothreducedandenlargedbyanacceleratedspeedwithmorewatersuppliesfromspeedingmeltglaciersorfrozengroundinthelastthreedecades.
In Situ Resonance Raman Spectra of Organic Pigments in Momo Coral
Fan Luwei* (范陆薇), Yang Mingxing (杨明星)
2008, 10(2)
Abstract:
Inthisstudy,Ramanscatteringmeasurementswereobtainedformomocoralscoveringtheirtypicalrangeofcolors.Threedifferentexcitationwavelengths(785,633,514nm)areusedforthesamesamplesatthesamepoints.AllthesamplesshowthetwomajorRamanfeaturesofpolyeniccompoundsassignedtodoublecarbon-carbon(C=C)stretchingvibrationatapproximately1500cm-1andsinglecarbon-carbon(C—C)stretchingvibrationatapproximately1130cm-1bondstretchingmode.Thesepeaksarenotdetectedinthecorrespondingwhitepartsofmomocorals.However,somechangesinintensities,shape,andpositionofC=Cstretchingvibrationsofthesamepointareobservedbyusingdifferentexcitationwavelengths.TheexactpositionofC—Cstretchingvibrationofpolyenicmoleculesdependsstronglyonthenumberofdoublebondscontainedintheirpolyenicchain.Inaddition,thenumberofdoublebondscontainedinthepolyenicchainsshowsthatdifferentcolorsoftheredmomocoralarecausedbydifferentmixturesofpolyeniccompounds.
Bottom Simulating Reflector and Gas Seepage in Okinawa Trough: Evidence of Gas Hydrate in an Active Back-Arc Basin
栾锡武
2008, 10(2)
Abstract:
Tolookforgashydrate,22multi-channeland3single-channelseismiclinesontheEastChinaSea(ECS)shelfslopeandatthebottomoftheOkinawaTroughwereexamined.Itwasfoundthattherewasindeedbottomsimulatingreflector(BSR)occurrence,butitisveryrare.BesidesseveralBSRs,agasseepagewasalsofound.Asshownbythedata,boththeBSRandgasseepageareallrelatedwithlocalgeologicalstructures,suchasmuddiapir,anticline,andfault-controlledgraben-likestructure.However,similarstructural“anomalies”arequitecommoninthetectonicallyveryactiveOkinawaTroughregion,butveryfewofthemhavedevelopedBSRorgasseepage.Thearticlepointsoutthatthemainreasonisprobablythelowconcentrationoforganiccarbonofthesedimentinthisarea.Itwasspeculatedthattherareoccurrenceofgashydratesinthisregionisgovernedbystructure-controlledfluidflow.Numerousfaultsandfracturesformanetworkofhigh-permeabilitychannelsinthesedimentandhighlyfracturedigneousbasementtoallowfluidcirculationandventilation.Fluidflowinthistectonicenvironmentisdrivenprimarilybythermalbuoyancyandtakesplaceonawiderangeofspatialscales.Thefluidflowmayplaytworolestofacilitatehydrateformation:tohelpgatherenoughmethaneintoasmallareaandtomodulatethethermalregime.
Influence of Salt Beds on the Segmentation of Structure and Hydrocarbon Accumulation in Qiulitag Structural Belt, Tarim Basin, China
范秋海, 吕修祥, 杨明慧, 谢会文
2008, 10(2)
Abstract:
SeismicinformationandbalancedprofiletechnologywereusedtorevealtheinfluenceofthesaltbedinsegmentationofstructureandhydrocarbonaccumulationinQiulitagstructuralbeltinTarimbasin.Fromwesttoeast,theshorteningofstrataabovethesaltbedsgraduallydecreases,while,theshorteningbelowthesaltbedsgraduallyincreases,whichshowsthatthesegmentationofstructureintegratedtheseismicprofile.Thereisgreatdifferenceofthedeformationofstratabelowandabovethesaltbedsbetweenthewestsegmentandtheeastsegment.Theanalysisofthedistributionofoil/gasfieldsandthehydrocarbonpropertiesindicatesthesimilarsegmentationtothestructuresegmentation.ThesaltbedsinrelativelyshallowlayerschangethestressconditionfrombasementofKuqaforelandbasin,whichleadstothesegmentationofQiulitagstructuralbelt.Becausethesaltbedsinthewestsegmentcameintobeingearlierthanthoseintheeastsegment,thewestsegmentcaptureshydrocarbonfromtwosetsofsourcerock,whiletheeastsegmentcanonlycapturehydrocarbonsfromonesetofsourcerock.So,thesaltbedsplayanimportantroleinthesegmentationofstructureandhydrocarbonaccumulation.
Tephra Discovered in High Resolution Peat Sediment and Its Indication to Climatic Event
程胜高, 毛绪美, 王凤林, 洪业汤, 朱咏煊, 安琪
2008, 10(2)
Abstract:
Floatingtephrawasdepositedtogetherwithicecore,snowlayer,abyssalsediment,lakesediments,andothergeologicalrecords.Itisofgreatsignificancetointerprettheimpactontheclimatechangeofvolcaniceruptionsfromthesegeologicalrecords.ItisthefirsttimethatvolcanicglasswasdiscoveredfromthepeatofJinchuan(金川)Maar,Jilin(吉林)Province,China.Anditisinsitusedimentsfromanear-sourceexplosiveeruptionaccordingtoparticlesizeanalysisandidentificationresults.ThetephrawereneitherfromTianchi(天池)volcanoeruptions,Changbai(长白)Mountain,norfromJinlongdingzi(金龙顶子)volcanoabout1600aBPeruption,butmaybefromanunknowneruptionofLonggang(龙岗)volcanogroupaccordingtotheirgeochemistryanddistribution.GeochemicalcharactersofthetephraaresimilartothoseofJinglongdingzi,whicharepoorinsilica,deficientinalkali,Na2OcontentismorethanK2Ocontent,andaresimilartodistributionpatternsofREEandincompatibleelements,whichhelpstospeculatethattheyoriginatedfromthesamemantlemagmawithrarecondemnation,andfrombasalticexplosiveeruptionofLonggangvolcanogroup.Thetephra,frompeatwithageprovedthattheeruptionpossiblyhappenedin15BC–26AD,isoneofLonggangvolcanogrouperuptionthatwasnotrecordedandisearlierthanthatofJinglongdingziabout1600aBPeruption.Andthesedimentarytimeoftephraisduringtheperiodoflowtemperaturealteration,whichmaybetheinfluenceoferuptiontowardthelocalclimateaccordingtothecorrelativityoferuptiontolocaltemperaturecurveofpeatcelluloseoxygenisotope.
Application of Three-Dimensional Laser Scanning and Surveying in Geological Investigation of High Rock Slope
Huang Runqiu* (黄润秋), Dong Xiujun (董秀军)
2008, 10(2)
Abstract:
Theappearanceof3Dlaserscanningtechnologyisoneofthemostimportanttechnologyrevolutionsinsurveyingandmappingfield.Itcanbewidelyusedinmanyinterrelatedfields,suchasengineeringconstructionsand3Dmeasurements,owingtoitsprominentcharacteristicsofthehighefficiencyandhighprecision.Atpresentitsapplicationisstillintheinitialstate,anditisquiterarelyusedinChina,especiallyingeotechnicalengineeringandgeologicalengineeringfields.Startingwithageneralintroductionof3Dlaserscanningtechnology,thisarticlestudieshowtoapplythetechnologytohighrockslopeinvestigations.Bywayofacasestudy,principlesandmethodsofquickslopedocumentationandoccurrencemeasurementofdiscontinuitiesarediscussedandanalyzed.Analysisresultsshowthattheapplicationof3Dlaserscanningtechnologytogeotechnicalandgeologicalengineeringhasagreatprospectandvalue.