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2003 Vol. 14, No. 2

Display Method:
Kanfenggou UHP Metamorphic Fragment in Eastern Qinling Orogen and Its Relationship to Dabie~Sulu UHP and HP Metamorphic Belts, Central China
Suo Shutian, Zhong Zengqiu, Zhou Hanwen, You Zhendong
2003, 5(2)
Abstract:
IntheCentralOrogenicBelt,China,twoUHPmetamorphicbeltsarediscriminatedmainlybasedonadetailedstructuralanalysisoftheKanfenggouUHPmetamorphicfragmentexposedintheeasternQinlingorogen,andtogetherwithpreviousregionalstructural,petrologicalandgeochronologicaldataatthescaleoftheorogenicdomain.ThefirstonecorrespondstotheSouthAltunNorthQaidamNorthQinlingUHPmetamorphicbelt.TheotheristheDabieSuluUHPandHPmetamorphicbelts.ThetwoUHPmetamorphicbeltsareseparatedbyaseriesoftectonicslicescomposedbytheQinlingrockgroup,DanfengrockgroupandLiulingorFozilingrockgroupetc.respectively,andaredifferentinageofthepeakUHPmetamorphismandgeodynamicimplicationsforcontinentaldeepsubductionandcollision.RegionalfieldandpetrologicalrelationshipssuggestthattheKanfenggouUHPmetamorphicfragmentthatcontainsalargevolumeofthecoesite~andmicrodiamond~bearingeclogitelensesiscompatiblewiththestructuresrecognizedintheSouthAltunandNorthQaidamUHPmetamorphicfragmentsexposedinthewesternpartofChina,therebyformingalargeUHPmetamorphicbeltupto1000kmlongalongtheorogenstrike.ThisUHPmetamorphicbeltrepresentsanintercontinentaldeepsubductionandcollisionbeltbetweentheYangtzeandSino~Koreancratons,occurredduringthePaleozoic.Ontheotherhand,thewell~constrainedDabie~SuluUHPandHPmetamorphicbeltsoccurredmainlyduringTriassictime(250~220Ma),andwereproducedbytheintracontinentaldeepsubductionandcollisionwithintheYangtzecraton.TheKanfenggouUHPmetamorphicfragmentdoesnotappeartolinkwiththeDabie~SuluUHPandHPmetamorphicbeltsalongtheorogen.ThereisnoreasontoassumethetwoUHPmetamorphicbeltsasasinglegiantdeepsubductionandcollisionzoneintheCentralOrogenicBeltsituatedbetweentheYangtzeandSino~Koreancratons.Therefore,anydynamicmodelfortheorogenmustaccountforthedevelopmentofUHPmetamorphicrocksbelongingtotheseparatetwotectonicbeltsofdifferentageandtectono~metamorphichistory.
Sedimentary Facies Architectures of Third~Order Sequences from Early to Middle Triassic in Nanpanjiang Basin
Mei Mingxiang, Ma Yongsheng, Deng Jun, Gao Jinhan, Chen Huijun, Meng Qingfen, Li Donghai
2003, 5(2)
Abstract:
TherearecomplexandregularchangesonsedimentaryfaciesfromtheEarlytotheMiddleTriassicintheNanpanjiangbasin.AftertheobviousdrownedeventofcarbonateplatformsinthetransitionalperiodbetweenPermianandTriassic,carbonateplatformshaveevolvedintotheramptypefromtherimmed~shelftype.Thedifferentiationofsedimentaryfaciesbecomesclearerinspace,whicharemarkedbythechangesfromanattachedplatformtoaturbiditybasinandseveralisolatedplatformsinthebasin.ThestrikingcharacteristicsarethedevelopmentofooliticbanksonisolatedplatformsinNanningandJingxiandthereef~andbank~limestonesinthemarginoftheattachedplatformintheEarlyTriassic.Despitethedifferenceofthetime~spanandthearchitectureoffaciessuccessionofthirdordersedimentarysequences,theprocessofthethird~orderrelativesea~levelchangesreflectedbythesedimentaryfaciessuccessionofthethird~ordersequencesisgenerallysynchronous.Therefore,sixthird~ordersequencescouldbediscernedinthestratafromtheEarlytotheMiddleTriassicintheNanpanjiangbasin.Usingtwotypesoffacieschangingsurfacesandtwotypesofdiachronismsinstratigraphicrecordsasthekeyelements,thesedimentaryfaciesarchitecturesofthethird~ordersequencesthatrepresentsequencestratigraphicframeworksfromtheEarlytotheMiddleTriassicintheNanpanjiangbasincouldbeconstructed.
Raman Spectrum Study on Quartz Exsolution in Omphacite of Eclogite and Its Tectonic Significances
Wang Lu, Jin Zhenmin, He Mouchun
2003, 5(2)
Abstract:
ThestudiesonultramicrostructurecharacteristicsofquartzexsolutionineclogiteandcoesiteinUHPeclogiteofseverallocalitiesaredonewiththeapplianceoflaserRamanspectroscopyandU~stage.Researchresultsshowthatthephasetransformationofcoesite~quartzingarnetand/oromphaciteisacontinuousprocess.Topologicalrelationshipispresentbetweenquartzexsolutioninomphaciteanditshostmineralwhichshowsorientationsoftwolongaxesofquartzexsolutionparallelto(100)and(-101)ofomphacite.Atpresent,somescholarssuggestthatthequartzexsolutioninomphaciteofeclogiteistheevidenceofUHPmetamorphism.However,temperatureandpressureconditionandtheexsolutionmechanismoforientedneedlelikequartzinomphacitestillremainunclear.Therefore,furtherstudyshouldbeenhancedonexperimentalresearchonexsolutionmechanismofsuper~silicateclinopyroxene,whichcouldprovideexperimentalquantitativeconstraintonquartzexsolutionasUHPindicator.
Organic Geochemistry Characteristics in Ores and Host Rocks from Qixiashan Lead Zinc Deposit, Nanjing, China
Xie Shucheng, Wang Hongmei, Guo Jianqiu, Liang Bin, Zhou Xiugao
2003, 5(2)
Abstract:
Organicmatter,associatedwithores,hostrocks,oresourcerocksandpresentinfluidinclusionsintheQixiashanlead~zincpolymetallicdeposithostedinUpperCarboniferousdolomitesandlimestonesinEastChina,wassystematicallyanalyzedusingFouriertransforminfraredspectroscopy,gaschromatography(GC),GC/massspectrometryandproton~inducedX~rayemission.ThebiomarkerratiosofnC-21/nC+22~alkanes,C23tricyclic/C30~hopaneandthetricyclicterpaneparametersincludingC21/C23,C19-20/C21-29andC19-25/C26-29caneffectivelydiscriminateoresfromhostrocks.Extractableorganicmatterpresentinfluidinclusionsdisplayssimilaritiestothoseenclosedintheoresourcerocksinthebiomarkerratios,suggestingthataproportionoforganicmatterwasintroducedintothedepositfromtheoresourcestrata.ThepresenceofcopperandzincinstageⅡpyrobitumenindicatesthatsomemetalsmayhavebeentransportedbyanorganicfluidorremovedfromanaqueousfluidbyorganicmatter.
Petrographic of Northwestern Sudan
Nafi M, Abdullatif O M
2003, 5(2)
Abstract:
The sedimentology of the Northwestern Sudan consists of lower, middle and upper cycles. The lower and upper cycles are composed of intercalated fluvial and shallow marine facies, whereas the middle cycle consists entirely of fluvial and glaciofluvial facies. The petrographic analysis shows that the lower and upper cycles consist of quartz and lithic arenite sandstones, whereas the middle cycle consists of arkosic and lithic arenite sandstones. The lower and upper cycle sandstones reflect derivation mainly from recycled orogens with minor contribution from craton interior provenances. However, the middle cycle sandstones indicate derivation from basement uplift, transitional and mainly recycled orogens provenances.
Assessment of Rock~Eval Tmax Data in Bambra 2 Well of Barrow Sub~basin, North West Shelf of Australia: A Case Study of Contaminated Rock~Eval Data
He Sheng, Alex Kaiko, Mike Middleton, Jiang Chunqing
2003, 5(2)
Abstract:
Thecontaminationofcuttingsandside~wallcore(SWC)samplesintheBambra~2wellbydrilling~mudadditivesandnaturalhydrocarbonsmaycauseRock~EvalTmax(℃)datatobesuspect,andaffectitsutilityintheassessmentofthermalmaturity.TheRock~Evalresultsof284cuttingssamples,31side~wallcoresamplesandconventionalcoresamplesfromtheJurassic~CretaceoussedimentarysequencesintheBambra~2wellarepresentedinthispaper.SignificantlylowerTmaxvaluesfromcuttingssamplescomparedwithTmaxvaluesfromconventionalcoresamplesandsolventextractedSWCsamples,fromthedeeperandhighermaturityinterval,arethoughttohavebeencausedbycontaminationbydieselandotherdrilling~mudadditives.ThecuttingssamplesintheBarrowGroupofCretaceousmaybecontaminatedbynaturalhydrocarbons,resultingtheirTmaxvaluestobe2~10℃lowerthanaregularlyincreasedTmaxtrendfromcoresamples.ThisstudyindicatesthatmorereliableRock~EvalTmaxdataareobtainedfromtheconventionalcoresamplesandsolventextractedSWCsamples.ThisstudyalsoindicatesthattheTmaxvaluesfromsomeSWCsampleswerealsoaffectedbyfreehydrocarbons,duetotheuseofdieselasamudadditiveaswell