简介:Thebookfollowsthehistoricalcourseofthedevelopmentofgeologicalscience,fromthetimeofancientcivilisationsintheMediterraneanregion,uptothepresentday.However,thebeginningofgeologyasamodernscienceisgenerallyconsideredtodatefromtheobservationoftheDevonianunconformityatSiccarPointnearEdinburghbyHuttonaround1788.ThisfollowedobservationshemadeatGlentiltofgranitecuttingtheschistositvplanesoftheschists,
简介:Forskarntypedeposits,therearetwokindsofskarns,skarnformedbyfiltrating-diffusingmetasomatismandveinskarnformedbyfilling.Theveinskarn,discussedthispaperandconsideredtobemagmaticgenesis,ischaracterizedby:(1)occurringasveinwithdistinctboundarieswithcountryrocks,yetjustthesameeveninmarbleeasytobereplaced;(2)composedofamineralassemblagesimi-lartothatofgranite,containingpegmatiteaswellascoarseskarnmineralpockets,andsometimestran-sitedwithdikerocks;(3)clearcrystallinefeatureofdeposition;(4)sideronintietexture;(5)showingvesicular,bean-likeandflowstructures;(6)verycommonliquidimmiscibility;(7)verticalzoningofgravitationaldifferentiationcausedbyvolatileconcentrationupwards;(8)associatedandtransitedwithiron-copperorebodiesofmagmaticgenesisandtungsten-bearingquartzveinsofsilicatemagmaticgene-sisrichinvolatile;(9)meltinclusions.Twooriginsofskammagma,originatedbyassimilationofsilicatemagmaatitsemplacem
简介:By"concealedexplosionofmagma",wemeantheexplosiveproessofmagmaundersubterraneanconcealedconditionswhichisessen-tiallysimilartovolcaniceruptionseenatthesurface;theonlydiffer-"nceisthatthelattertakesplaceinanopenenvironmentatthesurface’`vhiletheformertinasemi-openenvironmentbelowathincovernearlhesurfac
简介:TheultramaficdikesintheTarimlargeigneousprovince(TarimLIP),exposedintheXiaohaiziareainthenorthwesternTarimBasinofnorthwesternChina,haveporphyritictextures,andtheolivineandclinopyroxeneareasthemajorphenocrystphases.Thegroundmassthereinconsistsofclinopyroxene,plagioclaseandFe-Tioxides,withthecryptocrystallinetexture.TheolivinephenocrystsinonetypicalultramaficdikehaveFo(Mg/(Mg+Fe))numbersrangingfrom73to85,whicharenotinequilibriumwiththeolivine(Mg#of89)fromthehostrockcrystalized.Combinedwithmicroscopeobservation,boththeolivineandclinopyroxenephenocrystsaswellassomeFe-Tioxidesintheultramaficrockareaccountedascumulates.Theliquid(parentalmagma)compositionofSiO2of45.00wt.%–48.82wt.%,MgOof9.93wt.%–18.56wt.%,FeOof5.85wt.%–14.17wt.%,CaOof7.54wt.%–11.52wt.%,Al2O3of8.70wt.%–11.62wt.%andTiO2of0.00wt.%–3.43wt.%intheXiaohaiziultramaficrockwasestimatedbymassbalance,andtheresultsshowareasonableliquidproportioninthecumulate-bearingultramaficdike(ca.45%–60%inthewholerock).Theestimatedparentalmagmacompositioncorrespondstoameltingtemperatureof1300–1550oC,whichisequalorhigherthanthoseofanormalasthenospheremantle,supportingtheinvolvementofamantleplume.Combinedwithotherpreviousstudies,anevolutionmodelfortheformationprocessesoftheXiaohaiziultramaficdikeoftheTarimLIPisproposed.
简介:TheZhoukoudianstockinBeijingisaconcentriczonedcomplexintrusivebodyformedbytwosuccessiveintrusions.Quartz-dioriteformedbythefirstintrusionisscatteredsparselyonthemarginsofthebody,whilegranodioriteresultingfromthesecondintrusionconstitutesthemainpartoftheintrusion.Itexhibitsthreedistinctpetrographiczonesmacroscopically,andischemicallycharacterizedbyenrichmentofhigh-temperaturecomponents,suchasMg,Ca,Sc,Ti,Cr,Mn.FeandCo,onitsborderandmerelyslightenrichmentofsomelow-temperaturecomponents,suchasNaandSi,initscentralpart.Aseriesofstructuralfeaturesindicatethatthedeformationoftheintrusionandthermo-metamorphicrocksbecomesweakerwithanincreaseofdistancefromthecontact,andthattheintrusivebodyisaproductofballooningorinflatingdiapiricemplacement.Basedoncalculationsofthedensity,viscosityandyieldstrengthofmagmaandthereasonablediffusionconstantsandoxygenisotopicdata,themechanismofthecompositionalzonationofthemajorpartofthestockisdiscussed.ItisconsideredthattheSoreteffect,combinedwithdouble-diffusiveconvection,canexplainthecompositionalzonationoftheintrusion.Calculationoftheascentratesofmagmashowsthatsuccessiveupwellingofmagmagotfasterandfasterwiththeprogressoftime.
简介:WudalianchivolcanicrocksarethemosttypicalCenozoicpotassicvolcanicrocksineastenChina.Compositionalcomparisonsbetweenwholerocksandglassesofvariousoccurrencesindicatethatthemagmatendstobecomerichinsilicaandalkalisasaresultofcrystaldifferentiationinthecourseofevolu-tion.TheyareuniqueinisotopiccompositionwithmoreradiogenicSrbutlessradiogenicPb.^87Sr/^86Srishigherand^143Nd/^144Ndislowerthantheundifferentiatedglobalvalues.Incomparisontocontinentalpot-ashvolcanicrocks,Pbisotopesareapparentlylower.Thesevariousthreadsofevidenceindicatethattherockswerederivedfromaprimaryenrichedmantlewhichhadnotbeensubjectedtoreworkingandshowsnosignofincorporationofcrustalmaterial.ThecorrelationbetweenPbandSrsuggeststheregionalheterogeneityintheuppermantleintermsofchemicalcomposition.
简介:Liquidseparationofmagmaisreferredtoakindofdiffcrentiationofmagmawhichtakesplaceinthecaseofthatmeltsareimmiscibleorlimitedlymiscibleeacliother.Itplaysanimportantroleintheform-ingofbasic,ultrabasicrocksandoredepositsrclatedtotho8ekindsofrocks.Butitisnotsurewhethcritmayoccurintheprocessoftheformingofin
简介:NumerousdarkenclaveswithdifferentshapesarefoundinJiulingNeoproterozoicgranitoids.PreciseLAICP-MSU-Pbdatingwasconductedonzirconsextractedfromtwomicrocrystallineenclavesamples,yieldingcrystallizationagesof822.6±5.8Maand822.2±6.2Ma,respectively.Theconsistentageswithinanalyticalerrorswiththehostgranitoidssuggestedthattheyweretheproductsofthesamemagmatism.Themicrocrystalline-dioriticenclavescommonlyshowplasticformsandcontainsimilarplagioclasemegacryststothehostrocks,andbothoftheenclavesandhostgranitoidsshowedacomplexcompositionandstructuralimbalanceinplagioclases.Furthermore,theapatiteswithaeuhedralacicularshapeoccurredwidelyinthemicrocrystalline-dioriticenclaves.Allofthesepetrographicfeaturesaboveimplymagmamixingisinvolvedintheirdiagenesis.TheenclavesandhostgranitoidsshowamarkedzircontraceelementdifferenceandHfisotopicsignatureswithoutcorrelationinzircontraceelementpairsbutformtheirownsystembetweenenclavesandhostgranitoids.Additionally,mostofthezirconsshowextremelyhighεHf(t)withεHf(t)=3.54?11.94fromthesouthernsamples,andεHf(t)=1.0?9.09fromthecentralregion.SomezirconswiththehigherεHf(t)aresimilartothezirconsfromthejuvenileislandarcintheeasternsegmentofJiangnanOrogen.IntegratedgeologicalandHfisotopiccharacteristicssuggestmicrocrystalline-dioriticenclaveswerederivedfromthepartialmeltingprocessoftheMesoproterozoiccrustwhichenrichedjuvenileislandarcmaterialsandmixedwiththegraniticmagmathatremeltedfromtheMesoproterozoiccontinentalcrustwhichrelativelyenrichedancientsedimentsandmixedwiththehostgranitoidindiagenesis.
简介:Ti-richgarnetisfoundwithincalciticijolitefromtheOkacarbonatitecomplexinCanada,whichischaracterizedby58%–73%andraditecomponent(2.12wt.%–4.18wt.%TiO2)andclassifiedasmelanite.Thegarnetdisplayscomplexzoningandcontainsabundanthighfieldstrengthelements(HFSEs)andrareearthelements(REEs).Threegroups(Ⅰ,Ⅱ,Ⅲ)havebeenidentifiedbasedontheirpetrographicnature.ComparedtogroupsⅡandⅢ,GroupⅠgarnetcorescontainhigherTiO2,MgO,HFSE,andREEandlowerSiO2abundances.Thedistinctchemicalandpetrographicsignaturesoftheinvestigatedgarnetscannotbeattributedtosimpleclosedsystemcrystallization,buttheyareconsistentwiththemulti-pulsemagmamixing.CombinedwithpreviouslyreportedU-Pbagesforapatitefromthecalciticijolite,atleastthreestagesofmagmaevolutionandsubsequentmixinghavebeeninvolvedinthegenerationofcalciticijoliteatOka.Theearly-formedmeltthatgeneratedGroupIgarnetcorewaslatermixedwithatleasttwosmall-volume,moreevolvedmelts.Theintermediatestagemeltformedtheremaininggarnetalongwithsomepyroxene,calcite,nepheline,andapatiteat127±3.6Ma.Theyoungest,mostevolvedmeltgeneratedthemajorityofpyroxene,calcite,nepheline,andapatitewithinthecalciticijoliteat115±3.1Ma.
简介:CATASTROPHEOFLITHOSPHERE┐ASTHENOSPHERESYSTEMANDYANSHANIANMETALLOGENICEXPLO┐SIONINEASTCHINATheoreticalConsiderationAnormallith...